paraglacial rock slope stability glaciation and deglaciation along with their associated climatic and non climatic processes modify slope stresses and influence slope stability paraglacial slope failures are those that are a part of or influenced by the transition from glacial conditions to non glacial conditions gravitational failure of rock slopes is a primary and dominant process of slope evolution in mountainous terrain and is the subject of this paper which 1 reviews the approaches taken for researching paraglacial rock slope failure patterns and processes 2 summarises the spatial and temporal patterns of post glacial failures 3 assesses the factors influencing slope stability during glaciation and deglaciation 4 explores some of the applications of paraglacial research and 5 highlights some of the outstanding issues to be resolved and provides recommendations for terminology relating to paraglacial slope processes

complete dynamic modeling calibration for the thurwieser rock avalanche italian central alps abstract few rock avalanches have been witnessed and no exact real time description is available the 2 5 m m 3 punta thurwieser rock avalanche september 2004 italian central alps is a unique event for which many quantitative observations have been gathered this is the first case ever of a natural rock avalanche being recorded on video and for which an almost exact value of the total time duration from initial detachment to final deposition is available the landslide travelled over 2 9 km from its source partially in a glacial environment the initial failure and the time for the complete evacuation of the source area were studied and assessed by a series of photos the mean front velocities along the path have been estimated from the video the final geometry and the characteristics of the deposit have been obtained by gps measurements aerial photos field surveys and laboratory tests a quasi 3d continuum dynamic analysis of the landslide motion has been performed assuming both a voellmy and a frictional rheology in the model dan 3d for the first time the landslide front velocities have been used for back analyses and calibration of the rheological parameters together with the final shape and thickness of the deposit and its developing extension the dynamic flow resistance parameters initially calibrated with dan were adopted and validated in dan 3d showing good consistency they are consistent with the existing database for calibrated landslides of similar type and scale flow velocities on the path segment underlain by glacial deposits up to 55 65 m s 1 are more accurately predicted by adopting a frictional rheology up to 50 55 m s 1 with zero pore pressure and a 26 friction angle than by a voellmy rheology up to 40 45 m s 1 both observations and modelling show that glacial ice plays a substantial role in increasing the rock avalanche mobility

microseismicity on patches of higher compression during larger scale earthquake nucleation in a rate and state fault model while many large earthquakes are preceded by observable foreshocks the mechanism responsible for the occurrence of these smaller scale seismic events remains uncertain one physical explanation of foreshocks with growing support is that they are produced by the interaction of slow slip with fault heterogeneity inspired by the suggestion from laboratory experiments that foreshocks occur on fault asperities bumps we explore rate and state fault models with patches of higher normal stress embedded in a larger seismogenic region by conducting 3 d numerical simulations of their behavior over long term sequences of aseismic and seismic slips the models do produce smaller scale seismicity during the aseismic nucleation of larger scale seismic events these smaller scale events have reasonable stress drops despite the highly elevated compression assigned to the source patches we find that the two main factors contributing to the reasonable stress drops are the significant extent of the rupture into the region surrounding the patches and the aseismic stress release just prior to the seismic events the smaller scale seismicity can only occur if a sufficient separation in nucleation scales between the foreshock like events and mainshocks is achieved our modeling provides insight into the conditions conducive for generating foreshocks on both natural and laboratory faults

why permafrost rocks become unstable a rock ice mechanical model in time and space in this paper we develop a mechanical model that relates the destabilisation of thawing permafrost rock slopes to temperature related effects on both rock and ice mechanics and laboratory testing of key assumptions is performed degrading permafrost is considered to be an important factor for rock slope failures in alpine and arctic environments but the mechanics are poorly understood the destabilisation is commonly attributed to changes in ice mechanical properties while bedrock friction and fracture propagation have not been considered yet however fracture toughness compressive and tensile strength decrease by up to 50 and more when intact water saturated rock thaws based on literature and experiments we develop a modified mohr coulomb failure criterion for ice filled rock fractures thatincorporates fracturing of rock bridges friction of rough fracture surfaces ductile creep of ice and detachment mechanisms along rock ice interfaces novel laboratory setups were developed to assess the temperature dependency of the friction of ice free rock rock interfaces and the shear detachment of rock ice interfaces indegrading permafrost rock mechanical properties may control early stages of destabilisation and become more important for higher normal stress i e higher magnitudes of rock slope failure ice mechanical properties outbalance the importance of rock mechanical components after the deformation accelerates and are more relevant for smaller magnitudes the model explains why all magnitudes of rock slope failures can be prepared and triggered by permafrost degradation and is capable of conditioning long paraglacial response times here we present a synoptic rock and ice mechanical model that explains the mechanical destabilisation processes operating in warming permafrost rocks

coseismic interferograms of two ms 6 6 earthquakes in the south iceland seismic zone june 2000 we present insar observations of deformation due to two ms 6 6 earthquakes in the south iceland seismic zone in june 2000 coseismic deformation predominates in the ers interferograms range change due to mainly right lateral strike slip on n s striking faults amounting to more than 15 cm is observed although displacement is mainly perpendicular to the satellite look direction using elastic dislocation models in a trial and error scheme we find a best fitting model that agrees well with the aftershock locations and moment magnitudes estimated from seismograms the june 17 model has a fault patch 16 km long 10 km deep striking n05 e dipping 86 with a slip maximum of 2 40 m the june 21 model has a vertical patch 15 km long 9 km deep striking n01 w with a slip maximum of 2 15 m

coseismic stress changes and crustal deformation on the reykjanes peninsula due to triggered earthquakes on 17 june 2000 1 a large mw 6 5 earthquake struck the south iceland seismic zone sisz on 17 june 2000 the 17 june main shock triggered increased seismicity over a large area and significant slip on at least three distinct faults on the reykjanes peninsula up to 87 km to the west of the event a second large mw 6 4 earthquake in the sisz occurred on 21 june 2000 about 17 km west of the 17 june main shock this event does not appear to have triggered as much activity on the reykjanes peninsula as the 17 june main shock although the epicenter was closer crustal deformation signals due to the june 2000 earthquakes on the reykjanes peninsula were observed with campaign and continuous gps and synthetic aperture radar interferometry with the largest coseismic deformation signal near lake kleifarvatn we model the faults using three uniform slip rectangular dislocations in an elastic half space best fit uniform slip models consistent with seismic and geodetic data indicate that all three faults trend n s and the motion on them was primarily right lateral strike slip our study suggests that the event near kleifarvatn had a significantly larger moment than seismic estimates indicating a component of aseismic slip on the fault lasting no more than several hours static coulomb failure stress change calculations indicate that the event at kleifarvatn increased the coulomb stress at the hypocenter of the nupshlidarhals event by 0 1 0 2 mpa as well as loading the hvalhnukur fault

