time dependent postseismic slip following the 1978 m w 7 3 tabas e golshan iran earthquake revealed by over 20 years of esa insar observations abstract we use over 20 yrs 1996 2017 of the european space agency s esa radar interferometry insar observations to investigate the postseismic deformation of the tabas fold segment following the 1978 m w 7 3 tabas e golshan earthquake in eastern iran we generated maps of satellite line of sight los velocity using two ers descending tracks 1996 1999 one envisat descending track 2003 2010 one sentinel 1a descending track 2014 2017 and one sentinel 1a ascending track 2014 2017 the los velocity shows afterslip continuing for at least 40 yrs after the earthquake elastic dislocation modelling based on the insar measurements reveals a decrease in postseismic velocities from 5 0 0 8 mm yr in 1996 1999 to 3 9 0 6 mm yr in 2003 2005 3 0 0 4 mm yr in 2006 2010 and a present rate of 2 3 0 6 mm yr in 2014 2017 the rates decay with time t as 1 t consistent with the predictions of a simple block slider model we then combine the insar rates and our previous estimates of the total earthquake slip derived from optical image matching and dem differencing to explore the frictional behaviour of the tabas fold we obtained a rate and state parameter a b 0 003 indicating rate strengthening frictional behaviour of the tabas fault we also inferred a minimum coseismic slip of 4 7 m which might have driven bedding plane shear at shallow depth resulting in distributed fold growth and secondary faulting observed in the field the results imply that both coseismic slip and afterslip have occurred in the same location one possible mechanism to explain such a phenomenon is that the frictional parameter a b is small enough to allow dynamic ruptures to propagate into rate strengthening regions

pseudotachylite generated as a result of a drilling burn in abstract material similar to naturally occurring pseudotachylite was generated in proterozoic lava as a result of frictional overheating of a diamond drill dh 5000 impregnated crown at a depth of 2 4 km below surface bit rotation equation to slip rates of about 1 m s is thought to have caused severe overheating to last for 3 10 s estimates show that melting occurred in the temperature range 800 1100 c under wet conditions and at comparatively low effective normal and shear stresses of about 1 9 107 and 9 7 106 pa respectively associated breccia formed as a result of thermal decrepitation rather than dynamic comminution and as a corollary it is suggested that some cataclasites associated with pseudotachylite bearing faults may also form by the mechanism this implies that the presence of both cataclasite and pseudotachylite on a fault plane does not necessarily indicate reactivation

rheology of bubble bearing magmas the rheology of bubble bearing suspensions is investigated through a series of three dimensional boundary integral calculations in which the effects of bubble deformation volume fraction and shear rate are considered the behaviour of bubbles in viscous flows is characterized by the capillary number ca the ratio of viscous shear stresses that promote deformation to surface tension stresses that resist bubble deformation estimates of ca in natural lava flows are highly variable reflecting variations in shear rate and melt viscosity in the low capillary number limit e g in carbonatite flows bubbles remain spherical and may contribute greater shear stress to the suspension than in high capillary number flows in which bubble deformation is significant at higher ca deformed bubbles become aligned in the direction of flow and as a result contribute less shear stress to the suspension calculations indicate that the effective shear viscosity of bubbly suspensions at least for ca 0 5 is a weakly increasing function of volume fraction and that suspensions of bubbles are shear thinning field observations and qualitative arguments however suggest that for sufficiently large ca ca greater than about 1 the effective shear viscosity may be less than that of the suspending liquid bubbles reach their quasi steady deformed shapes after strains of order one for shorter times the continuous deformation of the bubbles results in continual changes of rheological properties in particular for small strains the effective shear viscosity of the suspension may be less than that of the liquid phase even for small ca results of this study may help explain previous experimental theoretical and field based observations regarding the effects of bubbles on flow rheology

experimental study for noble gas release and exchange under high speed frictional melting abstract isotope ratios of noble gases in certain minerals are believed to be modified easily by their ambient reservoirs when the minerals reach temperatures that are higher than their closure temperatures the thermal history of a rock or a geologic event even a fault movement can therefore be determined quantitatively by application of radiometric dating methods to different minerals however neither traditional k ar nor ar ar dating methods are readily applicable to faulted rocks because in the case of faulting it is difficult to prove that the temperature of an event was greater than the closure temperatures of minerals frictional melting experiments performed on fine grain homogeneous gabbroid with high temperatures induced by frictional heating using a high velocity friction apparatus were performed to test whether rapid fault movement can reset the noble gas isotope ratio of fault rocks the temperature on the artificial fault plane is much higher than the closure temperature of the k ar system as inferred from the calculated cooling age the anticipated rapid equilibration of volatiles during the frictional melting of rocks implies that the noble gas isotope composition ratio was reset to an atmospheric value during this experiment we measured noble gas isotopes in a gabbroid sample using laser fusion analysis the resetting of noble gases is only observed in glass that had melted completely rejuvenation and or apparent increases in the k ar ages were only observed in a narrow 3 mm wide zone around the fault plane which appears to be thermally altered and mechanically fractured in thin sections because of frictional heating such glassy materials called pseudotachylytes sometimes form along the fault plane in natural faults as a result of complete melting of rock induced by frictional heating thus these results suggest that k ar ages of fault activity can be quantitatively obtained from the analysis of pseudotachylytes

benthic foraminiferal response to changes in bottom water oxygenation and organic carbon flux in the eastern mediterranean during lgm to recent times abstract we present a high resolution study of benthic foraminiferal abundances in 4 cores from the central aegean and ne levantine seas spanning the interval from 30 ka bp to the present the benthic foraminiferal faunas indicate that during lgm times bottom waters were well ventilated while organic flux to the sea floor was significantly higher than today from 30 to 10 2 ka bp faunal density and composition suggest a gradual decrease in organic flux to the sea floor this trend is interrupted by a short return to higher organic flux levels during the younger dryas 12 8 11 5 ka bp the faunas immediately preceding the early to middle holocene organic rich layer sapropel s1 are very similar to late holocene faunas indicating oligotrophic conditions the transition from well ventilated bottom waters to anoxic levantine basin or strongly dysoxic aegean sea bottom waters appears to take place within a time span of only 600 years from 10 8 to 10 2 ka bp sapropel s1 10 2 6 4 ka bp is characterized by extended periods of bottom water anoxia in the levantine basin and by strongly dysoxic conditions punctuated by episodic re ventilation events in the aegean sea re establishment of fully oxygenated bottom water conditions after sapropel s1 was extremely rapid the ensuing late holocene faunas are very similar to recent faunas found in the aegean sea suggesting much lower fluxes of organic matter to the sea floor than during glacial times

