redistribution of dynamic stress during coseismic ruptures evidence for fault interaction and earthquake triggering we investigate the spatiotemporal evolution of dynamic stress outside a rupturing extended fault the dynamic stress variations caused by a coseismic rupture in a half space are computed by using the discrete wavenumber and reflectivity methods after a transient phase the stress time history evolves to the final static stress value we compare the static stress changes resulting from this model with those computed from a static dislocation model we have applied this method to study the interactions between the first two normal faults which ruptured during the 1980 ms 6 9 irpinia earthquake these two subevents are separated in time by nearly 20 s while the third and last subevent occurred 40 s after the rupture onset we compute the dynamic stress changes caused by the rupture of the first subevent our modeling results show that the dynamic stress peak on the second subevent fault plane is reached between 7 s and 8 s after the rupture initiation on the main fault on the average the static stress level on the second subevent 20 s fault plane is reached nearly after 14 s the dynamic rupture did not jump from a rupturing segment to the adjacent one immediately but the triggering of the 20 s subevent is delayed by roughly 10 s with respect to the instant of occurrence of the dynamic stress peak induced by the 0 s event the dynamic stress pulse propagates along the strike direction of the second subevent fault plane at an average velocity of nearly 3 4 km s the delayed triggering of the second subevent can be interpreted in terms of the frictional properties of the faults in particular rate and state dependent frictional law can explain a delayed instability after a sudden change in stress using the estimated values of the subevent triggering delay and the shear stress change we attempt to constrain the parameter a on the 20 s fault the values here inferred agree well with those resulting from previous studies

stress triggering of large earthquakes complicated by transient aseismic slip episodes 1 we investigate how a static stress change caused by a nearby earthquake perturbs sliding processes on a fault and the time to the next earthquake for this purpose we model numerically a reverse fault in a two dimensional semi infinite and elastic medium partly stable and partly unstable under a rate and state dependent friction law when no stress change intervenes steady sliding spreads out of the deep zone of frictional stability and keeps expanding updip during the interseismic period aseismic slip episodes ases develop spontaneously within the region of steady sliding and repeat quasi periodically when steady sliding has spread beyond a certain critical length the nucleation length above the zone of frictional stability one of the ases undergoes rapid buildup and avalanches into high speed seismic sliding when a step like stress change intervenes ases of larger amplitudes arise and evolve similarly to their spontaneous counterparts until one of them avalanches into an earthquake if the stress change arrives not too early nor too late in the seismic cycle the basic picture is as follows delaying the stress step be it positive or negative delays the timing of the ase sequence and thereby postpones the next earthquake when the stress step is delayed to more than a certain extent however an earlier ase gets to evolve into an earthquake advancing its time discontinuously only in the final stage of a seismic cycle does a positive stress step systematically advance the next earthquake and a negative stress step systematically delay it

space time evolution of crustal deformation related to the mw 6 3 2009 l aquila earthquake central italy from principal component analysis inversion of gps position time series

crystallographic and structural transformations of sedimentary chalcedony in flint upon heat treatment the early occurrence of intentional heat treatment of silica rocks has recently become a key element in the discussion about the cultural modernity of prehistoric populations lithic vestiges are the only sources that remain of this process and the understanding of the material s properties and transformations are essential for reconstructing the conditions and parameters applied during heat treatment several models of the structural transformations upon heating have been proposed in the current literature these models are often contradictory and do not account for the most recent structural and mineralogical data on chalcedony in order to propose a new model we elaborated an experimental procedure and applied different techniques involving infrared spectroscopy solid state nmr x ray diffraction and electron microscopy the results show that the major transformation to happen is the loss of silanole sioh and the creation of new si o si bonds according to the reaction si oh ho si si o si h2o this reaction starts between 200 degrees c and 300 degrees c and causes an increase in the hardness of the rocks the maximal annealing temperature and the ramp rate are the functions of the ability of the structure to evacuate newly created h2o and depend on the size of the specimen and the volume of its porosity these results also show that the annealing duration at maximum temperature can be relatively short 50 min for a sufficiently large amount of transformation to be accomplished

middle oxfordian lower kimmeridgian chert nodules in the holy cross mountains south central poland abstract this report presents the results of field and laboratory micropaleontologic petrographic mineralogical chemical and isotopic study of middle oxfordian lower kimmeridgian chert nodules from the holy cross mountains south central poland the chert host facies represent low energy environments characteristic of changing basinal depths with subordinate influxes of coated carbonate grains derived from a prograding platform the optical microscopic and sem studies indicate that the chert nodules consist of cryptocrystalline quartz with subordinate microcrystalline quartz fills and lf chalcedony sponge spicules no opal a and opal ct precursors of the crypto and microquartz have been found these cherts formed as a result of an episodic influx of sio 2 rich fluids and multistage processes of direct precipitation of cryptoquartz dissolution etching reprecipitation cementation and recrystallisation of sponge spicules composed of metastable amorphous opal a of the different genetic models of chert formation the sea floor hydrothermal activity linked to the mid polish rift and extentional tectonics in the carpathian area seems to be a possible hypothesis

a new mechanism of slip weakening and strength recovery of friction associated with the mechanical consolidation of gouge i present results of a series of slide hold slide tests on granite surfaces separated by a layer of simulated granite gouge the shear stress during the hold period hold was controlled and used as a major control parameter of the experiments in addition to the time of hold time dependent fault healing which has been observed in many previous similar experiments was observed only at very high hold above 90 of the sliding friction a time independent strengthening termed consolidation strengthening occurred at all hold with a magnitude proportional to the reduction of hold the magnitude of this strengthening was as large as 25 of the residual friction the consolidation strengthening was found to be erased by subsequent slip in quite a different manner than is time dependent healing the friction decreased linearly with slip displacement at a rate independent of the magnitude of the strengthening and hence larger slip displacement is required to erase larger consolidation strengthening on the basis of these results together with earlier authors results of the measurements of porosity change under similar conditions i conclude that the time independent strengthening is due to the occurrence of gouge particle rearrangement to tighter packing enabled by decreased shear stress under a constant normal stress and that the subsequent slip weakening is due to unconsolidation of gouge enabled by particle rearrangement dilatancy during shearing the rate and state dependent friction rsf law was extended to incorporate the present findings

post seismic and interseismic fault creep i model description we present a model of localized aseismic fault creep during the full interseismic period including both transient and steady fault creep in response to a sequence of imposed coseismic slip events and tectonic loading we consider the behaviour of models with linear viscous non linear viscous rate dependent friction and rate and state dependent friction fault rheologies both the transient post seismic creep and the pattern of steady interseismic creep rates surrounding asperities depend on recent coseismic slip and fault rheologies in these models post seismic fault creep is manifest as pulses of elevated creep rates that propagate from the coseismic slip these pulses feature sharper fronts and are longer lived in models with rate state friction compared to other models with small characteristic slip distances in rate state friction models interseismic creep is similar to that in models with rate dependent friction faults except for the earliest periods of post seismic creep our model can be used to constrain fault rheologies from geodetic observations in cases where the coseismic slip history is relatively well known when only considering surface deformation over a short period of time there are strong trade offs between fault rheology and the details of the imposed coseismic slip geodetic observations over longer times following an earthquake will reduce these trade offs while simultaneous modelling of interseismic and post seismic observations provide the strongest constraints on fault rheologies

the geology of darwin crater western tasmania australia abstract darwin glass is a siliceous impact glass found in a 400 km 2 strewn field near mt darwin western tasmania australia it has been dated by ar ar methods at 816 7 ka a 1 2 km diameter circular depression named darwin crater 42 18 39 s 145 39 41 e is the assumed source crater for the glass darwin crater is situated in a remote rain forested valley developed within siluro devonian quartzite and slate eldon group earlier geophysical investigations demonstrated that the structure is an almost circular bowl shaped sediment filled basin this paper provides the first detailed description of the geology of darwin crater the centre of the crater has been penetrated by two drill cores the deeper to a maximum depth of 230 m the drill cores intersected fine grained lacustrine sediments 60 m thick overlying poorly sorted coarser crater fill deposits the pre lacustrine crater fill stratigraphy comprises an uppermost polymict breccia 40 m thick of angular quartz and country rock which contains very rare 1 fresh glass fragments crater fill facies a beneath the polymict breccia facies the drill core intersected monomict sandy breccias of angular quartz crater fill facies b and a complicated package of deformed slate clasts crater fill facies c quartz grains in the crater fill samples contain abundant irregular fractures in some of the most deformed quartz grains sub planar fractures define zones of alternating extinction that superficially resemble twinning kinked micas are also present while the deformation observed in clasts of the crater fill facies is far greater than in rocks cropping out around the crater no diagnostic shock indicators such as planar deformation features pdf s in quartz were observed if the crater is of impact origin as seems likely due to the close association with darwin glass this is another example of a simple crater where diagnostic shock indicators appear to be absent preventing confirmation of an impact origin by petrographic analysis of crater fill samples alone

silica diagenesis ii general mechanisms abstract amorphous silica phases opal a precipitate in nature due to the formation of dense colloids in supersaturated alkaline aqueous solutions with low relative concentrations of other ions opal a dissolves and yields solutions of still relatively high silica content in pore waters containing abundant cations open framework polymers form which flocculate to yield opal ct opal ct becomes increasingly ordered primarily due to preferential growth of cristobalite relative to tridymite and crystal size increase opal ct dissolves to yield pore waters of low silica concentration which allows slow growth of quartz crystals from monomeric solution the quartz crystals then slowly increase in size and crystallinity carbonates appear to enhance opal ct formation possibly due to the activity of positively charged hydroxyl complexes hence polymerization in relatively pure systems is involved in opal a formation and polymerization in impure systems is involved in opal ct formation and slow growth from monomeric low silica concentration solutions is involved in precipitation of quartz in sedimentary realms

strain softening of faults and earthquake precursors abstract a model for a strike slip fault is proposed in which an instability earthquake and or stable fault slip is produced by strain softening of the fault zone the form of the fault zone constitutive law and the stiffness and dimension of the surrounding elastic plates determine the fault slip and plate strain as a function of time and the potential for instability an instability is predictable from a developing plot of fault slip or plate strain if a single parameter the maximum strain softening slope of the fault zone constitutive law is known the amount of precursory fault creep and plate strain and hence the reliability and resolution of the prediction depends on the form of the constitutive law if the rate of strain softening is rapid precursors are virtually absent for very slow rates of strain softening precursors are large but temporal resolution of the expected instability may be poor the friction law on a fault segment may be inferred from observations of fault slip or surface strain as a function of time

