large scale pseudotachylytes and fluidized cataclasites from an ancient subduction thrust fault in the kodiak accretionary complex kodiak island alaska pseudotachylyte occurs in black locally vitreous ultrafine grained fault rock microscopic observations show that the pseudotachylytes are composed of glass with vesicles amygdules microlites and flow structures indicating a frictional melt the pseudotachylyte is gradational to cataclasite and shows outcrop scale injection and ductile deformation structures the cataclasite was ductily mobile i e fluidized simultaneous with the formation and emplacement of pseudotachylyte melt the pseudotachylytic rocks postdate the stratal disruption fabric of associated shear zone melanges and show similar direction of thrust transport and have undergone limited subsequent deformation we interpret the stratal disruption as resulting from underthrusting of the subducting plate and pseudotachylyte development as the final activity of this thrust surface the gradational contacts between pseudotachylyte and cataclasite demonstrate that the cataclasite also formed as a seismic product and may represent paleoseismic rupture zones possibly of very great earthquakes with or without accompanying pseudotachylytes the pseudotachylytes are voluminous and many are spatially disconnected from generation surfaces this style is distinct from pseudotachylytes described in other environments and this may explain the rarity of documented examples of subduction thrust pseudotachylyte

rethinking conditions necessary for pseudotachylyte formation observations from the otago schists south island new zealand abstract pseudotachylytes and two distinct types of cataclasite in the otago schist at tucker hill south island new zealand provide evidence for both seismic slip and aseismic creep on a normal fault zone during regional crustal extension in late cretaceous time regional geologic evidence suggests that the fault had its present low angle dip ca 10 at the time it was active type a cataclasites presumably aseismic can be recognized by bi fractal grain size distributions monomict composition angular clasts of uniform textural maturity and a crude fabric defined by oriented grains and transgranular fractures type b cataclasites possibly cosesimic have characteristics consistent with fluidized grain flow including heterogeneous clast shapes and types a bimodal grain size distribution intrusive relationships with other rocks and the absence of any fabric or transecting fractures pseudotachylyte which occurs as fault veins injection veins and more complex types of intrusive structures consistently cuts across and invades type a cataclasites but is both intrusive into and included as clasts in type b cataclasites these relationships are consistent with a fault evolution model in which the development of a damage zone through aseismic cataclasis type a facilitates the formation of pseudotachylyte in a subsequent seismic event by providing a permeable matrix through which fluids can drain in the early stages of slip thereby maintaining frictional contact between rock surfaces the formation of pseudotachylyte in turn may seal the fault zone and lead to thermal pressurization in a later seismic cycle forming fluidized type b cataclasites seismic slip on the low angle normal fault zone at tucker hill may have occurred by two distinct modes of dynamic weakening melt lubrication and thermal pressurization in successive seismic events although there is a perception among geologists that pseudotachylyte is most likely to form in intact crystalline rocks geophysical models of fault zones clearly demonstrate that pseudotachylyte formation is actually suppressed in low permeability rock because any fluids present would be unable to escape the fault zone and thermal pressurization would rapidly reduce frictional resistance the paradigmatic occurrences of pseudotachylyte in otherwise pristine crystalline rocks probably represent somewhat exceptional circumstances single rupture events at very high effective stress in dry rock coseismic frictional melts may actually be more common in hydrated rocks like the schist at tucker hill but harder to recognize and also vulnerable to overprinting as a fault zone matures in such rocks pseudotachylyte may represent an intermediate stage in the evolution of a fault zone the period between the formation of a high permeability damage zone and the development of a low permeability fault core

frictional melting processes in planetary materials from hypervelocity impact to earthquakes frictional melting is the result of the conversion of mechanical deformation to heat under adiabatic conditions of slip within planetary materials which are mainly natural ceramics frictional melting occurs at high strain rates typically 10 2 s 1 and at slip velocities greater than 0 1 m s 1 t he pathway to friction melting is controlled by the mechanical properties of a rock s constituent minerals especially fracture toughness minerals with the lowest fracture toughnesses and breakdown temperatures are preferentially comminuted and fused to form the melt the product is a polyphase suspension comprising mineral and rock fragments enclosed in a liquid matrix this cools to form the rock type known as pseudotachylyte and at even higher strain rates it forms shock veins in meteorites and in impact craters which may contain high pressure mineral polymorphs the generation of melt on sliding surfaces can lubricate earthquake faults facilitate the post shock modification of impact craters and make landslides more hazardous