experimental frictional heating of coal gouge at seismic slip rates evidence for devolatilization and thermal pressurization of gouge fluids high velocity 1 m s friction experiments on bituminous coal gouge display several earthquake related phenomena including devolatilization by frictional heating gas pressurization and slip weakening stage i is characterized by sample shortening and reduction in the coefficient of friction from 1 to 0 6 stage ii is characterized by high frequency 5 hz oscillations in stress and strain records and by gas emissions stage iii is marked by rapid weakening 0 1 to 0 35 and sample shortening together with continued gas emissions stage iv produces stable stress records and continued weakness 0 2 but without gas emission stage i shortening is due to compaction of the gouge and the weakening is attributed to mechanical or thermal effects stage ii behavior is interpreted as due to coal gasification and fluctuations in fluid pressure resulting in high frequency stick slip type behavior dramatic reduction in shear stress in stage iii is attributed to gas pressurization by pore collapse and corresponds to a frictional instability analogous to nucleation of an earthquake microstructural observations indicate the deformation was brittle during stages i and ii but ductile during stages iii and iv time dependent finite element frictional heat models indicate the center of the samples became hot 900 c during stage ii whereas the edge of samples remained relatively cold 300 c vitrinite reflectance of coal samples shows an increase in reflectance from 0 5 to 0 8 over the displacement interval 20 40 m 20 40 s indicating that the reflectance responds to frictional heating on a short time scale the energy expended per unit area in these low stress large displacement experiments is similar to that of higher stress 50 mpa short displacement 1 m earthquakes 107 j m2

selective melting processes as inferred from experimentally generated pseudotachylytes abstract high speed friction experiments have been conducted on gabbros and granites to better constrain the process of frictional melting during seismogenic fault motion experiments were done on cylindrical specimens of 25 mm in diameter under a normal stress of 1 0 1 5 mpa and at slip rates up to 2 m s using a rotary shear high speed frictional testing machine the experimentally generated pseudotachylytes consist of a fused glassy matrix with abundant vesicles and angular or sub angular to rounded fragments these locally occur as injected network veins in the fractured rock x ray diffraction analysis has revealed the presence of as much as 40 70 wt glass the mineral contents of clasts in the experimental pseudotachylyte in granite as determined by x ray diffraction analysis indicate that quartz is the most resistant to melting biotite the least and feldspar is intermediate thus the sio2 depletion in natural pseudotachylyte glass is likely to be due to the selective melting of constituent materials during frictional melting

earthquake source nucleation a physical model for short term precursors abstract ohnaka m 1992 earthquake source nucleation a physical model for short term precursors in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 149 178 this paper deals with a quasistatic leading to a quasidynamic at a later time nucleation process that precedes the earthquake dynamic rupture and models of the earthquake source nucleation are put forward based on physical principles a quasistatic to quasidynamic rupture nucleation process is an intrinsic part of the ensuing earthquake dynamic rupture in other words the nucleation process itself is an short term or immediate precursor that occurs in a localized zone during the earthquake nucleation premonitory slip proceeds in the localized nucleation zone and shear stress also decreases gradually in the zone since slip weakening occurs during the nucleation immediate foreshock activity is a part of the nucleation process leading to the mainshock dynamic rupture therefore hypocentral locations of foreshocks are necessarily restricted to lie near the mainshock hypocentre onset of the mainshock rupture whether or not foreshocks occur during the mainshock nucleation depends on how the rupture growth resistance varies on a local to small scale since patches of greater rupture growth resistance are considered to prevail on a local to small scale in the fault zone carrying immediate foreshocks would be one of the major characteristics of earthquakes that nucleate within the brittle seismogenic layer when a mainshock earthquake nucleates within the brittle seismogenic layer and its hypocentre is located near the base of the seismogenic layer immediate foreshocks for this mainshock are necessarily restricted to lie within a localized region shallower than hypocentral depth of the mainshock by contrast the nucleation process below the base of the seismogenic layer is aseismic in nature so that carrying no conspicuous foreshocks would be a common characteristic of interplate earthquakes that nucleate below the base of the brittle seismogenic layer the breakdown strength p the breakdown stress drop b and the critical slip displacement dc are indicative of the rupture growth resistance to estimate depth variations of these parameters the effects of the normal stress n and temperature t on those parameters are examined using available data so far published the combined effects of n and t on p in the brittle to semibrittle regime are found to be represented empirically by p n t po n 1 cosh 50 t 40 sinh 50 t exp 2000 t where po n 135 7 0 750 n and t is measured in k and n in mpa it is found that dc increases sharply with t but is insensitive to n above 300 c while dc depends on n but is insensitive to t below 300 c on the basis of these results variations in p dc and b at mid crustal depths are estimated for quartzo feldspathic rocks for a given geothermal gradient

winter spring flushing of bass strait south eastern australia a numerical modelling study this study investigates winter spring flushing of bass strait with a two dimensional non linear depth averaged shallow water model the model is driven with a 180 day wind time series an advection diffusion scheme for several tracers is used to reveal the flushing pattern timescale of the region the study considers how external water masses flush strait waters it shows that shelf water entering the strait through the passage between king island and cape grim makes the largest contribution to strait waters results show that the central area of the strait is a stagnation area of weak currents and long flushing times 160 days the influence of external water masses on the stagnation area is estimated the findings have implications for marine ecosystems residence times air sea modifications of water mass properties and dense water formation in the region