stress diffusion along rupturing plate boundaries an analysis is made of viscoelastic lithosphere asthenosphere coupling in the time dependent redistribution of stress along plate boundaries or other seismic lineaments following great earthquakes the study is based on a generalization by rice of elsasser s model of stress diffusion in which general elastic plane stress deformations are allowed in lithospheric plates which are coupled in an elementary way to a maxwellian viscoelastic asthenosphere solutions are developed which describe the large scale quasistatic distribution of thickness averaged in the lithosphere at or near stationary or travelling rupture zones modeled here by either crack like zones of fixed stress drop or dislocation type slip zones sudden ruptures shed load onto the asthenosphere which is gradually transferred back to the lithosphere by a slow relaxation process the spatial and temporal characteristics of the predicted stress alterations suggest a significant role of lithosphere asthenosphere coupling effects in triggering interactions of great earthquakes patterns of prolonged aftershock activity and the breaking of barriers or gaps by time dependent stressing

effects of shear stress applied to surfaces in stationary contact on rock friction in this paper we show how the applied shear stress affects the frictional strength of granite sliding surfaces initially held in stationary contact we develop an experimental scheme to perform a slide and hold friction test whereby the shear stress is servocontrolled during the hold period of the test a series of experiments conducted at a single normal stress of 5 mpa show the following effects first unloading the shear stress during the hold period increases frictional resistance by up to 10 20 a decrease in shear stress linearly increases the frictional resistance of the interface secondly the static friction coefficient increases with the logarithm of contact time the friction coefficient increases by 0 01 per decade of contact time at near zero shear stress levels and by more than 0 02 at shear stress levels that are greater than half the sliding friction

magnetic properties of tektites and other related impact glasses we present a comprehensive overview of the magnetic properties of the four known tektite fields and related fully melted impact glasses aouelloul belize darwin libyan desert and wabar glasses irghizites and atacamaites namely magnetic susceptibility and hysteresis properties as well as properties dependent on magnetic grain size tektites appear to be characterized by pure fe2 paramagnetism with ferromagnetic traces below 1 ppm the different tektite fields yield mostly non overlapping narrow susceptibility ranges belize and darwin glasses share similar characteristics on the other hand the other studied glasses have wider susceptibility ranges with median close to paramagnetism fe2 and fe3 but with a high susceptibility population bearing variable amounts of magnetite this signs a fundamental difference between tektites plus belize and darwin glasses and other studied glasses in terms of oxygen fugacity and heterogeneity during formation thus bringing new light to the formation processes of these materials it also appears that selecting the most magnetic glass samples allows to find impactor rich material opening new perspectives to identify the type of impactor responsible for the glass generation

constitutive relations between dynamic physical parameters near a tip of the propagating slip zone during stick slip shear failure abstract constitutive relations between physical parameters in the cohesive zone during stick slip shear failure are experimentally investigated stick slip was generated along a 40 cm long precut fault in tsukuba granite samples using a servocontrolled biaxial loading apparatus dynamic behavior during local breakdown processes near a tip of the slipping zone is revealed the slip velocity and acceleration are given as a function of the slip displacement and the cohesive or breakdown shear stress as a function of the slip velocity a cycle of the breakdown and restrengthening process of stick slip is composed of five phases characterized in terms of the cohesive strength and the slip velocity the cohesive strength can degrade regardless of the slip velocity during slip instabilities the maximum slip acceleration u max and the maximum slip velocity u max are obtained experimentally as u max 2 u c u max 2 and u max b g v where u c is the critical displacement b the breakdown stress drop g the rigidity and v the rupture velocity these relations are consistent with ida s theoretical estimation based on the cohesive zone model the above formula gives good estimates for the maximum slip acceleration of actual earthquakes the cutoff frequency max of the power spectral density of the slip acceleration increases with increasing normal stress in particular max is found to be directly proportional to the normal stress n within the normal stress range less than 17 mpa as max khz 4 0 n mpa n max increase with an increase in u max or u max all these results lead to the conclusion that u max u max and max increase with increasing normal stress this is consistent with a previous observation that b increases with increasing normal stress the above empirical linear relation between max and n can be explained by a linear dependence of b on n the size scale dependence of physical parameters is discussed and such size scale dependent parameters as u max and apparent fracture energy are scaled to the breakdown zone size regarded as a characteristic length to extend the results obtained in the laboratory to an earthquake failure in the earth

lithic economy and territory of epipaleolithic hunter gatherers in the middle tagus the case of pena d agua portugal abstract in central portugal westernmost eurasia the transition from the traditional pleistocene hunter gatherer societies to the complex mesolithic societies of the holocene has been debated for decades while some argue that these differences were a progressive phenomenon that started with the shift from the pleistocene to the holocene others defend that the late pleistocene patterns were fairly similar to those of the epipaleolithic and that the major shift was rapid dramatic and triggered by the necessary adaptation to the 8 2 ka cal bp 8 09 8 25 ka cal bp climatic event the study of lithic raw material provenance might be useful for this discussion since it has been suggested that the magdalenian and epipaleolithic populations from this region were collecting this resources within a close range territory whereas the mesolithic populations were acquiring them at longer distances in this paper we present the results from p xrf vp sem eds and xrd analysis done on the epipaleolithic lithic assemblage from pena d agua rockshelter and in some geological samples from secondary sources located 14 km from this site this layer is of major relevance for this debate since it is dated from 8 19 ka cal bp if the transition was gradual it would be expected that this assemblage would show some traits of higher complexity seen in the mesolithic namely of longer distance acquisition however our results indicate correspondence between the archaeological chert types and some of the geological sources the differences seen between the archaeological specimens and geological samples are mostly present in traits that can be related with manufacture handling and post depositional phenomena the results suggest that in what concerns to the economy of abiotic resources the epipaleolithic populations living at the time of the dramatic 8 2 ka cal bp cold event were performing a short range acquisition of lithic raw materials which reinforces the idea of continuity from the late pleistocene to the 8 2 ka cal bp event and an abrupt and dramatic shift soon after this phenomena

effect of heat treatment on siliceous rocks used in prehistoric lithic technology stone tool manufacture by many prehistoric and recent societies was characterized by deliberate heating of fine grained siliceous rocks to improve their flaking properties extensive mechanical testing of heated and unheated cryptocrystalline and macrocrystalline quartz lithologies has shown that thermal treatment causes a consistent marked reduction in fracture toughness this mechanical property can be used as an objective measurement of the flaking qualities of stone materials and a reliable criterion for the recognition of intentionally heated artefacts in the archaeological record x ray diffraction studies and scanning electron microscopy have demonstrated that the change in fracture toughness with heating is the result of recrystallization the poorly ordered strongly interlocking cryptocrystalline fabric of the unheated samples becomes more equigranular and better crystallized with thermal treatment as a consequence fractures propagate more readily in heated samples accounting for their better flaking properties

fault friction parameters inferred from the early stages of afterslip following the 2003 tokachi oki earthquake 1 we use subdaily gps time series of positions in the first 5 hours following the 2003 tokachi oki earthquake mw 8 0 located offshore of hokkaido japan to estimate frictional parameters for the afterslip zone on the subduction interface the data show little motion immediately after the earthquake with sudden acceleration at about 1 2 hours after the main shock this coincides with the largest aftershock m 7 4 followed by gradual deceleration we assume that early afterslip is the response of a fault patch to instantaneous stress perturbations caused by the main shock and the largest aftershock early afterslip is modeled with a spring slider system obeying a rate and state dependent friction law we develop and apply an inversion method to estimate friction parameters dc a and a b where is effective normal stress the estimated 95 confidence intervals of dc a and a b are 2 6 10 4 to 1 8 10 3 m 0 29 to 0 43 mpa and 0 214 to 0 220 mpa respectively estimated dc is 10 to 103 times larger than typical laboratory values estimated a and a b values suggest that a and a b are smaller than typical laboratory values and or the pore pressure on the plate boundary is significantly elevated above the hydrostatic value our analyses show that the model can reproduce the observed gps data and that the timing of the rapid acceleration of postseismic deformation is controlled by the frictional properties of the fault and stress change from the main shock not by the timing of the largest aftershock

effects of load point velocity on frictional instability behavior abstract triaxial experiments were conducted on sawcut westerly granite specimens sandwiched with a simulated gouge layer of ultrafine quartz over a wide range of normal stresses from 25 to 250 mpa tens and sometimes hundreds of repeated stick slip events were observed to persist over a total slip displacement up to 10 mm a transition from stick slip to stable sliding was observed as the result of cumulative slip displacement the total slip displacement over which repeated stick slip instabilities occurred before the transition to stable sliding decreases with increasing normal stress the stress drop amplitude decreases with increasing load point velocity the experimentally determined stress drop amplitude was also found to increase as a function of the time of stationary contact the dependence of stress drop amplitude on load point velocity and on time of stationary contact can be characterized empirically by a power law preliminary data suggest that the two effects are coupled the seismological implications of the experimental data are discussed at relatively high normal stresses above 250 mpa no systematic dependence of stress drop amplitude on load point velocity was observed an increase in gouge particle size stabilizes the frictional instability behavior a mixed mode of velocity weakening and velocity strengthening behavior was occasionally observed

frictional constraints on crustal faulting we consider how variations in fault frictional properties affect the phenomenology of earthquake faulting in particular we propose that lateral variations in fault friction produce the marked heterogeneity of slip observed in large earthquakes we model these variations using a rate and state dependent friction law where we differentiate velocity weakening behavior into two fields the strong seismic field is very velocity weakening and the weak seismic field is slightly velocity weakening similarly we differentiate velocity strengthening behavior into two fields the compliant field is slightly velocity strengthening and the viscous field is very velocity strengthening the strong seismic field comprises the seismic slip concentrations or asperities the two intermediate fields weak seismic and compliant have frictional velocity dependences that are close to velocity neutral these fields modulate both the tectonic loading and the dynamic rupture process during the interseismic period the weak seismic and compliant regions slip aseismically while the strong seismic regions remain locked evolving into stress concentrations that fail only in main shocks the weak seismic areas exhibit most of the interseismic activity and aftershocks but can also creep seismically this mixed frictional behavior can be obtained from a sufficiently heterogeneous distribution of the critical slip distance the model also provides a mechanism for rupture arrest dynamic rupture fronts decelerate as they penetrate into unloaded complaint or weak seismic areas producing broad areas of accelerated afterslip aftershocks occur on both the weak seismic and compliant areas around a fault but most of the stress is diffused through aseismic slip rapid afterslip on these peripheral areas can also produce aftershocks within the main shock rupture area by reloading weak fault areas that slipped in the main shock and then healed we test this frictional model by comparing the seismicity and the coseismic slip for the 1966 parkfield 1979 coyote lake and 1984 morgan hill earthquakes the interevent seismicity and aftershocks appear to occur on fault areas outside the regions of significant slip these regions are interpreted as either weak seismic or compliant depending on whether or not they manifest interevent seismicity