the evolving energy budget of experimental faults within continental crust insights from in situ dynamic x ray microtomography abstract we investigate the evolving distribution of strain produced by a sliding fault within intact crystalline rock and the energetics of deformation that occur both on and off fault we slid precut faults of differing roughness oriented at 45 to 1 while acquiring in situ x ray microtomograms digital volume correlation of tomograms provide estimates of the 3d displacement and strain fields this characterization of the strain tensor field reveal that the differing fault roughness produced distinct slip behavior degree of strain localization and accumulation and energy budget partitioning the rougher fault slipped more episodically hosted a wider and more asymmetric damage zone and accommodated less normal and shear strain this fault consumed more energy in off fault deformation wint per volume and more energy in frictional slip wfric as portions of the total energy input to the system wext than the smoother fault in both experiments wfric consumed the largest portion of the energy budget 50 100 while wint consumed smaller percentages 5 20 tracking the temporal variability of energy partitioning revealed how evolving fault architecture determined the energetic dominance of particular deformational processes and so highlighted the importance of tracking energy partitioning through time

biomarkers heat up during earthquakes new evidence of seismic slip in the rock record during earthquakes faults heat up due to frictional work however evidence of heating from paleoearthquakes along exhumed faults remains scarce here we describe a method using thermal maturation of organic molecules in sedimentary rock to determine whether a fault has experienced differential heating compared to surrounding rocks we demonstrate the utility of this method on an ancient pseudotachylyte hosting megathrust at pasagshak point alaska measurements of the ratio of thermally stable to thermally unstable compounds diamondoids n alkanes show that the melt bearing rocks have higher thermal maturity than surrounding rocks furthermore the mineralogy of the survivor grains and the presence of any organic molecules allow us to constrain the temperature rise during the ancient earthquakes to 840 1170 c above ambient temperatures of 260 c from this temperature rise we estimate that the frictional work of the earthquake was 105 228 mj m 2 using experimental friction measurements as a constraint we estimate that the minimum slip necessary for heating was 1 8 m this paper demonstrates that biomarkers will be a useful tool to identify seismic slip along faults without frictional melt

coseismic fluid rock interactions at high temperatures in the chelungpu fault chemical and isotopic variations in crushed material along the chelungpu fault in taiwan are suggestive of interactions at high temperatures with coseismically generated aqueous fluids high fluid pressures along the fault zone during the magnitude 7 6 chi chi earthquake in 1999 could have reduced friction and fault strength aqueous fluids are thought to have an essential role in faulting and the dynamic propagation of earthquake rupture fluid overpressure can affect earthquake nucleation1 2 and in a process termed thermal pressurization pore fluid pressure produced by frictional heating can reduce the effective normal stress acting on the fault surface3 4 5 this may lead to a marked reduction in fault strength during slip however the coseismic presence of fluids within slip zones and the role of fluids in dynamic fault weakening is still a matter of debate here we present compositions of major and trace elements as well as isotope ratios of core samples representing relatively undamaged as well as very fine grained deformed material from three active zones of the chelungpu fault taiwan depth profiles across the most intensely sheared bands that range in thickness from 2 15 cm exhibit sharp compositional peaks of fluid mobile elements and of strontium isotopes we suggest that high temperature fluids 350 c derived from heating of sediment pore fluids during the earthquake interacted with material within the fault zone and mobilized the elements the coseismic presence of high temperature fluids under conditions of low hydraulic diffusivity6 within the fault zone is favourable for thermal pressurization this effect may have caused a dynamic decrease of friction along the chelungpu fault during the 1999 magnitude 7 6 chi chi earthquake