high velocity frictional properties of alpine fault rocks mechanical data microstructural analysis and implications for rupture propagation abstract the alpine fault in new zealand is a major plate bounding structure that typically slips in m8 earthquakes every c 330 years to investigate the near surface high velocity frictional behavior of surface and borehole derived alpine fault gouges and cataclasites twenty one rotary shear experiments were conducted at 1 mpa normal stress and 1 m s equivalent slip velocity under both room dry and water saturated wet conditions in the room dry experiments the peak friction coefficient p p n of alpine fault cataclasites and fault gouges was consistently high mean p 0 67 0 07 in the wet experiments the fault gouge peak friction coefficients were lower mean p 0 20 0 12 than the cataclasite peak friction coefficients mean p 0 64 0 04 all fault rocks exhibited very low steady state friction coefficients ss room dry experiments mean ss 0 16 0 05 wet experiments mean ss 0 09 0 04 of all the experiments performed six experiments conducted on wet smectite bearing principal slip zone psz fault gouges yielded the lowest peak friction coefficients p 0 10 0 20 the lowest steady state friction coefficients ss 0 03 0 09 and commonly the lowest specific fracture energy values e g 0 01 0 69 mj m 2 microstructures produced during room dry and wet experiments on a smectite bearing psz fault gouge were compared with microstructures in the same material recovered from the deep fault drilling project dfdp 1 drill cores the near absence of localized shear bands with a strong crystallographic preferred orientation in the natural samples most resembles microstructures formed during wet experiments mechanical data and microstructural observations suggest that alpine fault ruptures propagate preferentially through water saturated smectite bearing fault gouges that exhibit low peak and steady state friction coefficients

low frictional strength of quartz rocks at subseismic slip rates 1 laboratory experiments on rocks at low sliding velocity typically yield values of the friction coefficient of 0 6 0 85 here we demonstrate that an extraordinary decrease in friction coefficient accompanies sliding of room dry quartz rocks at rates faster than in most laboratory experiments but slower than seismic slip rates in some cases the friction coefficient decreases from low speed values by more than a factor of 3 this extraordinary weakening likely results from the formation of finely comminuted amorphous wet material on the sliding surface

viscosity determinations of some frictionally generated silicate melts implications for fault zone rheology at high strain rates analytical scanning electron microscopy has been used to determine the major element compositions of some natural and artificial silicate glasses and their microcrystalline equivalents derived by the frictional melting of intermediate to acid protoliths the data show that the matrices of the friction melts which cool to form pseudotachylytes are relatively basic and hydrous even when their protoliths are intermediate to acid this is because frictional fusion involves the selective comminution and nonequilibrium melting of minerals based on their individual mechanical properties and melting points not the formation of minimum melts through equilibrium mineral interaction this means that hydrous ferromagnesian minerals e g micas and amphiboles melt preferentially to form the liquid matrix while feldspars and especially quartz more readily survive as clasts pseudotachylytes generated by frictional melting are therefore not bulk melts and as clast melt suspensions they cannot be considered as simple newtonian fluids the calculated viscosities of the friction melts are low for example at 1200 c most friction melts possess zero shear suspension viscosities of 102 104 dpa s 1 dpa s 1 p this is equivalent to the viscosities of tholeiitic and alkaline basaltic magmas at the same temperature these viscosities are maximum determinations because as clast melt suspensions friction melts may undergo shear thinning and exhibit pseudoplasticity at high shear rates i e during slip on a fault surface contrary to earlier suggestions where the bulk melting of intermediate to acid protoliths was believed to result in the generation of viscous friction melts that could act to inhibit continued sliding this work shows that most pseudotachylytes are partial melts possessing low viscosities the formation of highly fluid suspensions during slip may have profound effects on the dissipation of stored strain energy in the rocks surrounding a fault interface lubrication could facilitate an increase in the slip rate and the rate of energy dissipation this would be manifest as an increase in high frequency seismic wave radiation and vibrational

constructing constitutive relationships for seismic and aseismic fault slip for the purpose of modeling natural fault slip a useful result from an experimental fault mechanics study would be a physically based constitutive relation that well characterizes all the relevant observations this report describes an approach for constructing such equations where possible the construction intends to identify or at least attribute physical processes and contact scale physics to the observations such that the resulting relations can be extrapolated in conditions and scale between the laboratory and the earth the approach is developed as an alternative but is based on ruina 1983 and is illustrated initially by constructing a couple of relations from that study in addition two example constitutive relationships are constructed these describe laboratory observations not well modeled by ruina s equations the unexpected shear induced weakening of silica rich rocks at high slip speed goldsby and tullis 2002 and fault strength in the brittle ductile transition zone shimamoto 1986 the examples provided as illustration may also be useful for quantitative modeling

frictional melting of gabbro under extreme experimental conditions of normal stress acceleration and sliding velocity 1 with the advent of high velocity shear apparatus several experimental studies have been performed in recent years improving our understanding of the evolution of fault strength during seismic slip however these experiments were conducted under relatively low normal stress 20 mpa and using small cylindrical samples where a large gradient in slip velocity exists across the sliding surface given the above limitations the extrapolation of these experimental results to natural conditions is not trivial here we present results from an experimental study on gabbroic rocks using a newly developed rotary shear apparatus capable of reaching higher normal stress up to 50 mpa on ring shaped samples 30 50 mm internal external diameter and allowing precise control of the imposed slip velocity function the results confirm that steady state shear stress during the melt lubricated phase of the experiment depends on normal stress in the form of a power law equation as predicted by theoretical models however the exponent appears closer to 0 5 contrary to the theoretical prediction of 0 25 we observe no systematic dependence of shear stress on acceleration but increasing deceleration drastically decreases the recovery of friction during final slip we find that the slip weakening distance decreases inversely with increasing normal stress in agreement with theoretical considerations and decreases with increasing slip rate extrapolation of the slip weakening distance to natural conditions predicts a slip velocity for ancient seismic events of 0 3 1 m s when compared with field estimates these values compare well with seismological estimates

fractal dimension of molten surfaces as a possible parameter to infer the slip weakening distance of faults from natural pseudotachylytes high velocity friction experiments on gabbro and monzodiorite using a rotary shear high velocity friction apparatus have revealed that frictional melting and progressive growth of a molten layer along a fault cause slip weakening eventually reaching a nearly steady state the melting surface at the host rock molten layer interface is initially very flat but it becomes more complex and rounded in shape towards the steady state owing to the selective melting of minerals with lower melting points and the gibbs thomson effect this change in the melting surface topography can be quantitatively expressed by the fractal dimension d as determined by the divider method from about 1 0 near the peak friction to around 1 1 near the steady state friction the ultimate fractal dimension at steady state friction tends to decrease with increasing heat production rate presumably due to more rapid and uniform melting a systematic correlation of d with mechanical behavior of the fault during frictional melting may provide a way of estimating slip weakening distance and heat production rate at steady state friction by measuring d for natural pseudotachylytes on slip surfaces with different displacements the weakening distance is of vital significance in relation to fault instability and the heat production rate is related to the fault strength the experimental studies point to ways to estimate these difficult quantities for natural faults