quake catalogs from an optical monitoring of an interfacial crack propagation using an experimental setup which allows to follow optically the propagation of an interfacial crack front in a heterogeneous medium we show that the fracture front dynamics is governed by local and irregular avalanches with large velocity fluctuations events defined as high velocity bursts are ranked in catalogs with analogous characteristics to seismicity catalogs time of occurence epicenter location and energy parameter moment despite differences in the fracturing mode opening for the experiments and shear rupture for earthquakes in the acquisition mode and in the range of time scales the distributions of moment and epicenter jumps in the experimental catalogs obey the same scaling laws with exponents similar to the corresponding distributions for earthquakes the record breaking event analysis also shows very strong similarities between experimental and real seismicity catalogs the results suggest that the dynamics of crack propagation is controlled by the elastic interactions between microstructures within the material

the 2002 denali fault earthquake alaska a large magnitude slip partitioned event the mw moment magnitude 7 9 denali fault earthquake on 3 november 2002 was associated with 340 kilometers of surface rupture and was the largest strike slip earthquake in north america in almost 150 years it illuminates earthquake mechanics and hazards of large strike slip faults it began with thrusting on the previously unrecognized susitna glacier fault continued with right slip on the denali fault then took a right step and continued with right slip on the totschunda fault there is good correlation between geologically observed and geophysically inferred moment release the earthquake produced unusually strong distal effects in the rupture propagation direction including triggered seismicity

contrasting zoning profiles in high grade garnets evidence for the allochthonous nature of a grenville province terrane in the central part of the grenville province proterozoic metasediments of the reservoir cabonga terrane arc underlain by gently dipping archean migmatites a major mylonite zone located within the migmatites is the base of a large thrust sheet made up of the reservoir cabonga terrane and a migmatitic sole garnets from meta aluminous assemblages in proterozoic metasediments mylonites and migmatites display contrasting types of ca zoning patterns garnets with ca rich cores are found along the western edge of the reservoir cabonga terrane whereas garnets with flat ca profiles are found in the remaining proterozoic metapelites in the mylonites and in the archean migmatites considering samples in which an infinite reservoir of ca ions is warranted by abundant plagioclase in the matrix pressures well in excess of 1200 mpa at temperatures between 700 and 800 c are indicated for a metamorphic event recorded in the cores of garnets from the western edge of the reservoir cabonga terrane the inner rim of garnet records pressures of around 1000 mpa for the same temperature range in homogeneous garnets a single p t set around 800 mpa and 750 c is recorded in the migmatites some of the mylonites initiate their recrystallization under relatively high pressures which is continued during decompression and record the lowest p t values these metamorphic signatures suggest that the proterozoic metapelites were already metamorphosed under relatively high pressure when emplaced on to archean migmatites and that the entire area was subsequently subjected to metamorphism at a lower pressure

a new observation of dynamically triggered regional seismicity earthquakes in greece following the august 1999 izmit turkey earthquake the m w 7 4 izmit turkey earthquake triggered widespread regional seismicity in greece over a study region extending from 400 km to nearly 1000 km away from the epicenter small events began immediately after the passage of the mainshock surface waves suggesting that the transient stresses of the seismic waves were the trigger the increase in cataloged earthquakes in ordinary continental crust is a new observation and is statistically significant at the 95 level unlike the previous example of distant triggering during the landers earthquake the activated seismicity occurred entirely in non volcanic areas the greek sites were triggered by waves with amplitudes at least a factor of 3 lower than the observed triggering threshold for imperial valley we speculate that dynamic triggering on a regional scale results in countrywide episodes of increased seismicity or superswarms in regions with low triggering thresholds such as greece

remotely triggered microearthquakes at the geysers geothermal field california microearthquake meq activity recorded on a local network at the geysers geothermal field has been observed to increase dramatically within seconds to minutes after the arrival of surface waves from large regional earthquakes this behavior was observed not only following the 1992 landers earthquake for which remotely triggered seismicity at the geysers and elsewhere has been documented but also for the following events gulf of alaska ms 7 6 march 6 1988 loma prieta ms 7 1 october 17 1989 two events within the gorda plate ms 6 9 on july 13 1991 and ms 7 1 on august 17 1991 petrolia ms 7 0 april 25 1992 and northridge m s 6 6 january 17 1994 the exact onset times of most swarms are difficult to pinpoint but all start within minutes of the passage of seismic waves and in at least one case gulf of alaska the onset appears to coincide with the expected arrival of the surface waves these swarms generally last for a few hours at most and decay with time in a manner similar to aftershock sequences we propose that the dynamic stresses associated with seismic waves emanating from these earthquakes may trigger the onset of these swarms the landers event may have been particularly efficient at generating remotely triggered swarms throughout the western u s because of its size and shallow focal depth which would promote large surface waves our data demonstrate however that the phenomenon is not unique to the landers event

modelling instantaneous dynamic triggering in a 3 d fault system application to the 2000 june south iceland seismic sequence summary we present a model of seismogenesis on an extended 3 d fault subject to the external perturba tions of coseismic stress changes due to an earthquake occurring on another fault the causative fault as an application we consider the spatio temporal stress redistribution produced on the hvalhnukur fault by the m s 6 6 2000 june 17 mainshock in the south iceland seismic zone sisz the latter is located nearly 64 km from the causative fault and failed 26 s after the main shock with an estimated magnitude m w 5 25 0 25 providing an example of instantaneous dynamic triggering the stress perturbations are computed by means of a discrete wavenumber and reflectivity code the response of the perturbed fault is then analysed solving the truly 3 d fully dynamic or spontaneous problem accounting for crustal stratification in a previous study the response of the hvalhnukur fault was analysed by using a spring slider fault model ss fault model comparing the estimated perturbed failure time with the observed origin time in addition to the perturbed failure time this model can provide numerical estimates of many other dynamic features of the triggered event which can be compared with available observations the rupture history of the whole fault plane its final extent and the seismic mo ment of the induced event we show the key differences existing between a mass spring model and this extended fault model in particular we show the essential role of the load exerted by the neighbouring slipping points of the fault by considering both rate and state dependent laws and non linear slip dependent law we show how the dynamics of the 26 s fault strongly depend on the assumed constitutive law and initial stress conditions in the case of rate and state dependent friction laws assuming an initial effective normal stress distribution that is suitable for the sisz and consistent with previously stated conditions of instantaneous dynamic triggering of the hvalhnukur fault we obtain results in general agreement with observations