the earthquake deformation cycle at the nankai trough southwest japan geodetic measurements made landward of the nankai trough site of great subduction zone thrust earthquakes in 1854 and 1946 provide a uniquely detailed picture of the strain buildup process supply constraints on the mechanism of strain accumulation and allow for improved estimates of earthquake recurrence provided the two most recent movement cycles are similar the observations dating from about 1890 may be used to reconstruct a single complete deformation cycle coseismic strain release postseismic transients interseismic strain accumulation very complete leveling and tidal gage data indicate that postseismic deformation extends more than 300 km inland from the plate boundary persists for at least 30 years and shows a clear tendency to become longer wavelength with increasing time the transient movements have two timescales the first of about a year or less corresponds to deformation largely uplift concentrated close to the coseismic fault and is most easily explained by aseismic slip or very localized deformation downdip of the earthquake rupture plane the second longer timescale is associated with a diffusion like spread of the deformation further landward an effect qualitatively similar to that first predicted by elsasser to be an expected consequence of faulting in an elastic plate overlying a viscoelastic asthenosphere cumulative uplift since 1890 correlates well with the distribution of uplifted marine terraces although average post 1890 tilt rates exceed late quaternary and holocene averages by at least a factor of three because of the nonlinearity of strain buildup and the significant permanent deformation simple recurrence calculations typically overestimate the true interval between great earthquakes by a factor of 2 to a factor of 3 strict application of the time predictable model assumed correct overcomes these difficulties provided the cumulative transient deformation and the proportion of permanent deformation per cycle can be estimated

slip dependent friction law and nucleation processes in earthquake rupture abstract matsu ura m kataoka h and shibazaki b 1992 slip dependent friction law and nucleation processes in earthquake rupture in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 135 148 we developed a physical model that interprets slip strengthening and slip weakening processes in brittle shear fracture by considering the microscopic interaction between statistically self similar fault surfaces our model successfully describes general features of the constitutive behaviour observed in laboratory experiments of stick slip with the progress of fault slip frictional stress first increases rapidly up to a peak value and then decreases gradually to a constant level the first slip strengthening process can be explained by the increase of frictional resistance in transition from the in phase contact to the random phase contact of fault surfaces the latter slip weakening process can be explained by the decrease of frictional resistance due to the abrasion of surface asperities the trade off between these two processes determines the peak stress and the critical displacement over which the slip weakening proceeds we examined the nucleation process proceeding in a seismogenic zone with the increase of external shear stress through numerical simulations in our model the seismogenic zone is represented by a broad weak zone with a locally strong part asperity on a fault plane the basic equations governing the nucleation process are the equation of equilibrium and the constitutive relation between frictional stress and fault slip we obtained the following results the nucleation process first proceeds quasi statically at the weak portions with the increase of external shear stress then if the constitutive relation at the asperity has a high and narrow peak of stress brittle dynamic rupture occurs in a limited area around the asperity when the constitutive relation has a low and broad peak the dynamic rupture of the asperity does not occur the process is completely aseismic when the peak of stress is high and broad the dynamic rupture of the asperity leads to the catastrophic rupture which extends over the whole region from these results it is concluded that diversity in the nucleation process can be ascribed to difference in the variation of constitutive behaviour along the fault

on the mechanics of earthquake afterslip we propose a model for earthquake afterslip based on rate and state variable friction laws in the model afterslip is attributed to the interaction of a velocity weakening region at depth within which earthquakes nucleate with an upper region of velocity strengthening frictional behavior the existence of this upper region is supported by independent seismologic observations and the results of laboratory friction experiments in our model afterslip is the result of relaxation of a stress perturbation within the velocity strengthening region which arises when an earthquake propagates into that region from below we derive the stress perturbation and its decay from the friction constitutive law using a simple 1 degree of freedom approximation for the elastic interaction between the fault and its surroundings this approximation is based on thickness averaged displacements and slip velocities within the velocity strengthening region which is assumed to slip as a rigid block coseismic and postseismic slip are coupled through the thickness averaged stiffness k of the velocity strengthening region we assume k to be inversely proportional to the thickness of this region which means that thicker velocity strengthening regions have a greater tendency to arrest coseismic slip we model the afterslip time histories of the 1966 parkfield and 1987 superstition hills earthquakes and relate the model parameters to physical parameters which may govern the rheologic behavior of the faults in accord with field observations our model predicts 1 that afterslip on some faults scales with the thickness of the unconsolidated sedimentary cover and 2 that proportionally more afterslip occurs for earthquakes in which coseismic surface slip is small compared with coseismic slip at depth velocity strengthening frictional behavior is to be expected for faults within poorly consolidated sediments and for those that contain significant gouge zones about 500 m within their shallow regions 3 5 km combining our results with those of recent laboratory friction studies indicates that relatively young faults with little accumulated fault gouge should exhibit little afterslip

imaging of aseismic fault slip transients recorded by dense geodetic networks summary the large scale continuous gps networks that have emerged in the last decade have documented a wide range of aseismic deformation transients that resulted from physical processes such as aseismic fault slip and magma intrusion in particular a new class of m 7 slow earthquakes with durations ranging from days to months have been observed with gps arrays located above the downdip portion of subduction zone thrust interfaces interpretation of the displacement time series resulting from these events is not straightforward owing to the contaminating effects of multiple contributing signals such as fault slip local benchmark motion seasonal effects and reference frame errors we have developed a time dependent inversion algorithm based on the extended kalman filter which can separate the various signals and allow the space time evolution of these slow slip transients to be studied in detail we applied the inversion algorithm to the 1999 cascadia slow earthquake this event had two primary episodes of moment release separated by a two week period in which relatively little moment release occurred the cascadia event and other slow earthquakes share numerous similarities with both ordinary earthquakes and afterslip transients suggesting that they may represent fault slip under a conditionally stable regime

strontium and neodymium isotopic study of libyan desert glass inherited pan african age signatures and new evidence for target material libyan desert glass ldg is an impact related natural glass of still unknown target material we have determined rb sr and sm nd isotopic ratios from seven ldg samples and five associated sandstones from the ldg strewn field in the great sand sea western egypt planar deformation features were recently detected in quartz from these sandstones 87sr 86sr ratios and e nd values for ldg range between 0 71219 and 0 71344 and between 16 6 and 17 8 respectively and hence are distinct from the less radiogenic 87sr 86sr ratios of 0 70910 0 71053 and e nd values from 6 9 to 9 6 for the local sandstones from the ldg strewn field previously published isotopic ratios from the libyan bp and oasis crater sandstones are generally incompatible with our ldg values ldg formation undoubtedly occurred at 29 ma but neither the rb sr nor the sm nd isotopic system were rehomogenised during the impact event as we can deduce from pan african ages of 540 ma determined from the regression lines from a total of 14 ldg samples from this work and the literature together with similar sr and nd isotopic values for ldg and granitoid rocks from northeast africa west of the nile these findings point to a sandy matrix target material for the ldg derived from a precambrian crystalline basement ruling out the cretaceous sandstones of the former nubian group as possible precursors for ldg

nucleation and triggering of earthquake slip effect of periodic stresses abstract results of stability analyses for spring and slider systems with state variable constitutive properties are applied to slip on embedded fault patches unstable slip may nucleate only if the slipping patch exceeds some minimum size subsequent to the onset of instability the earthquake slip may propagate well beyond the patch it is proposed that the seismicity of a volume of the earth s crust is determined by the distribution of initial conditions on the population of fault patches that nucleate earthquake slip and the loading history acting upon the volume patches with constitutive properties inferred from laboratory experiments are characterized by an interval of self driven accelerating slip prior to instability if initial stress exceeds a minimum threshold this delayed instability of the patches provides an explanation for the occurrence of aftershocks and foreshocks including decay of earthquake rates by time 1 a population of patches subjected to loading with a periodic component results in periodic variation of the rate of occurrence of instabilities the change of the rate of seismicity for a sinusoidal load is proportional to the amplitude of the periodic stress component and inversely proportional to both the normal stress acting on the fault patches and the constitutive parameter a 1 that controls the direct velocity dependence of fault slip values of a 1 representative of laboratory experiments indicate that in a homogeneous crust correlation of earthquake rates with earth tides should not be detectable at normal stresses in excess of about 8 mpa correlation of earthquakes with tides at higher normal stresses can be explained if there exist inhomogeneities that locally amplify the magnitude of the tidal stresses such amplification might occur near magma chambers or other soft inclusions in the crust and possibly near the ends of creeping fault segments if the creep or afterslip rates vary in response to tides observations of seismicity rate variations associated with seasonal fluctuations of reservoir levels appear to be consistent with the model

fault interaction near hollister california a numerical model is used to study fault stress slip near hollister california the geometrically complex system of interacting faults including the san andreas calaveras sargent and busch faults is approximated with a two dimensional distribution of short planar fault segments in an elastic medium the steady stress and slip rate are simulated by specifying frictional strength and stepping the remote stress ahead in time the resulting computed fault stress is roughly proportional to the observed spatial density of small earthquakes suggesting that the distinction between segments characterized by earthquakes and those with aseismic creep results in part from geometry a nonsteady simulation is made by introducing in addition stress drops for individual moderate earthquakes a close fit of observed creep with calculated slip on the calaveras and san andreas faults suggests that many changes in creep rate averaged over several months are caused by local moderate earthquakes in particular a 3 year creep lag preceding the august 6 1979 coyote lake earthquake on the calaveras fault seems to have been a direct result of the november 28 1974 thanksgiving day earthquake on the busch fault computed lags in slip rate preceding some other moderate earthquakes in the area are also duemore to earlier earthquakes although the response of the upper 1 km of the fault zone may cause some individual creep events and introduce delays in others the long term rate appears to reflect deep slip less

age and provenance of the target materials for tektites and possible impactites as inferred from sm nd and rb sr systematics sm nd and rb sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of target materials which were impact melted to form these objects tektites have large negative e nd 0 values and are uniform within each tektite group while the e sr 0 are large positive values and show considerable variation within each group chemical trace element and isotopic compositions of tektites are consistent with production by melting of sediments derived from old terrestrial continental crust each tektite group is characterized by a uniform nd model age t chur nd interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites 1 1 15 ae for australasian tektites 2 1 91 ae for ivory coast tektites 3 0 9 ae for moldavites 4 0 65 ae for north american tektites and 5 0 9 ae for high si irghizites sr model ages t ur sr are variable within each group reflecting rb sr fractionation and in the favorable limit of very high rb sr ratios approach the time of sedimentation of the parent material which melted to form the tektites australasian tektites are derived from 0 25 ae sediments moldavites from 0 0 ae sediments ivory coast tektites from 0 95 ae sediments possible parent sediments of other tektite groups have poorly constrained ages our data on moldavites and ivory coast tektites are consistent with derivation from the ries and bosumtwi craters respectively irghizites are isotopically distinct from australasian tektites and are probably not related sanidine spherules from a cretaceous tertiary boundary clay have initial e nd 2 e sr 5 and are not derived from old continental crust or meteoritic feldspar they may represent a mixture of basaltic oceanic crust and sediments implying an oceanic impact these isotopic results are also consistent with a volcanic origin for the spherules