the mechanics of lubricated faults insights from 3 d numerical models 1 the weakening mechanisms occurring during an earthquake failure are of prominent importance in determining the resulting energy release and the seismic waves excitation in this paper we consider the fully dynamic response of a seismogenic structure where lubrication processes take place in particular we numerically model the spontaneous propagation of a 3 d rupture in a fault zone where the frictional resistance is controlled by the properties of a low viscosity slurry formed by gouge particles and fluids this model allows for the description of the fault motion in the extreme case of vanishing effective normal stress by considering a viscous fault response and therefore without the need to invoke in the framework of coulomb friction the generation of the tensile mode of fracture we explore the effects of the parameters controlling the resulting governing law for such a lubricated fault the viscosity of the slurry the roughness of the fault surfaces and the thickness of the slurry film our results indicate that lubricated faults produce a nearly complete stress drop i e a very low residual friction coefficient 0 01 a high fracture energy density eg few 10s of mj m2 and significant slip velocities vpeak few 10s of m s the resulting values of the equivalent characteristic slip weakening distance d0eq 0 1 0 8 m depending on the adopted parameters are compatible with the seismological inferences moreover in the framework of our model we found that supershear ruptures are highly favored in the case of enlarging gap height we can have the healing of slip or even the inhibition of the rupture quantitative comparisons with different weakening mechanisms previously proposed in the literature such as the exponential weakening and the frictional melting are also discussed

the landslide stage of the hsiaolin catastrophe simulation and validation 1 typhoon morakot struck southern taiwan in the summer of 2009 causing the most severe flooding since the 1950s in the early morning of august 9 rainfall triggered the hsiaolin landslide and the resulting debris avalanche covered the township of hsiaolin village kaohsiung around five hundred people were buried alive reconstruction of the runout of the debris avalanche would increase understanding of the large scale avalanches for future hazard mitigation purposes simulation of the debris avalanche runout can provide valuable information for this purpose a new continuum shallow water model is applied to flow over general topography the coulomb friction law is adopted the friction coefficient is initially determined by high pressure rotary shearing tests and subsequently fine tuned by an iterative procedure to minimize the difference between the simulation and the measurement the friction coefficients measured by laboratory tests are found to be in reasonable agreement with the best fit result of the simulation in addition voellmy rheology is applied but it is found that the role of the fluid viscous drag is insignificant the simulation result in the village area is further corroborated by near surface magnetic surveys these indicate that the northern part of the village is dislocated while the artifact structures of the southern part are buried near their original locations by comparing the landslide front and the flow direction of the simulation we are able to confirm as also described by survivors that the landslide swept the northern part of the village into the cishan river while the southern part was flooded subsequently by the debris from a dam breach about 20 min after the landslide

rapid acceleration leads to rapid weakening in earthquake like laboratory experiments after nucleation a large earthquake propagates as an expanding rupture front along a fault this front activates countless fault patches that slip by consuming energy stored in earth s crust we simulated the slip of a fault patch by rapidly loading an experimental fault with energy stored in a spinning flywheel the spontaneous evolution of strength acceleration and velocity indicates that our experiments are proxies of fault patch behavior during earthquakes of moment magnitude mw 4 to 8 we show that seismically determined earthquake parameters e g displacement velocity magnitude or fracture energy can be used to estimate the intensity of the energy release during an earthquake our experiments further indicate that high acceleration imposed by the earthquake s rupture front quickens dynamic weakening by intense wear of the fault zone

the effect of water on strain localization in calcite fault gouge sheared at seismic slip rates abstract strain localization during coseismic slip in fault gouges is a critical mechanical process that has implications for understanding frictional heating the earthquake energy budget and the evolution of fault rock microstructure to assess the nature of strain localization during shearing of calcite fault gouges high velocity v max 1 m s rotary shear experiments at normal stresses of 3 20 mpa were conducted under room dry and wet conditions on synthetic calcite gouges containing dolomite gouge strain markers when sheared at 1 m s the room dry gouges showed a prolonged strengthening phase prior to dynamic weakening whereas the wet gouges weakened nearly instantaneously microstructural analysis revealed that a thin

strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates 1 high velocity friction tests were conducted on solid and hollow cylinders of carrara calcite marble dolomite marble silicate bearing calcite marble and calcite gouge to investigate the strength of carbonate faults during seismic slip the experiments performed at normal stresses of 0 6 14 7 mpa slip rates of 0 03 1 60 m s and room temperature in a rotary shear friction testing machine yielded an extraordinarily low steady state friction coefficient 0 1 at slip rates of 1 1 1 2 m s the slip weakening distance of 4 28 m became shorter at higher normal stress or frictional work rate strong velocity weakening was observed not only in steady state but also in nonsteady state friction while the slip rate was changing thus slip deceleration was accompanied by fault strength recovery large rapid temperature rises in narrow shear localization zones less than a few micrometers induced carbonate decomposition such as the breakdown of calcite into aggregates of cao nanograins and co2 in carrara marble scanning electron microscope observation revealed that the shear localization zone in the highly porous decomposition product was a layer of scattered small grains mostly 1 m in diameter these microstructures and the measured high permeability 10 14 m2 of the decomposed marble indicate that the dominant weakening mechanism in our experiments was possibly powder lubrication powder rheology at high slip rates is not yet well understood but the frictional behavior of nanograins appears to be strongly velocity dependent if decarbonation occurs during seismic slip in natural carbonate faults powder lubrication may make the faults slippery even under fluid drained conditions