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

crustal deformation measured by gps in the south iceland seismic zone due to two large earthquakes in june 2000 two large earthquakes struck the south iceland seismic zone in june 2000 the first on june 17 mw 6 5 and the second on june 21 mw 6 4 these are the largest earthquakes in the area in the past 88 years a network of gps stations was remeasured followingthe earthquakes the whole network was last measured in 1995 and partly in 1999 we correct for the interseismic motion from 1995 to 2000 to obtain the coseismic displacements the largest co seismic motion we observe is about 0 55 m in the epicentral area of the june 17 event we model the surface deforma tion for the two earthquakes usingrectang ular dislocations in an elastic half space best fit uniform slip models indi cate that the events occurred on two parallel n s vertical faults with right lateral strike slip motion this is the same style of faultingbelieved to have occurred in larg e historical earthquake sequences in south iceland

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

near lithostatic pore pressure at seismogenic depths a thermoporoelastic model summary a model is presented for pore pressure migration through a transition layer separating a meteoric aquifer at hydrostatic pressure from a deeper reservoir at lithostatic pressure this configuration is thought to be pertinent to the south iceland seismic zone sisz and to other tectonically active regions of recent volcanism where volatiles are continuously released by ascending magma below the brittle ductile transition poroelastic parameters are computed for basaltic rock the model is 1 d the fluid viscosity is temperature dependent and rock permeability is assumed to be pressure dependent according to a dislocation model of a fractured medium environment conditions are considered pertinent to basalt saturated with water at shallow depth case i and at mid crustal depth case ii if the intrinsic permeability of the rock is high no significant effects are observed in the pressure field but advective heat transfer shifts the brittle ductile transition to shallower depths if the intrinsic permeability is low the pressure dependent permeability can propagate near lithostatic pore pressures throughout most of the transition layer while the temperature is practically unaffected by advective contributions so that the rock in the transition layer remains in brittle condition geometrical parameters characterizing the fracture distribution are important in determining the effective permeability in particular if an interconnected system of fractures develops within the transition layer the effective permeability may increase by several orders of magnitude and near lithostatic pore pressure propagates upwards these modelling results have important bearings on our understanding of seismogenic processes in geothermal areas and are consistent with several geophysical observations in the sisz in connection with the two 2000 june m 6 5 earthquakes including i fluid pressure pulses in deep wells ii low resistivity at the base of the seismogenic layer iii low vp vs ratio and time dependent seismic tomography iv heterogeneity of focal mechanisms v shear wave splitting vi high b value of deep foreshocks vii triggered seismicity and viii radon anomalies

geodetic and seismologic evidence for slip variability along a blind normal fault in the umbria marche 1997 1998 earthquakes central italy summary we analysed elevation changes induced by the 1997 1998 umbria marche central apennines italy earthquakes we employed data from a first order geodetic levelling line measured in 1951 1992 and 1998 the line bears a record of pre seismic and coseismic strains associated with the causative fault of the 1997 september 26 09 40 mainshock mw 6 0 a first level analysis performed under the assumption of slip homogeneity of coseismic slip shows misfits that cannot be reduced simply by altering the fault size and geometry a more detailed analysis based on a distribution of coseismic slip obtained from broad band seismograms provides a better fit and is in agreement with 1951 1992 elevation changes interpreted as precursory slip by previous investigators the levelling data sets new constraints on the location extent dip and depth of the fault in full agreement with seismological evidence and images from sar interferometry the data show no evidence for slip in the uppermost 3 km of the crust suggesting that a major and widely recognized normal fault that exists in the area is no longer active and showing a tendency of present tectonic strains to revert the current topographic setting

the failure of earthquake failure models in this study i show that simple heuristic models and numerical calculations suggest that an entire class of commonly invoked models of earthquake failure processes cannot explain triggering of seismicity by transient or dynamic stress changes such as stress changes associated with passing seismic waves the models of this class have the common feature that the physical property characterizing failure increases at an accelerating rate when a fault is loaded stressed at a constant rate examples include models that invoke rate state friction or subcritical crack growth in which the properties characterizing failure are slip or crack length respectively failure occurs when the rate at which these grow accelerates to values exceeding some critical threshold these accelerating failure models do not predict the finite durations of dynamically triggered earthquake sequences e g at aftershock or remote distances some of the failure models belonging to this class have been used to explain static stress triggering of aftershocks this may imply that the physical processes underlying dynamic triggering differs or that currently applied models of static triggering require modification if the former is the case we might appeal to physical mechanisms relying on oscillatory deformations such as compaction of saturated fault gouge leading to pore pressure increase or cyclic fatigue however if dynamic and static triggering mechanisms differ one still needs to ask why static triggering models that neglect these dynamic mechanisms appear to explain many observations if the static and dynamic triggering mechanisms are the same perhaps assumptions about accelerating failure and or that triggering advances the failure times of a population of inevitable earthquakes are incorrect

evidence of instantaneous dynamic triggering during the seismic sequence of year 2000 in south iceland 1 we analyze the coseismic stress perturbation during the 17 june 2000 south iceland seismic sequence the main shock ms 6 6 was followed by three large events within a few tens of seconds 8 26 and 30 s located within 80 km the aim of this paper is to investigate short term fault interaction and instantaneous triggering this happens when a fault perturbed by a stress change fails before the end of the transient stress perturbation we compute the shear normal and coulomb stress changes as functions of time in a stratified elastic half space by using discrete wave number and reflectivity methods we calculate dynamic stresses caused by the main shock at the hypocenters of these three subsequent events our numerical results show that the onset of the last two events is slightly delayed with respect to the arrival time of the second positive peak of coulomb stress variation while the first event occurred after the first positive stress peak we have also analyzed the response of a spring slider system representing a fault governed by a rate and state dependent friction law perturbed by shear and normal stress variations caused by the main shock the fault response to the computed stress perturbations is always clock advanced we have found suitable constitutive parameters of the modeled fault that allow the instantaneous dynamic triggering of these three earthquakes if the initial sliding velocity is comparable with the tectonic loading velocity we obtained failure times close to the observed origin times for low values of the initial effective normal stress