geochemistry of darwin glass and target rocks from darwin crater tasmania australia darwin glass formed about 800 000 years ago in western tasmania australia target rocks at darwin crater are quartzites and slates siluro devonian eldon group analyses show 2 groups of glass average group 1 is composed of sio2 85 al2o3 7 3 tio2 0 05 feo 2 2 mgo 0 9 and k2o 1 8 group 2 has lower average sio2 81 1 and higher average al2o3 8 2 group 2 is enriched in feo 1 5 mgo 1 3 and ni co and cr average ni 416 ppm co 31 ppm and cr 162 ppm in group 2 are beyond the range of sedimentary rocks glass and target rocks have concordant ree patterns la lu 5 910 eu eu 0 55 0 65 and overlapping trace element abundances 87sr 86sr ratios for the glasses 0 80778 0 81605 fall in the range 0 76481 1 1212 defined by the rock samples e nd results range from 13 57 to 15 86 nd model ages range from 1 2 1 9 ga chur and the glasses 1 2 1 5 ga fall within the range defined by the target samples the 87sr 86sr versus 87rb 86sr regression age 411 42 ma and initial ratio 0 725 0 016 and the initial 43nd 144nd ratio 0 51153 0 00011 and regression age 451 140 ma indicate that the glasses have an inherited isotopic signal from the target rocks at darwin crater mixing models using target rock compositions successfully model the glass for all elements except feo mgo ni co and cr in group 2 mixing models using terrestrial ultramafic rocks fail to match the glass compositions and these enrichments may be related to the projectile

models of aftershock occurrence summary the omori formula for aftershock activity can be shown to be a consequence of each of two models of a complex earthquake in the first case aftershocks are assumed to be caused by subsequent slip on asperities of a fault which are locked during the fracture in the main shock in the second aftershocks are caused by catastrophic coalescence of nearby small fractures with the fracture surface of the main shock hence the first source model describes aftershock activity in the interior of a main shock rupture zone while the second describes aftershock activity near the outer boundary of a main shock rupture zone stress corrosion cracking is assumed to be the physical cause of the quasistatic growth of the main fracture zone at the expense of the area of the locked patches in the first model and is also the cause of the growth of the small satellite fractures in the second

constitutive behavior and stability of frictional sliding of granite an understanding of the frictional sliding on faults that can lead to earthquakes requires a knowledge of both constitutive behavior of the sliding surfaces and its mechanical interaction with the loading system we have determined the constitutive parameters for frictional sliding of initially bare surfaces of westerly granite using a recently developed high pressure rotary shear apparatus that allows long distances of sliding and therefore a greater assurance of attaining steady state behavior from experiments conducted at room temperature and normal stresses of 27 84 mpa several important results have been found 1 a gouge layer 100 to 200 m thick was developed from the initially bare rock surfaces after 18 to 70 mm of sliding 2 the steady state frictional resistance attained after about 10 mm of sliding is proportional to the negative of the logarithm of the sliding velocity 3 abrup changes in the velocity of sliding result in initial changes in the frictional resistance which have the same sign as the velocity change and are followed by a gradual decay to a new steady state value over a characteristic distance of sliding this velocity weakening behavior is essentially identical with that found by several previous workers on the same material at lower normal stress 4 our results are well described by a two state variable constitutive law the values of the constitutive parameters are quite similar to those found previously at low normal stress but the characteristic distance is about an order of magnitude smaller than that found at 10 mpa normal stress with thicker layers of coarser gouge 5 we have approximated our results with a one state variable constitutive law and compared the results with the predictions of existing nonlinear stability analysis in addition we have extended the stability analysis to systems possessing two state variables with such formulations good agreement is found between the experimentally observed and theoretically predicted transitions between stable and unstable sliding these results allow a better understanding of the instabilities that lead to earthquakes

earthquake triggering by static and dynamic stress changes 1 in this study we aim to understand the effect of static and dynamic stress changes in promoting earthquake failures on secondary faults toward this goal we solve the equation of motion of a spring slider dynamic system including inertia and using rate and state dependent constitutive laws we separately investigate the dynamic response of this fault analog system to a sudden stress change represented either as a stress step or as a stress pulse which are used to model permanent static and transient dynamic stress perturbations the induced earthquake failure does not occur immediately at the application of the coseismic stress change but it is delayed in time we define this time interval as the triggering delay for a given stress perturbation we analyze the dependence of triggering delays on different system conditions and constitutive parameters our results clearly show that the effects of static and dynamic stress changes are quite different while a static stress change is able to advance as well as to delay an induced instability depending on its sign a dynamic stress pulse is only able to promote a nearly instantaneous failure provided its amplitude is positive and large enough with respect to the direct effect of friction in other words dynamic stress changes can only cause nearly instantaneous failures without any relevant triggering delay these results should be considered in interpreting the seismicity rate changes caused by large earthquakes at least as long as seismic events are interpreted as sliding instabilities obeying rate and state dependent friction laws

crustal earthquake instability in relation to the depth variation of frictional slip properties recent stability studies using constitutive relations of the type found by dieterich ruina and others to describe frictional slip of rocks in the laboratory have provided a new explanation of the depth cutoff of shallow crustal earthquakes the class of friction laws discussed has the property that the sliding stress depends on normal stress temperature slip rate and slip history for sliding at a fixed slip rate v and fixed environment e g normal stress temperature etc the shear strength evolves toward a steady state value ss v stability analysis show that for d ss v dv 0 velocity strengthening implies stable steady state sliding at least for a broad class of constitutive laws more fully described in the paper experiments by dieterich and by tullis and weeks on westerly granite with mature sliding surfaces indicate that d ss v dv is negative at room temperature whereas higher temperature experiments by stesky show that d ss v dv becomes positive above approximately 300 c therefore in the case of the earth where temperature increases with depth the above observations seem to suggest that the depth cutoff of crustal earthquake activity can be understood in terms of the variation of the frictional response with depth from a regime with d ss v dv 0 this is not inconsistent with but rather refines the suggestion by sibson and others that the depth cutoff is due to a transition from brittle friction to ductile flow further our results show definitively that the shallow depth confinement of seismicity is compatible with a model in which deformation is localized to a fault zone extending well below the seismogenic depth the depth confinement does not require a model showing transition to a zone of broadly distributed creep flow beneath the seismogenic zone following mavko a two dimensional quasi static strike slip fault model is analyzed but using different numerical procedures and a depth variation of frictional properties based on the laboratory data mentioned above and the lachenbruch sass depth variation of temperature for the san andreas fault the resulting predictions of such features as the confinement of crustal earthquakes to shallow depths the development of locked patches the recurrence time for the seismic cycle the seismic stress drop and displacement etc are generally in agreement with the observed characteristics of large scale strike slip earthquakes along the san andreas fault calculations based on the laboratory data predict for example that stick slip nucleates around 5 7 km that large seismic motion occurs around the nucleation depth and above but diminishes gradually to zero at 13 15 km depths that rapid postseismic creep occurs over another 3 4 km depth and that at greater depths steady slip consistent with the average plate velocity is only modestly perturbed by the earthquakes occurring above the most uncertain parameter is the slip weakening distance l for evolution of fault surface state we illustrate how features of the predicted earthquake cycles vary with l over the range for which calculations are feasible

the black layer of middle palaeolithic combustion structures interpretation and archaeostratigraphic implications certain aspects of the formation processes of simple flat archaeological combustion structures such as those present in the middle palaeolithic record remain unexplained such kind of combustion structures are commonly affected by postdepositional agents and often their only distinct well preserved component is a thin black lens on the ground hence understanding the nature of this black lens is essential towards archaeological interpretation from an interdisciplinary microstratigraphic approach we present a case study in which for an entire experimental series of flat combustion structures the black layer represents the fire altered topsoil on which the fire was made parallel analysis of archaeological middle palaeolithic combustion structures from the site of el salt alicante spain reveal similar patterns leading to significant implications for archaeological interpretation in the light of these results special attention must be paid to the formation processes of flat middle palaeolithic combustion features as black layers and the material contained in them are not necessarily linked with combustion but with preceding activities or events in such cases black layers represent intact remnants of occupation surfaces concealing significant behavioural and palaeoenvironmental information relevant to the reconstruction of middle palaeolithic societies

seismicity in a model governed by competing frictional weakening and healing mechanisms summary observations from laboratory field and numerical work spanning a wide range of space and time scales suggest a strain dependent progressive evolution of material properties that control the stability of earthquake faults the associated weakening mechanisms are counterbalanced by a variety of restrengthening mechanisms the efficiency of the healing processes depends on local material properties and on rheologic temperature and hydraulic conditions we investigate the relative effects of these competing non linear feedbacks on seismogenesis in the context of evolving frictional properties using a mechanical earthquake model that is governed by slip weakening friction weakening and strengthening mechanisms are parametrized by the evolution of the frictional control variable the slip weakening rate r using empirical relationships obtained from laboratory experiments in our model weakening depends on the slip of an earthquake and tends to increase r following the behaviour of real and simulated frictional interfaces healing causes r to decrease and depends on the time passed since the last slip results from models with these competing feedbacks are compared with simulations using non evolving friction compared to fixed r conditions evolving properties result in a significantly increased variability in the system dynamics we find that for a given set of weakening parameters the resulting seismicity patterns are sensitive to details of the restrengthening process such as the healing rate b and a lower cutoff time t c up to which no significant change in the friction parameter is observed for relatively large and small cutoff times the statistics are typical of fixed large and small r values respectively however a wide range of intermediate values leads to significant fluctuations in the internal energy levels the frequency size statistics of earthquake occurrence show corresponding non stationary characteristics on time scales over which negligible fluctuations are observed in the fixed r case the progressive evolution implies that except for extreme weakening and healing rates faults and fault networks possibly are not well characterized by steady states on typical catalogue time scales thus highlighting the essential role of memory and history dependence in seismogenesis the results suggest that an extrapolation to future seismicity occurrence based on temporally limited data may be misleading due to variability in seismicity patterns associated with competing mechanisms that affect fault stability