frictional melting processes and products in geological materials introduction and discussion this special issue is the outcome of a theme session convened by the above authors entitled frictional melting processes and products in geologic materials held at the 1990 geological society of america annual meeting in dallas texas u s a the goals of the session were threefold to bring together researchers working on various aspects of frictional melting in rock to provide a forum for the exchange of new ideas and to encourage the production of a thematic set of papers dedicated to the topic of the eight papers presented here the first two spray swanson are primarily processand mechanism oriented the next magloughlin maddock o hara deal primarily with chemical aspects of host rock pseudotachylyte relations the last three mainly provide descriptions of naturally occurring koch and masch techmer et al and artificially produced kennedy and spray friction melts natural pseudotachylytes are described from strike slip zones magloughlin swanson thrusts and their listric counterparts koch and masch techmer et al and connecting lateral ramps o hara thus it appears that there exists an association between pseudotachylyte generation and relatively long lived largedisplacement faulting and shearing the prime objective of the meeting was to promote the integration of different approaches

a pseudotachylyte geothermometer abstract pseudotachylytes invariably contain a conspicuous concentration of clasts and lithic fragments in their matrices which reflect brittle wear processes during frictional melting the ratio of clasts to matrix is interpreted as the ratio of wear to melt w m and measurements of this ratio show a range of 0 1 0 7 based on models of melting and wear processes it is shown that the ratio w m is independent of fault displacement stress fault area and mineralogy thermodynamic considerations indicate that w m corresponds to the thermodynamic efficiency of the conversion of work to heat and is defined as w q thigh tlow thigh where thigh refers to the melt temperature and tlow is the ambient country rock temperature this provides a simple new technique for estimating the ambient crustal temperature tcrust in degrees kelvin t crust 1 w m t melt assuming a reasonable value for the temperature of the melt estimates of country rock temperatures tcrust for pseudotachylytes from four different localities in the usa indicate a range of 123 387 c eclogite facies pseudotachylytes from western norway yield a mean country rock temperature of 658 c in good agreement with independent fe mg exchange geothermometry this new geothermometer appears to be applicable throughout the entire crust and may provide a better understanding of melting and wear processes during seismic faulting

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

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

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

rupture to the trench frictional properties and fracture energy of incoming sediments at the cascadia subduction zone abstract the mechanical properties of sediment inputs to subduction zones are important for understanding rupture propagation through the accretionary prism during megathrust earthquakes clay minerals strongly influence the frictional behavior of fault gouges and the clay content of subduction input materials varies through a stratigraphic section as well as for subduction margins globally to establish the frictional properties of the shallow cascadia subduction zone and place the results in a global context we conducted high velocity rotary shear experiments on odp core samples retrieved from cascadia input sediments 35 45 clay and a suite of individual clay species we compared our results to a compilation of published high velocity experiments conducted on samples of wet gouge dry gouge and intact rock for each sample type three trends were identified with increasing normal stress 1 the stress drop p s s increases linearly 2 the characteristic thermal weakening distance d t h decreases as a power law function except for wet clay rich gouges and 3 the fracture energy w b shows no dependence however fracture energy does vary with sample type clay rich gouges under wet conditions have the lowest fracture energy and fracture energy for both dry and wet gouges is at least an order of magnitude lower than estimates from intact rocks therefore when clay rich lithologies are present they may minimize spatial variations in frictional behavior allowing earthquakes to propagate to the trench for cascadia input sediments there is little variation in the fracture energy between lithologies but the fracture energy of cascadia sediments is around an order of magnitude higher than input sediments from other subduction margins the high fracture energy of cascadia sediments relative to other subduction margins may inhibit large amounts of shallow earthquake slip and dynamic overshoot

friction evolution of granitic faults heating controlled transition from powder lubrication to frictional melt the experimental shearing of granitic faults revealed complex evolution of strength and microstructure we use a rotary shear apparatus to shear three types of granitic rocks at moderate slip velocity of 0 01 0 11 m s normal stress of 1 0 6 8 mpa and slip distance up to 60 m three stages of strength evolution with slip distance were systematically observed in stage i faults exhibited initial weakening in which the friction coefficient dropped to a steady state level of 0 3 this weakening is associated with powder lubrication and the development of cohesive gouge layers stage ii included strengthening to 0 5 associated with volumetric expansion melting of fault patches and viscous braking at these patches in stage iii fault weakening is due to melt lubrication when the melted patches reach a critical fraction of the fault surface area we show that this complex weakening strengthening weakening evolution is controlled by thermally activated deformation processes that can explain the friction behavior of igneous rocks at seismic velocity range

permeability structure and co seismic thermal pressurization on fault branches insights from the usukidani fault japan detailed mapping of complex fault zones shows that secondary faults often branch off the principal slip zone however the effect of secondary branch faults on the hydrodynamic beha viour of fault zones has not yet been examined largely because of a lack of hydraulic data and because numerical or analogue modelling of splay faulting is a complex issue this contribution investigates the thermal pressurization process in cases of slip along a principal slip zone and along splay faults branching off the principal displacement zone the study is based on porosity and permeability data presented in this paper from the principal and secondary slip zones of an active clay rich gouge bearing strike slip fault the usukidani fault of sw japan modelling con strained by these data suggests that thermal pressurization is a viable process only as long as the rupture remains located in the central gouge zones or in mature splay fault gouge zones splaying of the rupture into surrounding microbreccias or into immature or newly generated splay faults of higher permeability will release fluid pressure or inhibit the generation of coseismic excess fluid pressures by thermal pressurization the modelling results suggest that secondary fault branches can play a key role in controlling fluid pressurization during faulting hence complete investi gation of active fault zones needs to include secondary faults and their corresponding hydraulic behaviour in order to establish the influence of such structures on earthquake mechanics

wear processes in rocks at slow to high slip rates abstract frictional wear experiments are performed on diorite granite and sandstone at sliding velocities of 0 004 0 27 m s under normal stresses of 0 21 6 3 mpa using a rotary shear apparatus to establish velocity dependent wear laws of rocks and to determine the partition of frictional work used for gouge generation power laws between normal shear stresses and steady state wear rate defined as thickness of gouge formed fault displacement account for our data for diorite and granite at low velocities and most experimental data on wear of rocks reported in the literature but an exponential law holds for wear of diorite at velocities greater than 0 11 m s and its wear rate increases dramatically at seismic slip rates a change from the power law to the exponential law seems to be caused by frictional heating and thermal fracturing both power and exponential laws can describe data for granite sandstones exhibit complex wear behavior possibly due to development of shiny slickenside surface that suppresses wear our data for diorite indicate that at the investigated normal stresses only 0 004 of frictional work is consumed for gouge formation at velocities less than 0 11 m s but this fraction increases markedly with increasing velocity energy partition for gouge formation is not constant and changes with velocity during earthquakes