indication of high pore fluid pressures in a seismically active fault zone summary polarisations of seismic shear wave splitting observed above small earthquakes in iceland are typically approximately ne to sw parallel to the direction of maximum horizontal stress in contrast the polarisations of shear waves at three new stations sited over the husav ik flatey fault a major seismically active transform fault in northern iceland are approximately nw to se orthogonal to the stress aligned polarisations elsewhere modelling suggests that these 90 flips in polarisations are caused by propagation through cracks containing fluids at high pore fluid pressures within one or two mpa of the critical stress these observations suggest that high pore fluid pressures which play a key role in earthquake source mechanisms can be monitored by analysing shear wave splitting above seismically active fault planes

three dimensional earthquake sequence simulations with evolving temperature and pore pressure due to shear heating effect of heterogeneous hydraulic diffusivity 1 a new methodology for three dimensional 3 d simulations of earthquake sequences is presented that accounts not only for inertial effects during seismic events but also for shear induced temperature variations on the fault and the associated evolution of pore fluid pressure in particular the methodology allows to capture thermal pressurization tp due to frictional heating in a shear zone one dimensional 1 d diffusion of heat and pore fluids in the fault normal direction is incorporated using a spectral method which is unconditionally stable accurate with affordable computational resources and highly suitable to earthquake sequence calculations that use variable time steps the approach is used to investigate the effect of heterogeneous hydraulic properties by considering a fault model with two regions of different hydraulic diffusivities and hence different potential for tp we find that the region of more efficient tp produces larger slip in model spanning events the slip deficit in the other region is filled with more frequent smaller events creating spatiotemporal complexity of large events on the fault interestingly the area of maximum slip in model spanning events is not associated with the maximum temperature increase because of stronger dynamic weakening in that area the region of more efficient tp has lower interseismic shear stress which discourages rupture nucleation there contrary to what was concluded in prior studies seismic events nucleate in the region of less efficient tp where interseismic shear stress is higher in our model hypocenters of large events do not occur in areas of large slip or large stress drop

on the deterministic description of earthquakes 1 the quantitative estimate of earthquake damage due to ground shaking is of pivotal importance in geosciences and its knowledge should hopefully lead to the formulation of improved strategies for seismic hazard assessment numerical models of the processes occurring during seismogenic faulting represent a powerful tool to explore realistic scenarios that are often far from being fully reproduced in laboratory experiments because of intrinsic technical limitations in this paper we discuss the prominent role of the fault governing model which describes the behavior of the fault traction during a dynamic slip failure and accounts for the different and potentially competing chemical and physical dissipative mechanisms we show in a comprehensive sketch the large number of constitutive models adopted in dynamic modeling of seismic events and we emphasize their prominent features limitations and specific advantages in a quantitative comparison we show through numerical simulations that spontaneous dynamic ruptures obeying the idealized linear slip weakening sw equation and a more elaborated rate and state dependent friction law produce very similar results in terms of rupture times peaks slip velocity developed slip and stress drops provided that the frictional parameters are adequately comparable and more importantly that the fracture energy density is the same our numerical experiments also illustrate that the different models predict fault slip velocity time histories characterized by a similar frequency content a feeble predominance of high frequencies in the sw case emerges in the frequency ranges 0 3 1 and 11 50 hz these simulations clearly indicate that even forgiving the frequency band limitation it would be very difficult virtually impossible to discriminate between two different but energetically identical constitutive models on the basis of the seismograms recorded after a natural earthquake

electrical resistivity tomography monitoring of permafrost in solid rock walls 1 this article describes the first attempt to conduct electrical resistivity tomography ert in solid permafrost affected rock faces electrode design instrument settings and processing routines capable of measuring under relevant conditions were developed four transects with nw ne east e and south s aspects were installed in solid rock faces between matter valley and turtmann valley switzerland at 3070 3150 m above sea level dc resistivity in the transects was measured repeatedly during the summer and compared by applying a time lapse inversion routine resistivity values were calibrated using observed rock surface conditions of thawed damp rocks 1 8 k m deeply frozen rocks 18 80 k m and the transition from damp thawed to frozen rocks 8 18 k m mean surface layer resistivities of transects respond to air temperatures below 0 c with a rapid increase by a factor of 1 4 to 2 9 from values of 12 15 k m to values of 22 31 k m rock layers at depths of 2 6 m display a general trend of resistivity decrease in summer corresponding to a persistent thawing process their response to anomalously cool august temperatures occurs with a time lag of 2 to 4 weeks only transects e ne and nw display persistent high resistivity permafrost bodies 50 k m mostly at depths of 6 10 m the maximum thaw depth of a continuous thawing front above permafrost is 6 m however the ert results emphasize the role of heat transfer by deep reaching cleft water systems thus permafrost occurs in lenses rather than layers ert provides rapid detection of ice and water distribution in permafrost affected bedrock

coulomb stress changes in the south iceland seismic zone due to two large earthquakes in june 2000 1 the south iceland seismic zone experienced the largest earthquakes for 88 years in june 2000 with a ms 6 6 event on june 17 followed by another ms 6 6 earthquake on june 21 these events occurred on two parallel n s striking right lateral strike slip faults separated by about 17 km we calculate the static coulomb stress change for the june 17 and 21 earthquakes using a distributed slip model derived from joint inversion of insar and gps data we find that the static stress change caused by the june 17 event is about 0 1 mpa at the location of the june 21 hypocenter promoting failure on the second fault locations of aftershocks agree well with areas of increased coulomb failure stress our calculations indicate that positive stress changes due to the two earthquakes make the area west of the june 21 rupture the most likely site of the next large earthquake in south iceland