time dependent friction of granite implications for precursory slip on faults frictional forces were measured during sliding between saw cut cylinders of barre granite deformed in a servo controlled triaxial loading machine two different effects occur depending on the type of loading when steady shortening of a stably sliding sample is halted suddenly slip continues at a diminishing rate which depends on the logarithm of the initial sliding velocity thus the frictional strength of the surface is decreasing with time when shortening at a constant rate resumes after the holding period however the frictional resistance temporarily rises to a peak proportional to the logarithm of time of no driving showing a well known increase in friction with time the subsequent decrease in resistance from this peak is continuous the observed frictional resistance of a surface thus results from the interaction of several processes and is not a constant in general but depends on the immediate and preceding deformation when shortening is resumed after a period of holding slip rate across the friction surface temporarily accelerates above the driving rate the slip rate can then either decrease to the driving rate and remain stable or accelerate further and lead to stick slip motion at stress levels below the peak value there is no apparent difference in the frictional resistance until the unloading rate of the loading machine is exceeded between slip episodes which settle stably to the constant driving rate and those which become unstable and result in stick slip the stick slip failure criterion is not a peak stress but rather loss of strength more rapidly that the unloading rate of the loading machine the evidence that accelerating motion before stick slip is due to the time variable strength of rock suggests that accelerating slip will occur before earthquakes unfortunately for easy observation experiments indicate that slip need not be uniform over a fault surface also to be established is whether slip will be sufficiently large in the earth to be detectable nevertheless a plausible mechanism for generating observable phenomena prior to earthquakes is suggested by the laboratory observations

healing and sliding stability of simulated anhydrite fault gouge effects of water temperature and co2 abstract anhydrite bearing faults are currently of interest to 1 co2 storage sites capped by anhydrite caprocks such as those found in the north sea and 2 seismically active faults in evaporite formations such as the italian apennines in order to assess the likelihood of fault reactivation the mode of fault slip and or fault leakage it is important to understand the evolution of frictional strength during periods of no slip and upon reloading healing and relaxation behavior and of the velocity dependence of friction of anhydrite fault gouge therefore we performed slide hold slide experiments combined with a velocity stepping sequence using simulated anhydrite fault gouge 95 wt caso4 vacuum dry and water wet experiments were performed at temperatures ranging from 20 to 150 c and at an effective normal stress of 25 mpa we also performed tests using dry co2 water wetted co2 and co2 saturated water as pore fluid but only at 120 c if pore fluid was present a fluid pressure of 15 mpa was present vacuum dry samples exhibit similar frictional healing to samples containing lab air but healing is significantly enhanced in wet samples dry samples exhibit velocity weakening behavior at t 120 c and wet samples exhibit velocity strengthening behavior over the full temperature range the presence of co2 does not influence the healing behavior or the velocity dependence of friction samples containing water wetted co2 exhibit behavior similar to wet samples we infer that the healing in dry samples is controlled by plastic asperity creep dieterich type possibly through dislocation creep and or twinning in wet samples healing is inferred to be controlled by increases in contact area and cohesion by pressure solution using a pressure solution rate model to extrapolate healing by contact area growth indicates that the maximum re strengthening through such a mechanism will only take days to tens of days

probability of earthquake recurrence with nonuniform stress rates and time dependent failure current methods for calculation of long term probabilities for the recurrence of large earthquakes on specific fault segments are based upon models of the faulting process that implicitly assume constant stress rates during the interval separating earthquakes and instantaneous failure at a critical stress threshold however observations indicate that the process of stress recovery following an earthquake involves rate variations at all time scales in addition to stress steps caused by nearby earthquakes additionally the existence of foreshocks aftershocks and possible precursory processes suggest that there may be significant time dependence of the earthquake nucleation process a method for determining the conditional probabilities for earthquake occurrence under conditions of irregular stressing is developed that could be useful at all time scales including those pertinent to short and intermediate term prediction used with models for earthquake occurrence at a stress threshold the addition of variable stressing introduces a simple scaling of the conditional probabilities by stress level and stress rate a model for the time dependent nucleation of earthquake slip has been proposed recently that is based upon laboratory observations of fault strength this failure criterion results in large but relatively short duration changes in the probability of earthquake recurrence particularly following stress steps applied to populations of earthquakes the models predicts a 1 t decay of seismicity following stress steps as observed for aftershocks and for frequency of foreshock mainshock pairs the model suggests that variations of seismicity rates of small earthquakes in the nucleation zone of the expected earthquake directly indicate variations in probability of recurrence of the large earthquake

physical distribution trends in darwin glass darwin glass formed by impact melting probably during excavation of the 1 2 km diameter darwin crater tasmania australia the glass was ejected up to 20 km from the source crater and forms a strewn field of 400 km 2 there is at least 11 250 m 3 of glass in the strewn field and relative to the size of the crater this is the most abundant ejected impact glass on earth the glass population can be subdivided on the basis of shape 74 irregular 20 ropy 0 5 spheroid 6 droplet and 0 7 elongate and color 53 dark green 31 light green 11 black and 5 white the white glasses contain up to 92 wt sio2 and are formed from melting of quartzite black glasses contain a minimum of 76 wt sio2 and formed from melting of shale systematic variations in the proportion of glasses falling into each of the color and shape classes relative to distance from the crater show 1 a decrease in glass abundance away from the crater 2 the largest fragments of glass are found closest to the crater 3 small fragments 2 g dominate finds close to the crater 4 the proportion of white glass is greatest closest to the crater 5 the proportion of black glass increases with distance from the crater and 6 the proportion of splashform glasses increases with distance from the crater these distribution trends can only be explained by the molten glass having been ballistically ejected from darwin crater during impact and are related to 1 the depth of excavation from the target rock stratigraphy and or 2 viscosity contrasts between the high and low sio2 melt the high abundance and wide distribution of ejected melt is attributed to a volatile charged target stratigraphy produced by surface swamps that are indicated by the paleoclimate record

interactions between the landers and hector mine california earthquakes from space geodesy boundary element modeling and time dependent friction the m w 7 1 hector mine earthquake happened 7 years after the 1992 m w 7 3 landers earthquake within a system of right lateral strike slip faults comprising the eastern california shear zone because estimates of recurrence intervals of m 7 earthquakes on these faults range anywhere from 1500 to 50 000 years the close temporal spacing of these two earthquakes suggests that there is some interaction between the two current models of simple coulomb static stress interactions between the earthquake ruptures do not predict an obvious cause and effect relationship the interaction between the computed normal and right lateral shear stress reductions induced by the landers earthquake at the hector mine hypocenter is unclear we use a combination of space geodesy boundary element modeling and computer modeling of time dependent fault friction to investigate the interaction between the two earthquakes we compare stress changes on the hector mine rupture plane induced by the landers earthquake with the detailed slip distribution inferred using a combination of gps and insar data the slip distributions of both earthquakes are also used to infer the magnitude of the shear stress drop on each earthquake rupture and the orientation of the remote background stress consistent with these two recent events for each earthquake the azimuth of the remote maximum compressive stress was approximately 17 6 and the magnitude of the shear stress drop was 8 1 mpa on the landers rupture and 10 2 mpa on the hector mine rupture using a simple spring and slider model as a proxy for the rate and state frictional response of the hector mine faults to landers earthquake imposed stress steps we find that while a decrease in normal stress at the hector mine hypocenter would by itself have caused the hector mine earthquake to nucleate immediately the simultaneous decrease in shear stress may have caused a delay in the peak shear loading consideration of an acceptable range of rate and state friction parameters secular strain rates and crustal stiffnesses leads us to conclude that this delay could have been 0 to 40 years

first evidence of heat treatment during the early neolithic in northeastern italy the site of la vela sector vii trentino alto adige italy provides one of the few complete stratigraphic sequences ranging from the mesolithic to the middle neolithic in northwestern italy the site is located in the adige valley a way of communication between the po plan and the alps this research focuses on the early neolithic lithics ascribable to the gaban facies dated to 5000 4700 cal bc different rocks coming from local exposures have been exploited the goal of the reduction sequence was the production of blades by pressure knapping technique the technological study of the assemblage raised a particular interest for the presence of flint artifacts suggesting the usage of controlled heat treatment the presence of this technique has been tested by an experimental approach based on fourier transform infrared ft ir spectroscopy complementary microstructural and analytical characterizations with low vacuum scanning electron microscopy lvsem observations combined with energy dispersive x ray spectroscopy edxs have been performed the analyses confirm the presence of artifacts intentionally heat treated the thermal treatment achieved in order to increase the quality of the blade production is the first evidence of this technique in northeastern italy during the early neolithic

laser fusion argon 40 argon 39 ages of darwin impact glass three samples of darwin glass an impact glass found in tasmania australia at the edge of the australasian tektite strewn field were dated using the 40ar 39ar single grain laser fusion technique yielding isochron ages of 796 815 ka with an overall weighted mean of 816 7 ka these data are statistically indistinguishable from those recently reported for the australasian tektites from southeast asia and australia 761 816 ka with a mean weighted age of 803 3 ka however considering the compositional and textural differences and the disparity from the presumed impact crater area for australasian tektites darwin glass is more likely to have resulted from a distinct impact during the same period of time

effects of a revised rate and state dependent friction law on aftershock triggering model abstract seismicity may be considered as a sequence of earthquake nucleation events controlled by regional loading history on the basis of this concept dieterich 1994 modeled aftershock seismicity following an imposed stress step by using a laboratory derived rate and state dependent friction law rsf although this model predicts the canonical 1 t decay of aftershock rate two huge gaps from observations are known the model with frictional parameters assumed to be laboratory observed values predicts too low aftershock productivity and also too long a delay before the decay onset these gaps are by orders of magnitude we suspected that the problem might be the incorrectness of traditional rsfs none of which was free from contradictions with laboratory data hence we modeled aftershock triggering with a revised rsf nagata et al 2012 which seems to have resolved the previously known flaws in reproducing laboratory data the original analytic approach of dieterich 1994 was found invalid for the revised rsf so we did an equivalent analysis by numerically tracking individual nucleation sources the revised rsf produced generally similar aftershock seismicity with the gaps mentioned above narrowed by a factor though these are far too small improvements of the huge gaps that is the revised rsf did not fully resolve the problem on the other hand our simulations found a counterintuitive response of a fault obeying the revised rsf if imposed during a certain stage in the seismic cycle a positive stress step can cause oscillatory slow slip events before eventual seismic instability instead of a usual response of further monotonic acceleration to seismic instability this delays the timing of the next earthquake due to this behavior the exponent of the aftershock decay can be greater than unity also the decay can once overshoot below the background seismicity before eventually returning to the background level