clast cortex aggregates in experimental and natural calcite bearing fault zones abstract we investigated the formation mechanisms of rounded clast cortex aggregates a composite grain found in the slipping zones of faults hosted in calcite and clay rich rocks the natural aggregates contain a central clast commonly made of host rock fragments or reworked cataclasite from the slipping zone the central clasts are surrounded by an outer cortex of calcite or clay grains a few m or less in size in laboratory experiments on calcite gouges using two rotary shear apparatus we investigated the dependence of clast cortex aggregate formation on the applied slip rate normal stress total displacement and ambient humidity clast cortex aggregates formed at all investigated slip rates 100 m s to 1 m s but only at relatively low normal stresses 5 mpa the aggregates were better developed with increasing displacement up to 5 m and did not form in experiments with water dampened gouges in the experiments aggregates formed in low strain regions within the gouge layers adjacent to the highest strain slip zones we propose that clast cortex aggregates in calcite bearing slip zones form in the shallow portions of faults during shearing in relatively dry conditions but our experiments suggest that they cannot be used as indicators of seismic slip formation involves clast rotation due to granular flow accompanied by accretion of fine matrix material possibly facilitated by electrostatic forces

vaporization of fault water during seismic slip laboratory and numerical studies as well as field observations indicate that phase transitions of pore water might be an important process in large earthquakes we present a model of the thermo hydro chemo mechanical processes including a two phase mixture model to incorporate the phase transitions of pore water occurring during fast slip i e a natural earthquake in order to investigate the effects of vaporization on the coseismic slip using parameters from typical natural faults our modeling shows that vaporization can indeed occur at the shallow depths of an earthquake irrespective of the wide variability of the parameters involved sliding velocity friction coefficient gouge permeability and porosity and shear induced dilatancy due to the fast kinetics water vaporization can cause a rapid slip weakening even when the hydrological conditions of the fault zone are not favorable for thermal pressurization e g when permeability is high at the same time the latent heat associated with the phase transition causes the temperature rise in the slip zone to be buffered our parametric analyses reveal that the amount of frictional work is the principal factor controlling the onset and activity of vaporization and that it can easily be achieved in earthquakes our study shows that coseismic pore fluid vaporization might have played important roles at shallow depths of large earthquakes by enhancing slip weakening and buffering the temperature rise the combined effects may provide an alternative explanation for the fact that low temperature anomalies were measured in the slip zones at shallow depths of large earthquakes

thermal alteration of pyrite to pyrrhotite during earthquakes new evidence of seismic slip in the rock record seismic slip zones convey important information on earthquake energy dissipation and rupture processes however geological records of earthquakes along exhumed faults remain scarce they can be traced with a variety of methods that establish the frictional heating of seismic slip although each has certain assets and disadvantages here we describe a mineral magnetic method to identify seismic slip along with its peak temperature through examination of magnetic mineral assemblages within a fault zone in deep sea sediments cored from the japan trench one of the seismically most active regions around japan during the integrated ocean drilling program expedition 343 the japan trench fast drilling project fault zone sediments and adjacent host sediments were analyzed mineral magnetically supplemented by scanning electron microscope observations with associated energy dispersive x ray spectroscopy analyses the presence of the magnetic mineral pyrrhotite appears to be restricted to three fault zones occurring at 697 720 and 801 m below sea floor in the frontal prism sediments while it is absent in the adjacent host sediments elevated temperatures and coseismic hot fluids as a consequence of frictional heating during earthquake rupture induced partial reaction of preexisting pyrite to pyrrhotite the presence of pyrrhotite in combination with pyrite to pyrrhotite reaction kinetics constrains the peak temperature to between 640 and 800 c the integrated mineral magnetic microscopic and kinetic approach adopted here is a useful tool to identify seismic slip along faults without frictional melt and establish the associated maximum temperature

seismic heating signatures in the japan trench subduction plate boundary fault zone evidence from a preliminary rock magnetic geothermometer frictional heating during earthquake rupture reveals important information on earthquake mechanisms and energy dissipation the amount of annealing varies widely and is as yet poorly constrained here we use magnetic susceptibility versus temperature measurements during cycling to increasingly elevated temperatures to constrain the maximum temperature a slip zone has experienced the case study comprises sheared clay cored from the japan trench subduction plate boundary fault zone decollement which accommodated the large slip of the 2011 mw 9 0 tohoku oki earthquake the decollement was cored during the integrated ocean drilling program iodp expedition 343 the japan trench fast drilling project jfast heating signatures with estimated maximum temperatures ranging from 300 to over 500 c are determined close to the multiple slip surfaces within the decollement since it is impossible to tie a specific slip surface to a certain earthquake thermal evidence for the cumulative effect of several earthquakes is unveiled this as yet preliminary rock magnetic geothermometer would be a useful tool to detect seismic heating along faults that experienced medium temperature rise a range which is difficult to assess with other approaches