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

dynamic versus static stress triggering and friction parameters inferences from the november 23 1980 irpinia earthquake this paper concentrates on the problem of fault interaction and earthquake triggering through the 1980 irpinia italy sequence more specifically this paper deals with the problem of the triggering of the second subevent by the mainshock the interaction between the two segments is modeled through a dynamic coulomb failure function the aims of this paper are first to discriminate between the dynamic and the static stress effects on the triggering if these effects exist second to estimate the fault strength relative to the initial state of stress third to determine the parameters of a slip dependent friction law that lead to the observed delay of 20 s numerical simulations show that the critical slip dc may range from 0 03 m up to 1 7 m and that the initial slope of the friction law 0 must be lower than 0 04 m 1 we show that the relative magnitude of the fault strength and the initial state of stress govern the existence and value of a dc lower threshold under which the fault always ruptures before 13 s a close to failure fault is not consistent with a critical slip dc less than 0 8 m whereas small values of dc typically 0 03 m imply a far from failure fault general results concern the effect of a dynamic stress pulse we show that an event can be triggered by a transient stress pulse and that in this case the event can have an initiation duration much longer than the pulse duration we show that it is possible to explain both the triggering and the time delay only with the effect of the transient stress pulse this may explain aftershock triggering even in regions of negative coulomb failure function or long distance triggering of earthquakes by propagating waves

direct observation of frost wedging in alpine bedrock width and temperature of rock joints were automatically monitored in the japanese alps three years of monitoring on a sandstone rock face shows two seasonal peaks of joint widening in autumn and spring the autumn events are associated with short term freeze thaw cycles and the magnitude of widening reflects the freezing intensity and water availability the short term freezing can produce wedging to a depth of at least 20 cm the spring events follow a rise in the rock surface temperature to 0 c beneath the seasonal snowcover and likely originate from refreezing of meltwater entering the joint some of these events contribute to permanent enlargement of the joint two other joints on nearby rock faces experience only sporadic widening accompanying freeze thaw cycles and insignificant permanent enlargement observations indicate that no single thermal criterion can explain frost weathering the temperature range at which wedging occurs varies with the bedrock conditions water availability and duration of freezing copyright 2001 john wiley sons ltd

effects of permeability and porosity evolution on simulated earthquakes numerical simulations are a fundamental tool to access the typical conditions attained during earthquake instabilities and to simulate the large number of dissipative processes taking places during faulting in this study we consider a single degree of freedom spring slider system a simplified fault model which can describe the whole seismic cycle and the dynamics of a fault with spatially homogeneous properties we assume a rate and state dependent friction in which we incorporate the effects of pore fluid pressure thermally pressurized as a consequence of the frictional heat produced during sliding we explore in a single framework the role of the time variations of the porosity permeability or both ultimately leading to changes in hydraulic diffusivity which has been recognized as one of the key parameters in thermally pressurized faults our synthetic ruptures show that the changes in the hydraulic diffusivity only due to porosity variations do not markedly affect the earthquake recurrence cycle time the traction evolution and the thermal history of the fault on the contrary when the evolutions of both the porosity and the permeability are accounted for the cycle time is significantly reduced this result has a clear implication in the context of the hazard assessment

experimental design for a pilot study on bedrock weathering near the permafrost table an experimental design is described to test the hypothesis that ice segregation near the top of permafrost and in the lower part of the active layer can brecciate frost susceptible bedrock seasonal temperature cycles in the active layer and the top of permafrost were simulated to a first approximation within a block of chalk measuring 30 m 31 m wide and 33 m high and insulated around the sides to minimize lateral heat transfer the block moistened first by capillary rise was initially frozen from the surface downwards simulating permafrost aggradation thereafter the upper half of the block was cycled above and below 0 c simulating seasonal freezing and thawing of the active layer while the lower half remained below 0 c simulating permafrost during thaw cycles water was supplied to the surface and base of the simulated active layer temperature unfrozen water content surface frost heave and porewater pressure within the chalk were monitored during the experiment

what can physical source models tell us about the recurrence time of earthquakes abstract earthquake prediction no matter what the timescale has been and continues to be a contentious subject and it is indubitably a prominent challenge for modern seismology and earthquake physics indeed few natural events can have the catastrophic consequences of earthquakes earthquakes today account for about 60 of natural fatalities a physical description of an earthquake represents an amenable approach to the prediction but it suffers of some limitations basically due to the notorious ignorance about the initial state of a given fault and about the physical law controlling its traction evolution independent on those intrinsic epistemic limitations the concept of the earthquake recurrence based upon the idea of the cyclic or characteristic earthquake has been often invoked to describe and thus to predict subsequent instability events on a seismogenic structure in this paper by using the simplest analog fault model the one degree of freedom mass spring system we quantitatively show that the concepts of the recurrence time and the earthquake cycle have limitations even making them meaningless we will discuss in a compendious synopsis all the possible physical mechanisms which can dramatically affect the recurrence time our conclusions emphasize again that the competing mechanisms potentially occurring during faulting even in the simplest and idealized condition of an isolated fault can significantly complicate the regular cyclicity of earthquakes predicted by the analog fault system these conclusions can contribute to the debate about the role of the physical modeling of earthquakes in the contest of seismic hazard assessment

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

a constitutive scaling law and a unified comprehension for frictional slip failure shear fracture of intact rock and earthquake rupture 1 it is widely recognized that some of the physical quantities inherent in a rupture are scale dependent and the scale dependence is one of the most no facts and features of rupture phenomena the paper addresses how such scale dependent shear rupture of a broad range from laboratory scale frictional slip failure and shear fracture of intact rock to field scale rupture as an earthquake source can be unified by a single constitutive law noting that the earthquake rupture is a mixed process between frictional slip failure and the shear fracture of intact rock it is concluded that the constitutive law for the earthquake rupture be formulated as a unifying law that governs both frictional slip failure and shear fracture of intact rock it is demonstrated that the slip dependent constitutive law is such a unifying law and a constitutive scaling law is derived from laboratory data on both frictional slip failure and shear fracture of intact rock this constitutive scaling law enables one to provide a consistent and unified comprehension for scale dependent physical quantities inherent in the rupture over a broad range from small scale frictional slip failure and shear fracture in the laboratory to large scale earthquake rupture in the field