rapid postseismic strength recovery of pingxi fault gouge from the longmenshan fault system experiments and implications for the mechanisms of high velocity weakening of faults 1 slide hold slide tests were conducted on gray blackish gouge gbg and yellowish gouge yg from pingxi fault zone to see how rapidly the strength of longmenshan fault recovers after the 2008 wenchuan earthquake twenty dry runs were made at a normal stress of 0 8 mpa at a seismic slip rate of 1 4 m s and with hold time th ranging 0 3 105 s results exhibit very rapid healing by more than 0 4 in friction coefficient in less than 5 10 s followed by gradual healing in proportion to log th healing rates increase in log th during rapid and slow healing are 0 188 and 0 015 for gbg and 0 154 and 0 016 for yg respectively the average temperature in the outer half of a 5 m thick slip zone decreases from 260 300 c to 110 170 c in 5 10 s and hence temperature drop appears to be correlated with the rapid healing previously reported rapid healing at subseismic slip rates 85 90 mm s begins to occur in 10 300 s after the stop of sliding and this cannot be explained by the cooling of gouge the difference in healing between subseismic slip rates delayed and rapid healing and seismic slip rates immediate and rapid healing suggests that the dominant weakening mechanism shifts from tribochemical processes at subseismic slip rates to frictional heating at seismic slip rates slip zone structures are too complex and variable from run to run to reveal microscopic mechanisms for the strength recovery rapid healing following seismic slip can be a cause for reduced aftershocks along major coseismic faults

systematic variations in recurrence interval and moment of repeating aftershocks 1 the recurrence intervals for 194 repeating clusters on the calaveras fault follow a power law decay relation with elapsed time after the 1984 m6 2 morgan hill california mainshock the decay rates of repeating aftershocks in the immediate vicinity of a high slip patch that failed during the mainshock systematically exceed those that are farther away the trend between relative moment and recurrence interval which is a measure of the fault healing rate varies systematically with depth and changes from negative to positive value as the distance between the repeating aftershock and the mainshock slip patch increases we speculate that high strain rate in the early postseismic period may cause transient embrittlement and strengthening of the deep repeating clusters in the areas adjacent to the mainshock slip patch resulting in large moments that decrease with time as the strain rate diminishes our observations suggest that systematic behavior of repeating aftershocks reflect variations in the fault zone rheology

characterisation of a fractured reservoir using microearthquakes induced by hydraulic injections abstract microseismic activity is induced by a number of engineering activities which involve fluid injection or extraction in naturally fractured rock masses evidence collected during the last 15 years of hot dry rock hdr geothermal energy research has clearly indicated the very strong positive correlation between induced microearthquake locations and fluid flow paths within the fractured rock mass microseismic monitoring is now used regularly in hdr research as the only effective means of mapping hydraulic stimulations and monitoring hydromechanical processes during operation of the fractured reservoir many of the techniques that have been developed through hdr research are directly applicable to the hydrocarbon industry for the monitoring of hydraulic fracturing treatments waterflood operations and reservoir depletion this paper provides a brief introduction to the hydromechanical interactions that result in induced microseismicity and presents case studies from three european hdr sites where the monitoring of microseismic activity has proved vital in targeting production wells mapping the progress of stimulation and waterfloods and understanding the hydromechanical behaviour of the fractured system

nonlinear strain buildup and the earthquake cycle on the san andreas fault two contrasting models of the earthquake deformation cycle on strike slip faults predict significant temporal declines in shear strain rate near the fault accompanied by a progressive broadening of the zone of deformation adjacent to it in the thin lithosphere model transient deformation results from flow in the asthenosphere due to stress relaxation following faulting through most or all of the lithosphere for an earth model with a thick elastic lithosphere plate thickness depth of seismic slip transient motions are due to postearthquake aseisrnic slip below the coseismic fault plane data from the san andreas fault indicate a long term temporal decrease in strain rate that persists for at least 30 years and may extend through the entire earthquake cycle observations support a cycle long rate decrease and a temporal spreading of the deformation profile only if movement cycles on the northern and southern locked sections of the fault are basically similar if so the usually lower strain rates and broader deformation zone currently observed on the southern san andreas represent a later evolutionary stage of the northern locked section where a great earthquake is a more recent occurrence although the data allow some extreme models to be discarded no sufficiently strong constraints exist to decide between the thin and thick lithosphere models regardless of the appropriate model the geodetic observations themselves indicate that strain buildup is sufficiently nonlinear to cause significant departures from recurrence estimates based on linear strain accumulation and the time predictable model

long term evolution of intraplate seismicity in stress shadows after a megathrust abstract megathrusts produce large permanent lithospheric displacements as well as strong transient ground shaking up to regional distances the influence of the 2011 m9 0 tohoku oki earthquake on the seismicity in stable intraplate regions around the korean peninsula is investigated the differential lateral displacements by the megathrust build transient radial tension field over the backarc lithosphere constructing stress shadows for all types of faults in optimal orientation over the wide backarc region including the southern korean peninsula a characteristic seismic velocity decrease after the megathrust supports the medium relaxation the number of earthquakes with magnitudes greater than or equal to 2 5 was increased by 61 after the megathrust the earthquakes occurred episodically a series of unusual earthquake swarms and a temporal cluster of moderate size earthquakes were observed in the yellow sea region the significant seismicity increase since the megathrust may be due to the fluid diffusion during the transient tension field and the pore fluid pressure increase during the ambient compressional stress field recovery by tectonic loading the induced seismicity may continue until the ambient stress field is fully recovered

late eocene impact ejecta geochemical and isotopic connections with the popigai impact structure late eocene microtektites and crystal bearing microkrystites extracted from dsdp and odp cores from the atlantic pacific and indian oceans have been analyzed to address their provenance a new analysis of nd and sr isotopic compositions confirms previous work and the assignment of the uppermost microtektite layer to the north american tektites which are associated with the 35 5 ma 85 km diameter chesapeake impact structure of virginia usa extensive major element and nd and sr isotopic analyses of the microkrystites from the lowermost layer were obtained the melanocratic microkrystites from sites 216 and 462 in the indian and pacific oceans possess major element chemistries sr and nd isotopic signatures and sm nd t chur model ages similar to those of tagamite melt rocks in the popigai impact structure they also possess rb sr t ur model ages that are younger than the tagamite t chur ages by up to 1 ga which require a process as yet undefined of rb sr enrichment these melanocratic microkrystites are consistent with a provenance from the 35 7 ma 100 km diameter popigai impact structure of siberia russia while ruling out other contemporaneous structures as a source melanocratic microkrystites from other sites and leucocratic microkrystites from all sites possess a wide range of isotopic compositions 143 nd values of 16 to 27 7 and 87 sr values of 4 1 354 0 making the association with popigai tagamites less clear these microkrystites may have been derived by the melting of target rocks of mixed composition which were ejected without homogenization dark glass and felsic inclusions extracted from popigai tagamites possess 143 nd and 87 sr values of 26 7 to 27 8 and 374 7 and 432 4 respectively and t chur and t ur model ages of 1640 1870 ma and 240 1830 ma respectively which require the preservation of initially present heterogeneity in the source materials the leucocratic microkrystites possess diverse isotopic compositions that may reflect the melting of supra basement sedimentary rocks from popigai or early basement melts that were ejected prior to homogenization of the popigai tagamites the ejection of melt rocks with chemistries consistent with a basement provenance rather than the surface 1 km of sedimentary cover rocks atypically indicates a non surficial source to some of the ejecta microkrystites from two adjacent biozones possess statistically indistinguishable major element compositions suggesting they have a single source the occurrence of microkrystites derived from a single impact event but in different biozones can be explained by 1 diachronous biozone boundaries 2 post accumulation sedimentary reworking or 3 erroneous biozonation

preseismic rupture progression and great earthquake instabilities at plate boundaries we present a procedure for modeling the initially quasi static upward progression of a zone of slip from some depth in the lithosphere toward the earth s surface along a transform plate margin culminating in a great crustal earthquake stress transmission in the lithosphere is analyzed with a generalized elsasser model in which elastic lithospheric plates undergo plane stress deformation and are coupled by an elementary foundation model to a maxwellian viscoelastic asthenosphere upward progression of rupture over a finite length of plate boundary corresponding to a seismic gap along strike is analyzed by a method based on the line spring concept whereby a two dimensional antiplane analysis of the upward progression provides the relation between lithospheric thickness averaged stress and slip used as a boundary condition in the generalized elsasser plate model the formulation results in a nonlinear integral equation for the rupture progression as a function of time and distance along strike a simpler approximate single degree of freedom analysis procedure is described and shown to lead to instability results that can be formulated in terms of the slip softening slope at the boundary falling below the elastic unloading stiffness of the surroundings the results also indicate a delay of ultimate seismic instability due to the stiffer short versus long time asthenospheric response and predict a final period of self driven creep toward instability the procedures for prediction of rupture progression and instability are illustrated in detail for an elastic brittle crack model of slip zone advance and parameters of the model are chosen consistently with great earthquake slips and stress drops for example an effective crack fracture energy of the order 4 106 j m2 at the peak 7 to 10 km below surface of a gaussian bell shaped distribution of fracture energy with depth with variance of the order 5 km simulating strength build up in a seismogenic layer leads to prediction of nominal seismic stress drops of 30 to 60 bars and slips of 2 to 5 m in great strike slip earthquake ruptures breaking 100 to 400 km along strike precursory surface straining in the self driven stage is predicted to proceed at a distinctly higher rate over time intervals beginning 3 to 10 months before such an earthquake this interval being greater for longer distances along strike over which the preseismic upward rupture progression takes place

biomass preservation in impact melt ejecta meteorites can have played a role in the delivery of the building blocks of life to earth only if organic compounds are able to survive the high pressures and temperatures of an impact event although experimental impact studies have reported the survival of organic compounds there are uncertainties in scaling experimental conditions to those of a meteorite impact on earth and organic matter has not been found in highly shocked impact materials in a natural setting impact glass linked to the 1 2 km diameter darwin crater in western tasmania is strewn over an area exceeding 400 km2 and is thought to have been ejected by a meteorite impact about 800 kyr ago into terrain consisting of rainforest and swamp here we use pyrolysis gas chromatography mass spectrometry to show that biomarkers representative of plant species in the local ecosystem including cellulose lignin aliphatic biopolymer and protein remnants survived the darwin impact we find that inside the impact glass the organic components are trapped in porous carbon spheres we propose that the organic material was captured within impact melt and preserved when the melt quenched to glass preventing organic decomposition since the impact we suggest that organic material can survive capture and transport in products of extreme impact processing at least for a darwin sized impact event