reaction kinetics of alkenone and n alkane thermal alteration at seismic timescales recent experiments and field observations have indicated that biomarker molecules can react over short timescales relevant to seismic slip thereby making these compounds a useful tool in studying temperature rise in fault zones however short timescale biomarker reaction kinetics studies have previously focused on compounds that have already experienced burial heating here we present a set of hydrous pyrolysis experiments on pleistocene aged shallow marine sediment to develop the reaction kinetics of long chain alkenone destruction change in the alkenone unsaturation ratio uk 37 and change in the n alkane chain length distribution our results show that biomarker thermal maturity provides a useful method for detecting temperature rise in the shallow reaches of faults such as subduction zone trench environments through the course of our work we also noted the alteration of total alkenone concentrations and uk 37 values in crushed sediments stored dry at room temperature for durations of months to years but not in the solvent extracts of these materials this result though parenthetical for our work in fault zones has important implications for proper storage of sedimentary samples to be used for alkenone paleotemperature and productivity analysis this article is protected by copyright all rights reserved

energy partitioning during seismic slip in pseudotachylyte bearing faults gole larghe fault adamello italy thedeterminationoftheearthquakeenergybudgetremainsachallengingissueforearthscientists asunderstandingthepartitioningofenergyisa keytowardsthe understandingthe physicsofearthquakes here weestimatethe partitionofthe mechanical workdensity intoheatandsurfaceenergy energyrequiredtocreatenewfracturesurface duringseismicsliponalocationalongafault earthquakeenergypartitioningisdeterminedfromfield and microstructural analyses of a fault segment decorated by pseudotachylyte solidified friction induced melt produced during seismic slip exhumed from a depth of 10 km typical for earthquake hypocenters in the continental crust frictional heat per unit fault area estimated from the thickness of pseudotachylytes is 27 mj m 2 surface energy estimated from microcrack density inside clast i e cracked grains entrapped in the pseudotachylyte and in the fault wall rock ranges between 0 10 and 0 85 mj m 2 our estimates for the studied fault segment suggest that 97 99 of the energy was dissipated as heat during seismic slip we conclude that at 10 km depth less than 3 of the total mechanical work density is adsorbed as surface energy on the fault plane during earthquake rupture 2008 elsevier b v all rights reserved

volcanic tremor and plume height hysteresis from pavlof volcano alaska the march 2016 eruption of pavlof volcano alaska produced an ash plume that caused the cancellation of more than 100 flights in north america the eruption generated strong tremor that was recorded by seismic and remote low frequency acoustic infrasound stations including the earthscope transportable array the relationship between the tremor amplitudes and plume height changes considerably between the waxing and waning portions of the eruption similar hysteresis has been observed between seismic river noise and discharge during storms suggesting that flow and erosional processes in both rivers and volcanoes can produce irreversible structural changes that are detectable in geophysical data we propose that the time varying relationship at pavlof arose from changes in the tremor source related to volcanic vent erosion this relationship may improve estimates of volcanic emissions and characterization of eruption size and intensity

extractable organic material in fault zones as a tool to investigate frictional stress abstract the detection of a frictional heating signature is an attractive but elusive way to measure frictional stress on exhumed faults with no evidence of melting we present a new paleothermometer for fault zones that utilizes the thermal maturity of extractable organic material to determine the maximum frictional heating experienced by the fault because there are no retrograde reactions in these organic systems maximum heating is preserved we investigate the punchbowl fault an ancient strand of the san andreas fault in southern california according to the methylphenanthrene index for thermal maturity there is no differential heating between the fault and off fault samples indicating that the fault did not get hotter than the surrounding rock during slip additionally the thermal maturity of the rocks falls within the range of heating expected from the bounds on burial depth and time and adds some constraint to the burial depth range simple heating models indicate that the fault must have had either 1 an extremely low shear stress during slip 2 an active slipping zone thicker than 1 mm or 3 earthquakes smaller than m6 to lack a differential heating signature after 44 km slip