effects of supershear rupture speed on the high frequency content of s waves investigated using spontaneous dynamic rupture models and isochrone theory 1 in this paper we achieve three goals 1 we demonstrate that crack tips governed by friction laws including slip weakening rate and state dependent laws and thermal pressurization of pore fluids propagating at supershear speed have slip velocity functions with reduced high frequency content compared to crack tips traveling at subshear speeds this is demonstrated using a fully dynamic spontaneous three dimensional earthquake model in which we calculate fault slip velocity at nine points locations distributed along a quarter circle on the fault where the rupture is traveling at supershear speed in the in plane direction and subshear speed in the antiplane direction this holds for a fault governed by the linear slip weakening constitutive equation by slip weakening with thermal pressurization of pore fluid and by rate and state dependent laws with thermal pressurization the same is also true even assuming a highly heterogeneous initial shear stress field on the fault 2 using isochrone theory we derive a general expression for the spectral characteristics and geometric spreading of two pulses arising from supershear rupture the well known mach wave and a second lesser known pulse caused by rupture acceleration 3 we demonstrate that the mach cone amplification of high frequencies overwhelms the de amplification of high frequency content in the slip velocity functions in supershear ruptures consequently when earthquake ruptures travel at supershear speed a net enhancement of high frequency radiation is expected and the alleged low peak accelerations observed for the 2002 denali and other large earthquakes are probably not caused by diminished high frequency content in the slip velocity function as has been speculated

dynamic modeling of the 1992 landers earthquake we have used observed band pass filtered accelerograms and a previously determined slip distribution to invert for the dynamic rupture propagation of the 1992 landers earthquake in our simulations dynamic rupture grows under the simultaneous control of initial stress and rupture resistance by friction which we modeled using a simple slip weakening law we used a simplified landers fault model where the fault segments were combined into a single vertical planar fault by trial and error we modified an initial stress field inferred from the kinematic slip distribution proposed by wald and heaton 1994 until dynamic rupture generated a rupture history and final slip distribution that approximately matched those determined by the kinematic inversion we found that rupture propagation was extremely sensitive to small changes in the distribution of prestress and that a delicate balance with energy release rate controls the average rupture speed for the inversion we generated synthetic 0 5 hz ground displacements using an efficient green s function propagator method axitra this method enables us to propagate the radiation generated by the dynamic rupture to distances greater than those feasible using the finite difference method the dynamic model built by trial and error inversion provides a very satisfactory fit between synthetics and strong motion data we validated this model using records from stations used in the slip inversion as well as some which were not included we also inverted for a complementary model that fits the data just as well but in which the initial stress was perfectly uniform while rupture resistance was heterogeneous this demonstrates that inversion of ground motion is nonunique

magnetotelluric survey across the active spreading zone in southwest iceland abstract the results of 10 magnetotelluric soundings performed along a 110 km long profile crossing the constructive plate boundary in southwest iceland are presented apparent resistivities are interpreted by a horizontally stratified earth model to yield a pseudo cross section along the profile the crust mantle interface contains a well conductive layer the depth to the good conductor increases with age of the crust and the distance from the axial zone this layer is interpreted as partially molten basalt at a temperature about 1100 c and a volume fraction of the melt phase in the range 10 20 the high conductivity layer probably disappears west of the borgarnes anticlinal axis which separates the older to the west and younger to the east flood basalts in western iceland indicating that the temperature below the oldest part of the profile lies below the solidus curve of basalt recent seismic crustal investigations in the same area indicate a state of partial melting or a magma chamber which agrees with the results of the magnetotelluric soundings

dynamic stress variations due to shear faults in a plane layered medium summary a complete set of expressions is presented for the computation of elastic dynamic stress in plane layered media we use a discrete wavenumber reflectivity method to compute the stress field radiated by arbitrary moment tensor sources the expressions derived here represent an interesting tool for both the observational and theoretical analysis of dynamic stress changes associated with earthquake phenomena dynamic stress changes associated with a strike slip fault having unilateral rupture are shown this modelling which is similar to the 1992 landers california earthquake illustrates the effects of distance directivity and depth on transient stress changes

pressures and hydrogeology in petroleum basins abstract in most deep sedimentary basins in the world there is a layered arrangement of at least two superimposed hydrogeological systems the shallowest hydrogeological system can extend to great depths however in many basins it extends from the surface down to only about 10 000 ft greatest historical depth of burial the shallow hydrogeological systems generally are basin wide in extent and exhibit normal pressures the pore water apparently is free to migrate approximately in accordance with the theory of fluid migration proposed by munn 1909 and quantified by hubbert 1940 and 1953 the deeper hydrogeological systems usually are not basin wide in extent and exhibit abnormal pressures they generally consist of a layer of individual fluid compartments which are sealed off from each other and from the overlying system in some basins mainly in the onshore u s there is an even deeper near normally pressured noncompartmented section the compartmented layer in those basins generally is in the sequence of rocks which were deposited during the period of most rapid deposition the underlying noncompartmented layer where present usually is in prebasin shelf deposits and basement rock the uppermost noncompartmented layer usually is in rocks which were deposited during the last 10 000 ft in basin filling correlations of petroleum in reservoirs with the rocks from which the petroleum was generated has imposed a system of mainly upwards paths for the first several thousand feet of migration of petroleum from source rocks largely within the compartmented layer to pools generally in the shallow hydrogeological system the migration paths of petroleum and water may not be coincident

modeling high stress drops scaling interaction and irregularity of repeating earthquake sequences near parkfield repeating earthquake sequences have been actively investigated to clarify many aspects of earthquake physics the two particularly well studied sequences known as the los angeles and san francisco repeaters have several intriguing observations including their long for the seismic moment recurrence times that would suggest stress drops of 300 mpa based on typical assumptions near syncronized timing prior to 2004 and higher than typical inferred stress drops of 25 to 65 mpa up to 90 mpa locally but not as high as the recurrence times suggest here we show that all these observations are self consistent in the sense that they can be reproduced in a single fault model the suitable models build on the standard rate and state fault models with velocity weakening patches imbedded into a velocity strengthening region by adding either enhanced dynamic weakening during seismic slip or elevated normal stress on the patches or both to allow for the higher stress drops such models are able to match the observed average properties of the san francisco and los angeles repeaters as well as the overall nontrivial scaling between the recurrence time and seismic moment exhibited by many repeating sequences as a whole for reasonable parameter choices based on experiments and theoretical studies these models are characterized by the occurrence of substantial and variable aseismic slip at the locations of the repeating sources which explains their atypical relation between recurrence interval and seismic moment induces variability in the repeating source properties as observed and results in their neither slip nor time predictable behavior