petrology and geochemistry of target rocks from the bosumtwi impact structure ghana and comparison with ivory coast tektites the 10 5 km diameter bosumtwi crater in ghana west africa is the most likely source crater for the ivory coast tektites as the tektites and the crater have the same age 1 07 ma and there are close similarities between the isotopic and chemical compositions of the tektites and crater rocks the crater is excavated in 2 1 2 2 ga old metasediments and metavolcanics of the birimian supergroup here we present the first integrated petrographic and geochemical study of rocks from the bosumtwi impact crater a variety of target rocks from the bosumtwi impact structure were selected to represent the major rock types that have been described before resulting in four groups shale phyllite graywacke and two different types of granites from dispersed dikes and from the so called pepiakese intrusion at the northeastern side of the crater these rocks were analyzed for their major and trace element composition and their petrographic characteristics in addition representative samples were also analyzed for their o sr and nd isotopic compositions the target rocks do not show any unambiguous evidence of shock metamorphism i e planar deformation features pdfs distinct impact characteristic shock effects pdfs were identified only in clasts within suevite derived melt fragments the compositional range of the target rocks is significantly wider than that of the ivory coast tektites but overlap the tektite compositions a best fit line for the bosumtwi crater rocks in a rb sr isotope evolution diagram yields an age of 1 98 ga and an initial 87sr 86sr ratio of 0 701 which is close to results previously obtained for granitoid intrusions in the birimian of ghana our nd isotopic data yield depleted mantle model ages ranging from 2 16 to 2 64 ga and nd values of 17 2 to 25 9 harmonic least squares hmx mixing calculations were able to reproduce the composition of ivory coast tektites from a mixture of bosumtwi country rocks that include about 70 phyllite graywacke 16 granite dike and 14 pepiakese granite the oxygen isotopic composition of the metasedimentary rocks and granite dikes 18o 11 3 13 6 and the tektites 18o 11 7 12 9 also this work agree fairly well while the pepiakese granites have lower values 18o 8 6 9 0 indicating that only minor amounts of these rocks were incorporated in the formation of the ivory coast tektites the large variation in sr and nd isotopic compositions of the target rocks do not allow the unambiguous identification of distinct endmember compositions but in both a 87sr 86sr vs 1 sr plot and an sr vs nd diagram the tektites plot within the area occupied by the metasedimentary and granitic bosumtwi crater rocks thus our data support the interpretation that the composition of the ivory coast tektites is similar to that of rocks exposed at the bosumtwi impact structure indicating formation during the same impact event

challenging the rate state asperity model afterslip following the 2011 m9 tohoku oki japan earthquake 1 prior to the 2011 m9 tohoku oki earthquake subduction at the japan trench was characterized by m7 8 earthquakes sometimes rupturing the same source regions seismic asperities followed by extensive afterslip detected by gps measurements a physically based model consisting of velocity weakening asperities surrounded by aseismic creep on velocity strengthening regions the rate state asperity model became the prevailing conceptual model for earthquakes in this region theory and numerical simulation indicates that velocity weakening areas do not exhibit sustained afterslip while velocity strengthening regions do not accumulate stress interseismically here we demonstrate that the rate state asperity model is contradicted by models of postseismic deformation following the tohoku oki earthquake afterslip in the first eight months either occurred on historical seismic asperities or stress accumulated in regions surrounding the asperities unsmoothed inversions of cumulative 8 month postseismic gps displacements that restrict afterslip to areas outside of historical ruptures cannot fit the data without afterslip exceeding the slip that fully relaxes the coseismic stress change in contrast similarly constrained inversions allowing slip within historical ruptures can satisfactorily fit the postseismic displacements these results require a modification of the rate state asperity model and raise new questions about physical processes and properties of the subduction interface

mechanics of seismic instabilities induced by the recovery of hydrocarbons we review earthquake distributions associated with hydrocarbon fields in the context of pore pressure diffusion models poroelastic stress transfer and isostasy theory these three mechanisms trigger or induce seismic instabilities at both local scale d 5 km and at regional scale d 20 km the modeled changes in stress are small 1 mpa whatever the tectonic setting each mechanism corresponds to different production processes 1 local hydraulic fracturing due to fluid injection induces seismic slip on cracks ml 3 within the injected reservoir through decreasing the effective stress 2 pure fluid withdrawal causes pore pressure to decrease within the reservoir it triggers adjustments of the geological structure to perturbations related to the reservoir response to depletion poroelastic mechanisms transfer this stress change from the reservoir to the surrounding levels whereml 5 seismic instabilities occur either above or below the reservoir 3 massive hydrocarbon recovery induces crustal readjustments due to the removal of load from the upper crust it can induce larger earthquakes ml 6 at greater distance from the hydrocarbon fields than the two other mechanisms

heat treated stone artifacts at shuidonggou northwest china and their archaeological implications artifacts from the shuidonggou sdg site complex in ningxia province provide extensive information and insights regarding the activities of early modern humans in china based on a series of experiments and physical analyses it appears that the stone artifacts from sdg locality 2 and locality 12 have undergone heat treatment that enhanced the utilization ratio and knapping properties of the lithic raw material from which they were made in order to investigate the mechanisms involved compression tests and xrd x ray diffraction examinations were conducted on lithic raw materials collected surround the sdg sites the results indicate that the heated stones present lower compression strength and better ductility and the raw material becomes more homogeneous as well the process of crack propagation also becomes easier to control thereby reducing knapping difficulties the application of heat treatment technology at sdg reflects the production capacities and risk management strategies of the sdg inhabitants and provides evidence for the level of understanding associated with early modern human behavior this discovery confirms the appearance of this technology in the east asia around 32 ka bp which lasts to 11 ka bp providing new evidence for the spread and distribution of heat treatment technology

mechanical characterization of raw material quality and its implication for early upper palaeolithic moravia abstract raw material mechanical tests were conducted to answer the question whether differences in raw material procurement among early upper palaeolithic populations in moravia czech republic may have been driven by different mechanical properties of those materials characterization of mechanical properties of erratic flints and krumlovsk les i type chert show that the relatively finer grained erratic flints preferred by local aurignacian populations are more easily and probably also predictably knapped at higher speeds such as reached with soft antler wood percussors whereas cherts of krumlovsk les i type exploited by both szeletian and aurignacian populations are more resistant to fracture propagation this implies the suitability of the former material for fine blade and bladelet production and of the latter to projectile e g szeletian leaf points manufacture and possibly explains the export of leaf points from szeletian areas the krumlov forest to bohunician and aurignacian sites within moravia exploitation of erratic flints was easier as regards aurignacian and probably entire upper palaeolithic knapping technology certain tasks however were better met with other raw materials thus reflecting the relativity of chipped stone raw material quality perception in the palaeolithic

heat treatment of polish flints abstract in poland three types of flint chocolate spotted and banded were intensively mined from the terminal palaeolithic to the early bronze age although heating of flint to improve its flaking properties was practised across the world from 110 000 years ago to the recent particularly in southwestern europe heat treatment of flint in poland is known from only two sites experimental studies showed that controlled heat treatment of polish flints causes subtle variable changes in colour but a consistent marked increase in lustre on fractured surfaces which should make heat treated artefacts easy to recognise in the polish archaeological record heat treatment also causes a substantial reduction in the fracture toughness of all tested polish flint types and a concomitant increase in flakeability the effect is greatest for banded flint due to its initially higher fracture toughness the decrease in fracture toughness is caused by recrystallisation allowing fractures to propagate more easily in banded flint the average crystal size increases and within chocolate and spotted flint the fibrous chalcedony patches become more granular although the flaking properties of banded flint are improved markedly by heat treatment the procedure was applied only occasionally by prehistoric flintknappers to this material banded flint was preferentially used for completely polished axes and only rarely for blades because chocolate and spotted flints are available close to the banded flint mines these flint types have far superior flaking properties and were extensively used for blade manufacture spotted flint is generally less suitable for heat treatment it is subject to explosive thermal spalling due to its abundant calcite inclusions although heat treatment improves the flaking properties of chocolate flint heated chocolate flint is rare in the polish archaeological record probably because high quality flint was so abundant in poland

the effect of loading rate on static friction and the rate of fault healing during the earthquake cycle the seismic cycle requires that faults strengthen heal between earthquakes and the rate of this healing process plays a key role in determining earthquake stress drop1 2 3 4 rupture characteristics5 6 and seismic scaling relations2 3 4 7 frictional healing as evidenced by increasing static friction during quasi stationary contact between two surfaces1 8 9 10 11 12 is considered the mechanism most likely to be responsible for fault strengthening2 3 13 14 previous studies however have shown a large discrepancy between laboratory and seismic field estimates of the healing rate2 3 4 14 15 in the laboratory rock friction changes by only a few per cent per order of magnitude change in slip rate whereas seismic stress drop increases by a factor of 2 to 5 per order of magnitude increase in earthquake recurrence interval but in such comparisons it is assumed that healing and static friction are independent of loading rate here i summarize laboratory measurements showing that static friction and healing vary with loading rate and time as expected from friction theory16 17 18 applying these results to seismic faulting and accounting for differences in laboratory seismic and tectonic slip rates i demonstrate that post seismic healing is expected to be retardedfor a period of several hundred days following an earthquake in agreement with recent findings from repeating earthquakes13 14 19 20

seismic triggering by rectified diffusion in geothermal systems widespread seismicity was triggered by the june 28 1992 landers california earthquake at a rate which was maximum immediately after passage of the exciting seismic waves rectified diffusion of vapor from hydrothermal liquids and magma into bubbles oscillating in an earthquake can increase the local pore pressure to seismically significant levels within the duration of the earthquake in a hydrothermal system modeled as a two component h 2o co 2 fluid in porous rock the pressure initially increases linearly with time the rate of pressure buildup depends sensitively on the mean bubble radius and is large for small bubbles the diffusion induced pressure is relaxed by percolation and resorption of vapor into the liquid solution the induced seismicity itself also relieves stress values of parameters used in the present calculations give results consistent with observations of triggered seismicity at long valley caldera after the landers earthquake for one representative condition at 250 c and 5 6 km depth oscillating strain acting on 10 m diameter bubbles increases pore pressure at the rate of 151 pa s resulting in a pressure increase of 12 kpa in the 80 s duration of the landers earthquake the elevated pressure induced by a single 26 m diameter cloud of bubbles in saturated rock relaxes by percolation through soil of 0 2 mdarcy permeability in 53 6 hours observations of earthquake swarms at other locations suggest that self induced buildup of pore pressure by rectified diffusion can provide a positive feedback mechanism for amplifying seismicity

geochemistry of darwin impact glass and target rocks abstract we have analyzed the major and trace element composition of 18 darwin glass samples and 7 target rocks sandstones shales and a quartzite from the darwin crater area on the basis of our data and using statistical methods 3 chemically distinct groups of darwin glass were identified a low fe al lfe al or average darwin glass group b hfe al group and c hmg na group the glasses of group c also show anomalous enrichments of several elements e g cr mn co and ni electron microprobe studies show that the glasses are inhomogeneous on the micrometer scale which is typical for impact glasses the geochemistry of all glasses is very similar to terrestrial sediments and thus supports the impact origin model we have performed mixing calculations which show that in general darwin glass can be formed by melting and mixing local target rocks the best fit is obtained for a mixture of 30 quartzite 60 shale b3 dg and 10 shale b1 dg some major element contents do not agree exactly which is most probably due to the limited selection of target rocks that were available for our study the analyses and mixing models demonstrate that volatile elements e g zn ga sb and the alkalies have been lost during production of the impact glasses which can be expected because of the high formation temperature we have furthermore tried to explain the enrichments of cr mn co and ni in group c glasses by contributions from a non sedimentary source e g ultrabasic rocks or from the impacting body none of the mixtures provides a satisfactory fit darwin glass does not show any significant ir enrichments admixture of material from iron meteorites gives too high fe co and ni and too low cr and mn contents chondritic contaminations would yield ir abundances in the glass that are several orders of magnitude above the observed levels better fits are obtained for an achondritic contamination but again give excess ir an ultrabasic contribution gives better results except for higher mg but no such rocks are known from the target area thus at the present time we are not able to explain the enrichments of cr mn co and ni in glasses of group c in a satisfactory way