hot faults iridescent slip surfaces with metallic luster document high temperature ancient seismicity in the wasatch fault zone utah usa and localized iridescence in the footwall dam age zone of the wasatch fault utah usa and document elevated temperatures on these faults we propose that the formation of these iridescent slip surfaces requires frictional heat generated at geometric asperities at seismic slip rates wasatch fault zone abstract we document new geological indicators of ancient seismicity in the form of highly reflec tive iridescent hematite coated fault surfaces small faults that cut the paleoproterozoic farmington canyon complex in the footwall damage zone of the brigham city segment of the wasatch fault utah usa are smooth to striated surfaces tens of square centimeters to 30 m 2 in area the dull rusty to high metallic luster and moderate to high gloss surfaces exhibit multicolored elliptical iridescent patches 0 5 3 cm across preexisting hematite crystals were deformed during slip on 1 200 mm thick slip surfaces textural observations x ray diffraction x ray photoelectron spectroscopy electron backscattered diffraction analysis surface metrology and similarity to experimentally formed iridescent spots in rocks and metals indicate that iridescence is associated with high temperature 300 c reduction of iron fe 3 to fe 2 and associated conversion of hematite to magnetite we pro pose that the iridescent slip surfaces in the wasatch fault damage zone are the result of seismic slip and flash heating at asperities along the small faults the thousands of these sur faces represent coseismic or aftershock deformation down to magnitude 3 in the exhumed footwall damage zone of the wasatch fault

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

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

the fate of diamondoids in coals and sedimentary rocks diamondoids were detected in the extracts of a series of coals and rocks varying in maturity lithology source input and depositional environment at the same maturity level diamondoids are generally about a magnitude more abundant in source rocks than in coals the concentrations of diamondoids are maturity dependent however while diamondoids become more abundant with the increasing thermal maturity a diminution in diamondoid concentrations is observed at the maturity value of about r sub o 4 0 in both coals and rocks the occurrence of diamantane destruction at 550 sup o c during pyrolysis suggests that diamondoids may be eventually destroyed at high temperatures in the earth here we propose three main phases of diamondoid life in nature diamondoid generation phase i r sub o 4 0

warm fluid migration along tectonic melanges in the kodiak accretionary complex alaska analyses of methane water fluid inclusions from syntectonic quartz veins in melange boudins of the kodiak accretionary complex alaska indicate fluid temperatures ranging from 215 to 290 c at depths between 10 and 14 km these fluid temperatures are significantly higher than those predicted by conductive heat flow models of subduction zones given the available geological constraints this discrepancy is interpreted as the result of migration of warm fluids from deeper structural levels along active fault zones during subduction related underthrusting of these units this interpretation requires more careful consideration of how migrating fluids affect the general thermal structure of subduction zones

seismic slip propagation to the updip end of plate boundary subduction interface faults vitrinite reflectance geothermometry on integrated ocean drilling program nantro seize cores seismic faulting along subduction type plate boundaries plays a fundamental role in tsunami genesis during the integrated ocean drilling program iodp nankai trough seismogenic zone experiment nantro seize stage 1 the updip ends of plate boundary subduction faults were drilled and cored in the nankai trough offshore japan where repeated large earthquakes and tsunamis have occurred including the a d 1944 tonankai mw 8 1 earthquake samples were obtained from the frontal thrust which connects the deep plate boundary to the seafloor at the toe of the accretionary wedge and from a megasplay fault that branches from the plate boundary decollement the toe of the accretionary wedge has classically been considered aseismic but vitrinite reflectance geothermometry reveals that the two examined fault zones underwent localized temperatures of more than 380 c this suggests that frictional heating occurred along these two fault zones and implies that coseismic slip must have propagated at least one time to the updip end of the megasplay fault and to the toe of the accretionary wedge