transient triggering of near and distant earthquakes we demonstrate qualitatively that frictional instability theory provides a context for understanding how earthquakes may be triggered by transient loads associated with seismic waves from near and distance earthquakes we assume that earthquake triggering is a stick slip process and test two hypotheses about the effect of transients on the timing of instabilities using a simple spring slider model and a rate and state dependent friction constitutive law a critical triggering threshold is implicit in such a model formulation our first hypothesis is that transient loads lead to clock advances i e transients hasten the time of earthquakes that would have happened eventually due to constant background loading alone modeling results demonstrate that transient loads do lead to clock advances and that the triggered instabilities may occur after the transient has ceased i e triggering may be delayed these simple clock advance models predict complex relationships between the triggering delay the clock advance and the transient characteristics the triggering delay and the degree of clock advance both depend nonlinearly on when in the earthquake cycle the transient load is applied this implies that the stress required to bring about failure does not depend linearly on loading time even when the fault is loaded at a constant rate the timing of instability also depends nonlinearly on the transient loading rate faster rates more rapidly hastening instability this implies that higher frequency and or longer duration seismic waves should increase the amount of clock advance these modeling results and simple calculations suggest that near tens of kilometers small moderate earthquakes and remote thousands of kilometers earthquakes with magnitudes 2 to 3 units larger may be equally effective at triggering seismicity our second hypothesis is that some triggered seismicity represents earthquakes that would not have happened without the transient load i e accumulated strain energy would have been relieved via other mechanisms we test this using two new seismicity models that 1 are inherently unstable but slide at steady state conditions under the background load and 2 are conditionally stable such that instability occurs only for sufficiently large perturbations for the new seismicity models very small amplitude transients trigger instability relative to the clock advance models the unstable steady state models predict that the triggering delay depends inversely and nonlinearly on the transient amplitude as in the clock advance models we were unable to generate delayed triggering with conditionally stable models for both new seismicity models the potential for triggering is independent of when the transient load is applied or equivalently of the prestress unlike in the clock advance models in these models a critical triggering threshold appears to be inversely proportional to frequency further advancement of our understanding will require more sophisticated quantitative models and observations that distinguish between our qualitative yet distinctly different model predictions

permafrost thaw and destabilization of alpine rock walls in the hot summer of 2003 1 exceptional rockfall occurred throughout the alps during the unusually hot summer of 2003 it is likely related to the fast thermal reaction of the subsurface of steep rock slopes and a corresponding destabilization of ice filled discontinuities this suggests that rockfall may be a direct and unexpectedly fast impact of climate change based upon our measurements in alpine rock faces we present model simulations illustrating the distribution and degradation of permafrost where the summer of 2003 has resulted in extreme thaw we argue that hotter summers predicted by climate models for the coming decades will result in reduced stability of many alpine rock walls

the kolka karmadon rock ice slide of 20 september 2002 an extraordinary event of historical dimensions in north ossetia russian caucasus on 20 september 2002 an enormous rock ice slide and subsequent mud flow occurred on the northern slope of the kazbek massif northern ossetia russian caucasus it started on the north northeast wall of dzhimarai khokh 4780 ma s l and seriously affected the valley of genaldon karmadon immediate governmental actions available scientific information first reconstructions hazard assessments and monitoring activities as well as initial expert judgments recommendations are documented in order to enable more detailed analyses and modelling of the event by the wider scientific community among the most remarkable aspects related to this event are 1 the relation between the recent event and somewhat smaller but quite similar events that occurred earlier in historical times 1835 1902 2 the interactions between unstable local geological structures and complex geothermal and hydraulic conditions in the starting zone with permafrost cold to polythermal hanging glaciers and volcanic effects hot springs in close contact with each other 3 the erosion and incorporation of a debris covered valley glacier largely enhancing the sliding volume of rocks ice firn snow water and probably air to a total of about 100 106m3 and 4 the astonishingly high flow velocities up to 300 km h 1 and enormous length of travel path 18 km plus 15 km of debris mud flow this extraordinary case illustrates that large catastrophic events in high mountain regions typically involve a multitude of factors and require integrated consideration of complex chains of processes a task which must be undertaken by qualified groups of experts

an efficient mechanism to avert frictional melts during seismic ruptures abstract we consider the spatio temporal evolution of temperature due to frictional heating caused by the spontaneous propagation of 3 d dynamic seismic ruptures on planar faults in our numerical experiments which characterize typical crustal earthquakes we assume that fault friction is controlled by different linear and nonlinear slip dependent friction laws in this paper we confirm that a necessary condition to prevent melting is to have a nearly complete breakdown stress drop our simulations which employ a nonlinear slip dependent governing equation recently inferred from laboratory experiments by sone and shimamoto 2009 reproduce such a dramatic fault weakening and represent a plausible explanation for the prevention of melting during earthquake ruptures we also demonstrate that low friction alone although necessary is not a sufficient condition to avert melts the linear or classical slip weakening sw law would produce melting even assuming the same lengthscales and frictional levels to avoid melting with linear sw law we have to impose a specific value of the sw distance this reveals the prominent role of the time evolution of traction within the cohesive zone where the stress release is realized and of the value of the fracture energy density

laboratory testing and parameters controlling the shear strength of filled rock joints the shear strength of iofilled rock joints has been studied for a long time but a complete understanding of the mechanisms and of the parameters controlling the process has never been reached this paper reviews test results in the literature and compares them with results obtained by the authors the main parameters controlling the shear strength of infilled joints are discussed and a framework for understanding the failure mechanisms involved in the shearing of such discontinuities is given la resistance au cisaillement des joints rocheux remplis a ete etudiee depuis tres longtemps mais le mecanisme et les parametres controlant le processus n ont jamais ete totalement compris cet article passe en revue les resultats des essais publies et les compare avec les resultats obtenus par les auteurs les parametres principaux controlant la resistance au cisaillement des joints remplis sont discutes et un cadre pour comprendre les mecanismes de rupture associes au cisaillement de telles discontinuites est donne

on the role of multiple interactions in remote aftershock triggering the landers and the hector mine case studies the observed seismicity rate increase after large earthquakes in sites that are located several source lengths away from the mainshock centroid poses a major problem this is because the static stress change induced by a mainshock in that region seems to be insignificant and the dynamic stress changes can only en hance the seismicity during the passage of the seismic waves but not at later times in quest for a physically viable triggering mechanism for delayed aftershocks in remote sites we examine earthquake activities in remote sites that were triggered by two california earthquakes the magnitude 7 1 hector mine earthquake and the mag nitude 7 3 landers earthquake we introduce a new method for quantifying the de gree to which the triggering effect of each aftershock is locally more important than the triggering effect of the mainshock we apply this method to the landers and the hector mine remote aftershock sequences we show that multiple stress transfers from early aftershocks to later aftershocks played an important role in the enhance ment of both the landers and the hector mine aftershock activities in remote sites we present a time space diagram of the hector mine remote aftershock sequence in the imperial valley which shows that this sequence is made up of several subse quences and that the onset of activity migrated southward