transient water adsorption on newly formed fault gouge and its relation to frictional heating determination of the amount of frictional heating on faults during slips provides insight into the mechanics of faulting fault slips cause frictional heating as well as production of gouge materials newly formed gouge is mechanochemically stimulated to gain a transient water adsorption ability we showed that the synthetic gouge from friction tests on rocks at a 1 mm s slip rate without frictional heating adsorbed a large amount of water comparable to that adsorbed by clay minerals the amount of adsorbed water decreased significantly with increasing slip rate to 100 mm s where the fault temperature increased above 400 c we confirmed there was no additional adsorption on the heated gouges after termination of the slip we conclude that the adsorption state can be considered a new indicator of a temperature rise of 400 c by frictional heating associated with recent near surface faulting

stress breakdown time and slip weakening distance inferred from slip velocity functions on earthquake faults we estimate the critical slip weakening distance on earthquake faults by using a new approach which is independent of the estimate of fracture energy or radiated seismic energy the approach is to find a physically based relation between the breakdown time of shear stress tb the time of peak slip velocity tpv and the slip weakening distance dc from the time histories of shear stress slip and slip velocity at each point on the fault which can be obtained from dynamic rupture calculations using a simple slip weakening friction law numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3d half space and a more realistic horizontally layered structure with finite difference schemes the results show that tpv is well correlated with tb for faults even with a heterogeneous stress drop dis tribution except at locations near strong barriers and the fault edges we also inves tigate this relation for different types of slip weakening behavior we have applied the method to two recent strike slip earthquakes in western japan the 2000 tottori and the 1995 kobe events we integrated the slip velocity functions on the vertical fault obtained from kinematic waveform inversion of strong motion and teleseismic records from the arrival time of rupture tr to the time of the peak slip velocity tpv and we then corrected the slip obtained at tpv for the errors expected from the dynamic calculations it was found that the slip weakening dis tance d c estimated in the frequency window between 0 05 and 0 5 hz ranges between 40 and 90 cm on the two earthquake faults however if we consider the limited frequency resolution of the observed waveforms probable time errors in the slip velocity functions obtained from kinematic inversion and the uncertainty of the slip weakening behavior the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values the estimated dc values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip this possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers in addition to stress heterogeneities

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

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

frictional strength of fault gouge in taiwan chelungpu fault obtained from tcdp hole b abstract three fault zones fzb1136 fzb1194 and fzb1243 are found in core samples in hole b borehole penetrating through the chelungpu fault central taiwan that activated at the 1999 taiwan chi chi earthquake each fault zone is composed of a black gouge zone bgz and a gray gouge zone ggz surrounded by a fault breccia zone bz and or fracture damaged zone fz we conducted tri axial friction experiments on samples collected from subzones of the above three fault zones under the 1 km depth ambient condition with axial shortening rates of 0 1 to 10 m s to investigate frictional strength and its velocity dependence we found that the coefficient of friction is 0 3 for the bgz at fzb1136 1136bgz which is lower than those at other fault zones this result indicates that fault slip at the chi chi earthquake occurred at the 1136bgz the estimated frictional strength profile across fzb1136 was that the frictional strength was the lowest the coefficient of friction was 0 3 for the bgz and increased up to 0 5 for undeformed host rock with increasing distance from the bgz presence of the intermediate frictional strength zone consisting of the ggz and the bz suggests a development of off fault damage zone where deformation occurred not only in the bgz but also in the intermediate zone this feature should be important to estimate total fracture energy released during earthquakes we also suggest that coefficients of friction and the velocity dependences of the samples are closely related to localization of shear deformation and clay content respectively

importance of thermochemical pressurization in the dynamic weakening of the longmenshan fault during the 2008 wenchuan earthquake inferences from experiments and modeling 1 we determined the internal structure and mineral composition of the yingxiu beichuan fault zone at the zhaojiagou exposure and measured frictional and transport properties of the fault rocks collected to gain a better understanding of dynamic weakening mechanisms during seismic fault motion this fault is a major fault in the longmenshan fault system that caused the 2008 wenchuan earthquake the exposure studied is located midway along the surface rupture close to where the largest coseismic displacement occurred high velocity friction experiments reveal exponential slip weakening from a peak friction toward a steady state value slip weakening is more pronounced for water dampened gouge than dry gouge suggesting thermal pressurization the fault gouge has a very low permeability 10 21 m2 at 165 mpa effective pressure and is surrounded by fault breccia with a permeability of 10 19 to 10 17 m2 grading into less permeable fractured country rocks the fault zone thus exhibits a conduit barrier structure allowing fluid flow only in the breccia zone we numerically modeled coseismic slip weakening including thermal pressurization and mineral dehydration decarbonation basing our calculation on measured frictional and transport properties and on the slip history inferred for the wenchuan earthquake the results indicate that 1 thermochemical pressurization played an important role in causing dynamic slip weakening 2 the slip weakening distance is similar to the seismologically determined values and 3 pore pressures might have exceeded the normal stress thus maintaining temperatures below 600 c interestingly enough heat was generated to fully remove and thermally pressurize the interlayer water from smectite contributing an excess pore pressure of 6 mpa in addition we found that the incorporation of state dependent fluid properties predicts much more efficient fluid pressurization than using constant properties the dramatic weakening predicted probably offers a compelling explanation for the large coseismic displacement and slip acceleration observed near beichuan city