an experimental investigation into the role of phyllosilicate content on earthquake propagation during seismic slip in carbonate faults carbonate faults commonly contain small amounts of phyllosilicate in their slip zones due to pressure solution and or clay smear to assess the effect of phyllosilicate content on earthquake propagation in carbonate faults friction experiments were performed at 1 3 m s on end members and mixtures of calcite illite smectite and smectite gouge experiments were performed at 9 mpa normal load under room humidity and water saturated conditions all dry gouges show initial friction values i of 0 51 0 58 followed by slip hardening to peak values of 0 61 0 76 slip weakening then ensues with friction decreasing to steady state values ss of 0 19 0 33 within 0 17 0 58 m of slip contrastingly wet gouges containing 10 50 wt phyllosilicate exhibit i values between 0 07 and 0 52 followed by negligible or no slip hardening rather steady state sliding ss 0 2 is attained almost immediately microstructurally dry gouges show intense cataclasis and wear within localized principal slip zones plus evidence for thermal decomposition of calcite wet gouges exhibit distributed deformation less intense cataclasis and no evidence of thermal decomposition it is proposed that in wet gouges slip is distributed across a network of weak phyllosilicate formed during axial loading compaction prior to shear this explains the 1 subdued cataclasis and associated lack of slip hardening 2 distributed nature of deformation and 3 lack of evidence for thermal decomposition due to low friction and lack of slip localization these findings imply that just 10 phyllosilicate in the slip zone of fluid saturated carbonate faults can 1 dramatically change their frictional behavior facilitating rupture propagation to the surface and 2 significantly lower frictional heating preventing development of microscale seismic markers

energy taken up by co seismic chemical reactions during a large earthquake an example from the 1999 taiwan chi chi earthquake 1 frictional heat in a fault zone during earthquake slip transiently induces chemical reactions that may use energy released during the earthquake we estimated the energy used by such reactions ec by a numerical analysis incorporating frictional heat thermal diffusion chemical kinetics and energy conservation and found that ec has an auto feedback effect that inhibits temperature rise in fault zone during the 1999 taiwan chi chi earthquake estimated ec was 0 43 mj m2 corresponding to 0 79 of the frictional heat generated this low percentage probably reflects the low initial concentrations of reactive materials however in the case of a fault with abundant reactive materials ec could reach 50 of the frictional heat and the auto feedback effect could be large at this case ec is a nonnegligible component on earthquake energy budget and can affect fault mechanics

principal slip zones precursors but not recorders of earthquake slip narrow highly comminuted shear localization features in faults known as principal slip zones pszs are commonly associated with large offset seismogenic faults in this study laboratory friction experiments were performed using shale and slate gouges where deformation was encouraged to localize at the gouge wall rock boundary the slate gouges develop a black narrow psz composed of densely packed submicron particles that appear sintered while the spectator gouge remains largely undeformed these pszs form at subseismic slip velocities of 10 5 m s and with a calculated temperature rise of 3 c instances of velocity weakening friction which is necessary for unstable fault slip are only observed for slate samples with a psz shale gouges however do not develop a psz and exhibit only velocity strengthening frictional behavior the development of a psz may therefore be a prerequisite for future earthquake slip to occur rather than unequivocal evidence of past earthquake slip

hot on the trail coseismic heating on a localized structure along the muddy mountain fault nevada abstract recent advances in the use of thermal proxies to identify past earthquake slip in exhumed faults have created an extraordinary opportunity to map the geometry of past ruptures in unprecedented detail this approach can reveal along strike differences in the structure and speed of earthquake slip here we present organic thermal maturity data collected along the muddy mountain thrust in nevada to investigate where it was within the fault that earthquake slip occurred and whether this is consistent along strike we observe large changes in thermal maturity which represent temperature rise variations along the fault modeling of thermal maturity measurements yield peak temperatures of 760 1090 c where the principal slip zone psz is narrowest 0 8 mm nearby where the psz is thicker 1 5 mm these temperatures did not exceed 500 c based upon estimates of temperature rise within a submillimeter psz mean frictional work during earthquake slip was 6 3 7 1 mjm 2 these results show that thickness of the active slipping zone can vary at small spatial scales and development of a continuously narrow

gouge formation by dynamic pulverization during earthquake rupture it is proposed here that fault gouge forms by rock pulverization within the tip region of a fast propagating earthquake due to the intensity of stress and rates of strain in this zone to examine this mechanism we calculate the deformation conditions of a dynamic shear fracture propagating close to the limiting rayleigh wave velocity the mechanical conditions close to the fracture tip are extreme tensile stresses approach 5 gpa volumetric strain rates exceed 105 s 1 and volumetric expansion alternates with volumetric contraction it is expected that a localized zone a few millimeters wide will be pulverized under these conditions this mechanism of dynamic gouge formation provides new insight to recent observations of the texture of gouge from the san andreas fault zone and from rupture zones in south african mines further as such extreme conditions develop only during fast propagating earthquakes presence or absence of pulverized gouge may serve as an indicator of earthquake propagation velocity