slow and fast ruptures on a laboratory fault controlled by loading characteristics recent geodetic observations indicate that a single fault may slip slowly and silently or fast and seismically in different circumstances we report laboratory experiments that demonstrate how the mode of faulting can alternate between fast stick slip events 70 to 500 mm s sliding rates and slow silent events 0 001 to 30 mm s as a result of loading conditions rather than friction properties or stiffness of the loading machine the 760 mm long granite sample is close to the critical nucleation length scale for unstable slip so small variations in nucleation properties result in measurable differences in slip events slow events occur when instability cannot fully nucleate before reaching the sample ends dynamic events occur after long healing times or abrupt increases in loading rate which suggests that these factors shrink the spatial and temporal extents of the nucleation zone arrays of slip strain and ground motion sensors installed on the sample allow us to quantify seismic coupling and study details of premonitory slip and afterslip we find that seismic coupling decreases when slip rates fall below about 70 mm s the slow slip events we observe are primarily aseismic less than 1 of the seismic coupling of faster events and produce swarms of very small m 6 to m 8 events these mechanical and seismic interactions suggest that faults with transitional behavior where creep small earthquakes and tremor are often observed could become seismically coupled if loaded rapidly either by a slow slip front or dynamic rupture of an earthquake that nucleated elsewhere

earthquake aftereffects and triggered seismic phenomena the physical basis for delayed aftereffects of large crustal earthquakes is analyzed these effects apparently range in scale from typical aftershocks near the source region of a prior earthquake to the triggering of groundwater and deformation related anomalies possibly including other large earthquakes at locations as much as a few hundred kilometers from the source of a great earthquake observational reports of such aftereffects are reviewed and possible mechanisms for their occurrence are discussed

heating of flint debitage from upper palaeolithic contexts at manot cave israel changes in atomic organization due to heating using infrared spectroscopy abstract the heat treatment of flint is known to change its mechanical properties and improve its fracture behaviour during knapping here we examine 20 flint artifacts from upper paleolithic contexts from manot cave israel using fourier transform infrared spectroscopy and compare them to geogenic flint beds from the walls inside the cave and from outcrops just above the cave we show that the 512 and 467 cm 1 peaks are broader in most of the flint debitage pieces as compared to the geogenic flint and that broadening of these peaks occurs when geogenic flint from the cave wall is heated we also present an empirical simple method to monitor these changes

post seismic relaxation and earthquake triggering in the southern adriatic region summary an attempt at quantifying post seismic relaxation triggered by decoupling earthquakes along the eastern thrusting border of the adriatic plate southern dinarides is carried out by finite element modelling with a model constituted by an elastic lithosphere riding on a viscous asthenosphere in particular it is investigated the possibility that the above phenomenon is responsible for the fact that in the last two centuries most major earthquakes in the southern dinarides ms 6 have been followed within a few years by intense mainly tensional earthquakes in southern italy i e the zone lying on the opposite margin of the adriatic plate this analysis has been applied to the last example of the supposed seismic interrelation i e the triggering 1979 april 15 montenegro event ms 6 7 and the presumably induced 1980 november 23 irpinia earthquake in the southern apennines ms 6 9 results indicate that the strain induced in the southern apennines by the triggering event has significant amplitude since it largely exceeds the effect of earth tides and the principal stress axes are consistent with those of southern apenninic earthquakes the order of magnitude of the time delay between the montenegro and irpinia events 1 6 yr could be explained by assuming that earthquake triggering is most probable when the highest values of the induced strain rate reach the southern apennines in particular this interpretation predicts the observed time delay when a model diffusivity of 400 m2 s 1 is assumed the constraints that this diffusivity value may pose on the structural and rheological features of the crust upper mantle system in the study area are discussed it is shown that the effects of the montenegro event on the present velocity field are comparable to though systematically lower than the velocities suggested by geodetic observations in the italian region this suggests that geodynamic interpretations of geodetic data given without taking into account possible transient effects on the kinematic pattern as those related to post seismic relaxation may be incorrect experiments carried out by tentatively simulating the presence of subducted lithosphere along the western margin of the adriatic plate as a lateral variation of diffusivity have shown that this structural feature may emphasize e w tensional strains in the southern apennines

aftershock patterns and main shock faulting we have compared aftershock patterns following several moderate to large earthquakes with the corresponding distributions of coseismic slip obtained from previous analyses of the recorded strong ground motion and teleseismic waveforms well located aftershock hypocenters are projected onto the main shock fault plane and their positions are examined relative to the zones of coseismic displacement indicated by the estimated distributions of main shock slip we also examine the aftershock focal mechanisms when these data are available in an attempt to identify possible patterns of secondary faulting within the aftershock zone our results are consistent with a hypothesis of aftershock occurrence that requires a secondary redistribution of stress following primary failure on the earthquake fault aftershocks following the earthquakes examined in this study occur mostly outside of or near the edges of the source areas indicated by the patterns of main shock slip the spatial distribution of aftershocks reflects either a continuation of slip in the outer regions of the areas of maximum coseismic displacement or the activation of subsidiary faults within the volume surrounding the boundaries of main shock rupture

modeling afterslip and aftershocks following the 1992 landers earthquake one way to probe the rheology of the lithosphere and fault zones is to analyze the temporal evolution of deformation following a large earthquake in such a case the lithosphere responds to a known stress change that can be assessed from earthquake slip models constrained from seismology and geodesy here we model the postseismic response of a fault zone that is assumed to obey a rate strengthening rheology where the frictional stress varies as a ln e e being the deformation rate and a 0 a rheological parameter the model is simple enough that these parameters can be estimated by inversion of postseismic geodetic data we apply this approach to the analysis of geodetic displacements following the m w 7 3 1992 landers earthquake the model adjusts well the measured displacements and implies a 0 47 0 53 mpa in addition we show that aftershocks and afterslip follow the same temporal evolution and that the spatiotemporal distribution of aftershocks is consistent with the idea that they are driven by reloading of the seismogenic zone resulting from frictional afterslip

real time test of the long range aftershock algorithm as a tool for mid term earthquake prediction in southern california result of the algorithm of earthquake prediction published in 1982 is examined in this paper the algorithm is based on the hypothesis of long range interaction between strong and moderate earthquakes in a region it has been applied to the prediction of earthquakes withm 6 4 in southern california for the time interval 1932 1979 the retrospective results were as follows 9 out of 10 strong earthquakes were predicted with average spatial accuracy of 58 km and average delay time the time interval between a strong earthquake and its best precursor 9 4 years varying from 0 8 to 27 9 years during the time interval following the period studied in that publication namely in 1980 1988 four earthquakes occurred in the region which had a magnitude ofm 6 4 at least in one of the catalogs caltech or noaa three earthquakes coalinga of may 1983 chalfant valley of july 1985 and superstition hills of november 1987 were successfully predicted by the published algorithm

contemporary plate motion and crustal deformation the measurement of relative plate velocities during the past few years is a signal accomplishment in earth science leading to refinement of the precepts of steady motion of plate interiors and cyclic deformation along plate margins regrettably deformation premonitory to an earthquake has yet to be detected with confidence delineation of the spatial and temporal buildup of strain between earthquakes however has put limits on models of the earthquake cycle a diverse set of fault structures and crustal rheologic conditions can explain the pattern of surface strain accumulation and release along strike slip faults in contrast the geometry of thrusts and normal faults revealed by earthquake deformation has been found to differ markedly from expectations geodetic observations have proved vital to monitor the ascent of magma through the earth s crust and to predict volcanic eruptions at the earth s surface episodic vertical and horizontal deformation in southern california remains a subject of dispute if anything it is less certain than it once seemed

postseismic response of repeating aftershocks the recurrence intervals of repeating earthquakes on the san andreas fault in the loma prieta aftershock zone follow the characteristic 1 t decay of omori s law a model in which these earthquakes occur on isolated patches of the fault that fail in stick slip with creep around them can explain this observation in this model the recurrence interval is inversely proportional to the loading rate due to creep logarithmic velocity strengthening friction predicts 1 t decay in creep rate following the mainshock the time dependence of recurrence is inconsistent with a simple viscous constitutive relationship which predicts an exponential decay of loading rate thus our observations imply postseismic slip at seismogenic depth under a power law rheology the time dependence of postseismic deformation measured geodetically may be diagnostic of whether postseismic deformation is caused by creep or possible viscoelastic deformation at greater depths

the middle pleistocene site of la cansaladeta tarragona spain stratigraphic and archaeological succession abstract la cansaladeta is a site located in a narrow passage dug out by the francoli river in the pre littoral catalan range ne iberia the archaeological deposit lies on top of a 45 50 m fluvial terrace and contains a rich middle pleistocene stratigraphic succession in which 10 archaeological layers have been identified here we present the description of the sedimentary succession of the site the available chronological framework including tl tt osl and esr u series ages as well as biostratigraphical information the characteristics of the lithotechnical and faunal assemblages as well as the first interpretation of the human occupations at the site three main occupation phases have been differentiated the oldest archaeological layers are embedded in a palaeosol formed on a clayey layer that contains limestone fragments detached from the shelter s wall and roof during the second phase low energy fluvial sediments coming from lateral river floods were deposited and sealed the archaeological layers after a transitional phase the upper layers appear to be derived from slope sediments numerical dating yielded internally consistent dates of 380 400 ka for the sequence however the study of the fossil assemblages potentially suggest a tentative early middle pleistocene age for the lowermost horizons the rich technological record is made up of several local raw materials especially chert but also schist quartzite quartz and other minor rocks knapping sequences seem to be autochthonous as all the elements and size categories of the reduction sequence are present and refits are common techno typological features observed along the sequence are not very diagnostic however the lower layers include some acheulean forms among the large shaped tools restricted variability among the small retouched tools mostly denticulates and a virtually absence of prepared cores the faunal assemblage is scarce and appears strongly altered only the lower layers have provided fruitful information although neither combustion areas nor structures related to fire use have been documented to date heat damage has been repeatedly recorded on both lithic and faunal remains this may point to systematic fire use within the archaeological sequence the data provided by the ongoing excavations at la cansaladeta provide new insight into the early human settlement history of northeast iberia to be reconstructed combining these data with those coming from the close site of barranc de la boella enable us to better reconstruct the timing nature and context of early human occupation in the region