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

rheology of bubble bearing magmas abstract the physical effects of air or argon bubbles on the rheology of a calcium aluminosilicate melt have been measured at temperatures ranging from 830 to 960 c at 1 bar pressure the melt composition is sio 2 64 al 2 o 3 23 and cao 13 wt while bubble volume fractions are 0 0 06 0 13 0 32 0 41 and 0 47 measured newtonian viscosities range from 10 10 to 10 14 dpa s melts with bubble fractions of 0 06 and 0 13 show with increasing temperature t an increasing relative viscosity for t t 850 c for all bubble fractions the viscosity decreases markedly with temperature the observed maximum decrease of the relative viscosity is 75 for a bubble fraction of 0 47 at 907 c at all bubble fractions the viscosity is independent of the applied stress which ranged from 11 to 677 bars no clear indications were observed of non newtonian rheological behavior under our experimental conditions the relative viscosity of the two phase liquid depends primarily on the bubble fraction physical and volcanological implications of these measurements are discussed

petrological architecture of a magmatic shear zone a multidisciplinary investigation of strain localisation during magma ascent at unzen volcano japan shearing of magma during ascent can promote strain localisation near the conduit margins anymechanical and thermal discontinuities associated with such events may alter the chemical physicaland rheological stability of the magma and thus its propensity to erupt lava spines can record suchprocesses preserving a range of macroscopic and microscopic deformation textures attributed toshearing and friction as magma ascends through the viscous brittle transition here we use a multi disciplinary approach combining petrology microstructures crystallography magnetics and experi mentation to assess the evidence role and extent of shearing across a marginal shear zone of the1994 1995 lava spine at unzen volcano japan our results show that crystals can effectively moni tor stress conditions during magma ascent with viscous remobilisation crystal plasticity and com minution all systematically increasing towards the spine margin accompanying this we find anincrease in mineral destabilisation in the form of pargasitic amphibole breakdown displaying tex tural variations across the shear zone from symplectitic to granular rims towards the spine margin in addition the compaction of pores chemical and textural alteration of interstitial glass and mag netic variations all change systematically with shear intensity the strong correlation between thedegree of shearing crystal deformation and disequilibrium features together with distinct magneticproperties implies a localised thermal input due to shear and frictional processes near the conduitmargin during magma ascent this was accompanied by late stage or post emplacement fluid andgas induced alteration of the gouge as well as oxidation and glass devitrification understandingand recognising evidence for strain localisation during magma ascent may therefore be vital whenassessing factors that regulate the style of volcanic eruptions which may provide insights into thecryptic shifts from effusive to explosive activity as observed at many active lava domes

low to high velocity frictional properties of the clay rich gouges from the slipping zone of the 1963 vaiont slide northern italy the final slip of about 450 m at about 30 m s of the 1963 vaiont landslide italy was preceded by 3 year long creeping phase which was localized in centimeter thick clay rich layers 60 70 smectites 20 30 calcite and quartz here we investigate the frictional properties of the clay rich layers under similar deformation conditions as during the landslide 1 5 mpa normal stress 2 10 7 to 1 31 m s slip rate and displacements up to 34 m experiments were performed at room humidity and wet conditions with biaxial torsion and rotary shear apparatus the clay rich gouge was velocity independent to velocity weakening in both room humidity and wet conditions in room humidity experiments the coefficient of friction decreased from 0 47 at v 0 70 m s full lubrication results from the formation of a continuous water film in the gouge the vaiont landslide occurred under wet to saturated conditions the unstable behavior of the landslide is explained by the velocity weakening behavior of the vaiont clay rich gouges the formation of a continuous film of liquid water in the slipping zone reduced the coefficient of friction to almost zero even without invoking the activation of thermal pressurization this explains the extraordinary high velocity achieved by the slide during the final collapse

frictional evolution acoustic emissions activity and off fault damage in simulated faults sheared at seismic slip rates we present a series of high velocity friction tests conducted on westerly granite using the slow to high velocity apparatus shiva installed at istituto nazionale di geofisica e vulcanologia roma with acoustic emissions aes monitored at high frequency 4 mhz both atmospheric humidity and pore fluid water pressure conditions were tested under effective normal stress sigma eff n in the range 5 20 mpa and at target sliding velocities v s in the range 0 003 3 m s under atmospheric humidity two consecutive friction drops were observed the first one is related to flash weakening and the second one to the formation and growth of a continuous layer of melt in the slip zone in the presence of fluid a single drop in friction was observed average values of fracture energy are independent of effective normal stress and sliding velocity however measurements of elastic wave velocities on the sheared samples suggested that larger damage was induced for 0 1 v s 0 3 m s this observation is supported by aes recorded during the test most of which were detected after the initiation of the second friction drop once the fault surface temperature was high some aes were detected up to a few seconds after the end of the experiments indicating thermal rather than mechanical cracking in addition the presence of pore water delayed the onset of aes by cooling effects and by reducing of the heat produced supporting the link between aes and the production and diffusion of heat during sliding using a thermoelastic crack model developed by fredrich and wong 1986 we confirm that damage may be induced by heat diffusion indeed our theoretical results predict accurately the amount of shortening and shortening rate supporting the idea that gouge production and gouge comminution are in fact largely controlled by thermal cracking finally we discuss the contribution of thermal cracking in the seismic energy balance in fact while a dichotomy exists in the literature regarding the partitioning between fracture and heat energy the experimental evidence reported here suggests that both contribute to fault weakening and off fault damage

shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes as a result of the comminution that takes place over numerous earthquake cycles mature faults are characterized by thick layers of pulverized gouge with finite porosity that is saturated with water at seismogenic depths the heat generated during earthquakes raises the gouge temperature and thermal expansion of the pore fluid and surrounding solids produce elevated pore pressures that cause fault strength to decrease in the process known as thermal pressurization building upon this framework we describe a model that imposes a plane strain configuration and shows that the stress variations caused by porothermoelasticity promote the mohr coulomb failure of previously undeformed regions except in special cases where the friction is rate strengthening we find that the frictional strength must vary throughout the post failure region which we identify in our model with the shear zone we introduce a strain rate function that describes the overall influence of distributed slip on energy dissipation and fault strength as the shear zone thickness expands using typical fault parameters at 7 km depth the shear zone reaches several millimeters of thickness after 1 s sliding at an overall rate of 1 m s the expansion of the shear zone limits the temperature rise to several hundred degrees celsius and the average fault strength falls to about a tenth of the static frictional strength

coseismic thermal pressurization can notably prolong earthquake recurrence intervals on weak rate and state friction faults numerical experiments using different constitutive equations 1 we add a new perspective to component factors of earthquake cyclicity namely coseismic thermal pressurization tp within fluid saturated fault zones which is pore fluid pressurization caused by frictional heating by using a single degree of freedom system with a rate and state dependent friction law we show that the short lived tp can prolong earthquake recurrence intervals this lengthening effect can operate even without any notable shear heating in weak faults moreover if the maximum increase in temperature is above a certain level the permeability rather than the maximum temperature becomes important for the lengthening effect lower permeability causes longer recurrence intervals by contrast narrower slip zones more pronounced heating do not simply prolong recurrence intervals although they entail higher dynamic undershoot and energy radiation these features do not depend on whether the assumed evolution law is the ruina law or the dieterich law however our results indicate that if the degree of tp changes for each earthquake the ideal time predictable model for earthquake cycles can be applicable only in the case of faults obeying the ruina law furthermore on the basis of the above mentioned dependence of the interval on the permeability we point out that it is necessary to measure the permeability rather than the slip zone thickness or the increase in temperature in order to estimate the tp effect on long term earthquake cycles although it is currently difficult to measure the permeability under ground measurements should be performed in the light of the importance of permeability in the prediction of future seismic hazards