earth science new madrid in motion a new network of geodetic field stations has greatly improved monitoring of relative motion across a seismic zone in the central united states it seems that rapid deformation is occurring across this fault system a series of large earthquakes centred on the town of new madrid in the mississippi valley in the winter of 1811 12 still reverberates in the world of seismology the controversy relates to their origin over 2 000 km from the nearest plate boundary and their relevance to earthquake hazard today the population of new madrid in the early nineteenth century was tiny a similar event today would have much more serious consequences new evidence based on gps data points to the existence of rapid strain rates in the area comparable in magnitude to those across active plate boundaries and consistent with known active faults in the region

seismic slip record in carbonate bearing fault zones an insight from high velocity friction experiments on siderite gouge pseudotachylyte formed by frictional melting has been the only unequivocal evidence of past seismogenic fault slip we report from high velocity friction experiments on siderite bearing gouge that mineral decomposition due to frictional heating also can leave evidence of paleoseismic events along shallow crustal faults other than pseudotachylyte experiments were conducted room dry on simulated gouge composed of siderite or mixture of siderite calcite and quartz initially at room temperature under normal stresses of 0 6 1 3 mpa and at seismic slip rates of 1 3 2 0 m s in all cases gouge exhibited dramatic slip weakening and siderite was decomposed into nanocrystalline magnetite and co 2 gas as confirmed by co 2 measurement x ray diffraction analyses and transmission electron microscopy the weakening was caused by the low frictional strength of ultrafine decomposition products at seismic slip rates magnetite formation during shearing changed gouge color to black and increased magnetic susceptibility by a few orders of magnitude those changes can be recognized in natural fault zones and black gouge in the chelungpu fault zone in taiwan is perhaps such an example thus our results suggest that thermal decomposition in shallow crustal faults can be an important co seismic process not only for dynamic fault weakening but also for leaving seismic slip records

textural record of the seismic cycle strain rate variation in an ancient subduction thrust active faults slip at different rates over the course of the seismic cycle earthquake slip c 1 m s 1 interseismic creep c 10 100 mm year 1 and intermediate rate transients e g afterslip and slow slip events studies of exhumed faults are sometimes able to identify seismic slip surfaces by the presence of frictional melts and slow creep by textures diagnostic of rate limited plastic processes the pasagshak point thrust preserves three distinct fault rock textures which are mutually cross cutting and can be correlated to different strain rates ultrafine grained black fault rocks including pseudotachylyte were formed during seismic slip on layers up to 30 cm thick well organized s c cataclasites 7 31 m thick were formed by slow creep with pressure solution as a dominant rate limiting mechanism these must have formed at strain rates consistent with long term plate boundary motion but solution creep healing acted to reduce porosity of the cataclasites and eventually restricted fluid connectivity such that creep by this mechanism could not continue disorganized non foliated rounded clast cataclasites were formed at shear rates faster than solution creep and are interpreted as representing shear at intermediate strain rates these could have formed during afterslip or delocalization of slip associated with an earthquake rupture

is the earth lazy a review of work minimization in fault evolution abstract the principle of work minimization has been used in various forms to account for the development of active fault systems within a wide range of tectonic settings we review the successes challenges and implications learned from previous applications of work minimization examination of the energy budget provides insight into the competing influences of different processes within fault systems at a variety of scales we present each work budget component with considerations for numerical implementation additionally we demonstrate numerical implementation by solving for the energy budgets and finding the most efficient propagation paths of a joint and several faults consideration of the energy budget captures growth patterns that are consistent with both laboratory observations and theoretical predictions using the energy release rate g unlike using g work minimization is not limited to collinear growth in comparison with predictions using coulomb failure planes work minimization eliminates uncertainty in predicting fault propagation by 1 evaluating the trade off between tensile and shear failure ahead of the fault and 2 avoiding the ambiguity introduced by the two potential coulomb failure planes application of work minimization to faulting demonstrates the effectiveness of this approach in predicting both the orientation and timing of fault propagation