a unified model for dynamic and static stress triggering of aftershocks antishocks remote seismicity creep events and multisegmented rupture aftershocks have been thought to be triggered by static stress transfer the 1992 landers and 1999 hector mine california earthquakes have demonstrated the possibility of remote triggering of seismicity highlighting the role of dynamic seismic waves static stress changes and transient deformations have different timescales the mechanisms by which they trigger earthquakes are thought to be different leading to an unwieldy vision of aftershock triggering we propose a model that encompasses both static and dynamic triggering of aftershocks and antishocks as well as the occurrence of stable slip creep events or multisegmented rupture the framework of this model is based on the stability instability transition of faults we propose that dynamic and static stress triggering pertain to the same physical process we study the effect of the complete coulomb failure function we demonstrate the possibility of the triggering of seismicity by a dynamic stress pulse in a stress shadow zone characterized by a negative static stress field the limited time efficiency of dynamic triggering shown by the data is explained by the model we suggest that dynamic waves trigger only the most unstable faults associated with a relatively short characteristic time while the static stress field triggers also faults that are stable associated with a larger characteristic time

what does control earthquake ruptures and dynamic faulting a review of different competing mechanisms the fault weakening occurring during an earthquake and the temporal evolution of the traction on a seismogenic fault depend on several physical mechanisms potentially concurrent and interacting recent laboratory experiments and geological field observations of natural faults revealed the presence and sometime the coexistence of thermally activated processes such as thermal pressurization of pore fluids melting of gouge and rocks material property changes thermally induced chemical environment evolution elasto dynamic lubrication porosity and permeability evolution gouge fragmentation and wear etc in this paper by reviewing in a unifying sketch all possible chemico physical mechanisms that can affect the traction evolution we suggest how they can be incorporated in a realistic fault governing equation we will also show that simplified theoretical models that idealistically neglect these phenomena appear to be inadequate to describe as realistically as possible the details of breakdown process i e the stress release and the consequent high frequency seismic wave radiation quantitative estimates show that in most cases the incorporation of such nonlinear phenomena has significant often dramatic effects on the fault weakening and on the dynamic rupture propagation the range of variability of the value of some parameters the uncertainties in the relative weight of the various competing mechanisms and the difference in their characteristic length and time scales sometime indicate that the formulation of a realistic governing law still requires joint efforts from theoretical models laboratory experiments and field observations

kinematic models of plate boundary deformation in southwest iceland derived from gps observations 1 we use data from gps campaign and continuous measurements from 1992 to 2004 in sw iceland to map the surface velocity field from the reykjanes peninsula to the eastern volcanic zone we divide the time series into preseismic july 1992 to june 2000 and postseismic june 2000 to may 2004 time intervals and we estimate gps station velocities for each interval as well as coseismic offsets due to the june 2000 earthquake sequence in the south iceland seismic zone sisz in addition to the plate spreading the preseismic velocity field shows the effects of inflation at hengill and hekla volcanoes whereas the postseismic velocities show deformation following the june 2000 earthquakes we consider several kinematic models to explain the preseismic velocities our preferred model includes several dislocations and point sources in an elastic half space with left lateral slip along the plate boundary on the reykjanes peninsula and below the sisz opening across the reykjanes peninsula and the western and eastern rift zones the optimal model has a locking depth of about 8 km in the central and eastern part of the reykjanes peninsula with a deep slip rate of about 17 mm yr and an opening of about 9 mm yr this locking depth is in agreement with the thickness of the seismogenic crust on the reykjanes peninsula which appears to vary between 7 and 9 km for the sisz we obtain a deep slip rate of about 19 mm yr below 16 km depth which is considerably deeper than the earthquake hypocenter depths in the area

microseismicity simulated on asperity like fault patches on scaling of seismic moment with duration and seismological estimates of stress drops observations show that microseismic events from the same location can have similar source durations but different seismic moments violating the commonly assumed scaling we use numerical simulations of earthquake sequences to demonstrate that strength variations over seismogenic patches provide an explanation of such behavior with the event duration controlled by the patch size and event magnitude determined by how much of the patch area is ruptured we find that stress drops estimated by typical seismological analyses for the simulated sources significantly increase with the event magnitude ranging from 0 006 to 8 mpa however the actual stress drops determined from the on fault stress changes are magnitude independent and 3 mpa our findings suggest that fault heterogeneity results in local deviations in the moment duration scaling and earthquake sources with complex shapes of the ruptured area for some of which stress drops may be significantly 100 1 000 times underestimated by the typical seismological methods

temperature variations of constitutive parameters can significantly affect the fault dynamics abstract a rate and state dependent governing law with temperature dependent constitutive parameters is considered on the basis of laboratory inferences we model the whole seismic cycle of a homogeneous fault obeying to such a law by adopting a spring slider dashpot fault analog model we show that the variations of the parameter a accounting for the so called direct effect with the temperature cause the system to enter at high speeds in a conditionally stable regime and also in a velocity strengthening regime although we do not observe the complete cessation of slip we can see a severe reduction of the degree of the instability of the fault in particular the peaks of the sliding velocity are reduced as well as the developed temperature due to frictional sliding and the released stress during each instability event moreover the recurrence times are reduced of a factor of two with respect to a reference configuration where the canonical formulation of rate and state friction with temporally constant parameters is assumed the obtained results can help the interpretation of high velocities laboratory experiments and further illuminate the importance of the temperature in the context of seismic hazard assessment

surface effects of triggered fault slip on reykjanes peninsula sw iceland three large earthquakes mw 4 5 were triggered within 5 min 85 km west of a mw 6 5 earthquake in the south iceland seismic zone sisz we report on surface effects of these triggered earthquakes which include fresh rupture widespread rockfall disrupted rockslides and block slides field data confirm that the earthquakes occurred along n striking right lateral strike slip faults field data also support the conclusion from modeling of insar data that deformation from the second triggered event was more significant than for the other two a major hydrological effect was the draining of water through an open fissure on a lake bed lowering the lake level by greater than 4 m field relationships suggest that a component of aseismic slip could have been facilitated by water draining into the fault zone d 2003 elsevier science b v all rights reserved