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

geologic evidence for multiple slip weakening mechanisms during seismic slip in crystalline rock we examine exhumed seismogenic faults to investigate the mechanisms that may have achieved dynamic fault weakening during ancient ruptures field and microscope observations imply more than one weakening mechanism must have been active during slip events on the faults pseudotachylytes that are continuous over the scale of field exposures are indicative of melt lubrication a fault breccia crosscutting earlier formed cataclasites was mobilized during faulting and possibly represents a pressurized fault rock that resulted from thermal pressurization or elastohydrodynamic lubrication in some faults pseudotachylytes are developed in patches several meters long cataclasites in which there is no evidence for melting are present immediately along strike from the pseudotachylyte patches by considering the energy required for melting we show that the pseudotachylytes must have formed during ruptures larger than the patches implying that the cataclasites also accommodated seismic slip the distribution of fault rock types shows that the frictional response to slip during a single event was spatially variable reworked pseudotachylytes also indicate that coseismic processes change over time at a point on a fault these observations emphasize that macroscopic dynamic fault weakening is a function of multiple coeval processes at microscales to mesoscales detailed observations of the discontinuous pseudotachylytes show that slip zone thickness is the critical parameter that controls active coseismic processes the frictional response of a fault to slip is therefore dependent on the internal structure of faults given the along strike heterogeneity of most mapped fault zones the coexistence of multiple slip weakening mechanisms in a single earthquake will be common

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

thermochemical pressurization of faults during coseismic slip 1 during earthquakes frictional heating on the fault plane induces a temperature rise and thus a pore pressure rise which is known as thermal pressurization tp coseismic mineral dehydrations may occur because of this temperature increase and are included within the tp framework dehydrations are modeled as a source term for pore pressure because of the total volume change and as a sink term for temperature because they are endothermic the reaction occurs within the slipping zone when a threshold temperature ts is reached dehydration reaction kinetic is modeled using a first order reaction rate using energy and fluid mass conservation we derive analytically the equations of evolution of pore pressure temperature and reaction extent in the undrained adiabatic case using a constant reaction rate we investigate the values of the kinetic rate constant required to produce a significant effect which are much higher than laboratory data reported in the literature on clay serpentine and phyllosilicate dehydration we show however that such high values can be reached if the temperature dependency of the rate constant is taken into account next we include fluid and heat transport and use an arrhenius law to calculate the rate constant as a function of temperature the subsequent set of differential equations is then solved numerically the main effect of dehydration reactions is an increase of pore pressure and a stabilization of the temperature during slip we explore a wide range of parameters in order to determine in which cases dehydration can be considered as a nonnegligible process for high permeability rocks 10 18 m2 and when the amount of water that can be released is of the order of 10 dehydration is an important mechanism as it delays the onset of melting which would normally occur even within the tp framework if the onset temperature is low compared to the initial temperature t0 ts t0 150 c overpressure can occur if the reactions are highly endothermic and if their kinetic is fast enough frictional melting would not occur unless the dehydration reactions are completed within the slipping zone

frictional melting of peridotite and seismic slip 1 the evolution of the frictional strength along a fault at seismic slip rates about 1 m s is a key factor controlling earthquake mechanics at mantle depths friction induced melting and melt lubrication may influence earthquake slip and seismological data we report on laboratory experiments designed to investigate dynamic fault strength and frictional melting processes in mantle rocks we performed 20 experiments with balmuccia peridotite in a high velocity rotary shear apparatus and cylindrical samples 21 8 mm in diameter over a wide range of normal stresses 5 4 16 1 mpa slip rates 0 23 1 14 m s and displacements 1 5 71 m during the experiments shear stress evolved with cumulative displacement in five main stages stages 1 5 in stage 1 first strengthening the coefficient of friction increased up to 0 4 0 7 first peak in friction in stage 2 abrupt first weakening decreased to about 0 25 0 40 in stage 3 gradual second strengthening shear stress increased toward a second peak in friction 0 30 0 40 in stage 4 gradual second weakening the shear stress decreased toward a steady state value stage 5 with 0 15 stages 1 and 2 are of too short duration to be investigated in detail with the current experimental configuration by interrupting the experiments during stages 3 4 and 5 microstructural field emission scanning electron microscope and geochemical electron probe micro analyzer and energy dispersive x ray spectroscopy analysis of the slipping zone suggest that second strengthening stage 3 is associated with the production of a grain supported melt poor layer while second weakening stage 4 and steady state stage 5 are associated with the formation of a continuous melt rich layer with an estimated temperature up to 1780 c microstructures formed during the experiments were very similar to those found in natural ultramafic pseudotachylytes by performing experiments at different normal stresses and slip rates 1 the thermal as it includes the thermally activated first and second weakening slip distance to achieve steady state from the first peak in strength decreased with increasing normal stress and slip rate and 2 the steady state shear stress slightly increased with increasing normal stress and for a given normal stress decreased with increasing slip rate the ratio of shear stress versus normal stress was about 0 15 well below the typical friction coefficient of rocks 0 6 0 8 the dependence of steady state shear stress with normal stress was described by means of a constitutive equation for melt lubrication the presence of microstructures similar to those found in natural pseudotachylytes and the determination of a constitutive equation that describes the experimental data allows extrapolation of the experimental observations to natural conditions and to the study of rupture dynamics in mantle rocks