earthquake fracture energy inferred from kinematic rupture models on extended faults 1 we estimate fracture energy on extended faults for several recent earthquakes by retrieving dynamic traction evolution at each point on the fault plane from slip history imaged by inverting ground motion waveforms we define the breakdown work wb as the excess of work over some minimum traction level achieved during slip wb is equivalent to seismological fracture energy g in previous investigations our numerical approach uses slip velocity as a boundary condition on the fault we employ a three dimensional finite difference algorithm to compute the dynamic traction evolution in the time domain during the earthquake rupture we estimate wb by calculating the scalar product between dynamic traction and slip velocity vectors this approach does not require specifying a constitutive law and assuming dynamic traction to be collinear with slip velocity if these vectors are not collinear the inferred breakdown work depends on the initial traction level we show that breakdown work depends on the square of slip the spatial distribution of breakdown work in a single earthquake is strongly correlated with the slip distribution breakdown work density and its integral over the fault breakdown energy scale with seismic moment according to a power law with exponent 0 59 and 1 18 respectively our estimates of breakdown work range between 4 105 and 2 107 j m2 for earthquakes having moment magnitudes between 5 6 and 7 2 we also compare our inferred values with geologic surface energies this comparison might suggest that breakdown work for large earthquakes goes primarily into heat production

shear heat model for gouge free dip slip listric normal faults abstract shear heating due to brittle faulting is important in petroleum geosciences tectonics and seismic studies temporal variation of shear heat in a listric normal fault with a circular arc shaped fault plane is simulated in this work which was not done so far the work is expected to have a far reaching implication in tectonics and petroleum geosciences since listric faults can be closely associated with hydrocarbon reserves e g valdiya and sanwal 2017 for such a fault plane devoid of gouge and any secondary faulting shear heat is proportional to the mass of the hanging wall block the coefficient of friction acting between the hanging wall and the footwall block and radius of the circular arc shear heating intensifies temporally as the hanging wall block slides down and reaches progressively gentler fault dip

record of mega earthquakes in subduction thrusts the black fault rocks of pasagshak point kodiak island alaska on kodiak island alaska decimeterthick black fault rocks are at the core of foliated cataclasites that are tens of meters thick the cataclasites belong to melange zones that are regarded as paleodecollements active at 12 14 km depth and 230 260 c each black layer is mappable for tens of meters along strike the black fault rocks feature a complex layering made at microscale by alternation of granular and crystalline micro textures both composed of micronscale subrounded quartz and plagioclase in an ultrafi ne phyllosilicate rich matrix in the crystalline microlayers tabular zoned micro lites of plagioclase make up much of the matrix no such feldspars have been found in the cataclasite we interpret these crystalline microlayers as pseudotachylytes the granular microlayers show higher grainsize variability crushed microlites and textures typical of fl uidization and granular fl ow deformation crosscutting relationships between granular and crystalline microlayers include fl ow and intrusion structures and mutual brittle truncation this suggests that each decimeters thick composite black fault rock layer records multiple pulses of seismic slip in each pulse ultracomminuted fl uidized material and friction melt formed and deformed together in a ductile fashion brittle truncation by another pulse occurred after solidifi cation of the friction melt and the fl uidized rock x ray powder diffraction xrpd and x ray fl uorescence xrf analyses show that black fault rocks have similar mineral composition and chemical content as the cataclasites the observed systematic chemical differences cannot be explained by bulk or preferential melting of any of the cataclasite components the presence of an open fl uidinfi ltrated system with later alteration of black fault rocks is suggested the geochemical results indicate that these subductionrelated pseudotachylytes differ from those typically described in crystalline rocks and other tectonic settings

hematite fault rock thermochronometry and textures inform fault zone processes abstract minerals on fault surfaces record fluid rock interaction strain and or heat during fault slip fault hosted hematite is amenable to u th he he thermochronometry hematite he dates reflect fault related processes or exhumation depending on hematite growth above or below the grain size controlled closure temperature and processes that promote open system behavior deconvolving these phenomena requires multi scale hematite textural characterization and constraints on the ambient thermal history from conventional thermochronometry two examples of this approach include investigations of hematite coated fault surfaces from exhumed damage zones in the seismically active wasatch fault zone wfz ut and painted canyon fault pcf paralleling the southern san andreas fault mecca hills ca wfz fault mirrors preserve sub m scale polygonal grain textures and hematite he data patterns that together with host rock apatite he data are consistent with localized friction generated heat hematite he loss and hematite recrystallization during damage zone seismicity