aseismic deformation associated with an earthquake swarm in the northern apennines italy analyzing the displacement time series from continuous gps cgps with an independent component analysis we detect a transient deformation signal that correlates both in space and time with a seismic swarm activity maximum m w 3 69 0 09 occurred in the hanging wall of the altotiberina normal fault northern apennines italy in 2013 2014 the geodetic transient lasted 6 months and produced a nw se trending extension of 5 3 mm consistent with the regional tectonic regime the seismicity and the geodetic signal are consistent with slip on two splay faults in the altotiberina fault atf hanging wall comparing the seismic moment associated with the geodetic transient and the seismic events we observe that seismicity accounts for only a fraction of the measured geodetic deformation the combined seismic and aseismic slip decreased the coulomb stress on the locked shallow portion of the atf while the transition region to the creeping section has been loaded

seismic evidence for overpressured subducted oceanic crust and megathrust fault sealing water and hydrous minerals play a key role in geodynamic processes at subduction zones however there are few seismological constraints on the presence of water within the subducting plate audet et al model converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle their observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip this study models converted teleseismic waves to constrain the seismological properties of subducted oceanic crust from the cascadia continental margin to its intersection with the forearc mantle the observations suggest that water is pervasively present in fluid form at high pore pressures indicating that the megathrust is a low permeability boundary these results may hold important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip water and hydrous minerals play a key part in geodynamic processes at subduction zones1 2 3 by weakening the plate boundary aiding slip and permitting subduction and indeed plate tectonics to occur4 the seismological signature of water within the forearc mantle wedge is evident in anomalies with low seismic shear velocity marking serpentinization5 6 7 however seismological observations bearing on the presence of water within the subducting plate itself are less well documented here we use converted teleseismic waves to obtain observations of anomalously high poisson s ratios within the subducted oceanic crust from the cascadia continental margin to its intersection with forearc mantle on the basis of pressure temperature and compositional considerations the elevated poisson s ratios indicate that water is pervasively present in fluid form at pore pressures near lithostatic values combined with observations of a strong negative velocity contrast at the top of the oceanic crust our results imply that the megathrust is a low permeability boundary the transition from a low to high permeability plate interface downdip into the mantle wedge is explained by hydrofracturing of the seal by volume changes across the interface caused by the onset of crustal eclogitization and mantle serpentinization these results may have important implications for our understanding of seismogenesis subduction zone structure and the mechanism of episodic tremor and slip

an approximation for the xu white velocity model in 1995 s xu and r e white described a method for estimating compressional and shear wave velocities of shaley sandstones from porosity and shale content their model was able to predict the effect of increasing clay content on compressional wave velocity observed in laboratory measurements a key step in the xu white method estimates dry rock bulk and shear moduli for the sand shale mixture this step is performed numerically by applying the differential effective medium method to the kuster toksoz equations for ellipsoidal pores this step is computationally intensive using reasonable assumptions about dry rock elastic properties this step can be replaced with a set of approximations for dry rock bulk and shear moduli numerical experiments show an extremely close match between velocities obtained with these approximations and velocities computed with the differential effective medium method these approximations simplify the application of the xu white method and make the method computationally more efficient they also provide insight into the xu white method for example these approximations show how the xu white model is related to the critical porosity model

organic matter cracking a source of fluid overpressure in subducting sediments the pressure of deep fluids in subduction zones is a major control on plate boundary strength and earthquake genesis the record by methane rich fluid inclusions of large 50 100 mpa and instantaneous pressure variations in the shimanto belt japan points to the presence of large fluid overpressure at depth 300 500 mpa 250 c to further analyze the connection between methane and fluid overpressure we determined with rock eval the potential for a worldwide selection of deep seafloor sediments to produce methane as a result of organic matter om cracking due to temperature increase during subduction the principal factor controlling the methanogenesis potential of sediments is om proportion while om nature is only a subordinate factor in turn om proportion is mainly controlled by the organic terrigenous input considering a typical sediment from ocean continent subduction zones containing 0 5 wt of type iii om cracking of om has two major consequences 1 methane is produced in sufficient concentration as to oversaturate the pore filling water the deep fluid in accretionary prisms is therefore a mechanical mixture of water rich and methane rich phases 2 ch4 production can generate large fluid overpressure of the order of several tens of mpa the conditions for these large overpressure are a low permeability of the upper plate 10 km where om thermal cracking occurs at these depths om thermal cracking appears as a source of overpressure larger than the last increments of smectite to illite reaction such large overpressures play potentially a role in facilitating slip along the plate interface conversely the scarcity of earthquakes in ocean ocean subduction zones such as marianna or barbados may be related to the low influx of detrital om and the limited methane overpressure generation at depth

fluid and melt pathways in the central chilean subduction zone near the 2010 maule earthquake 35 36 s as inferred from magnetotelluric data

the mw 8 3 illapel earthquake chile preseismic and postseismic activity associated with hydrated slab structures the accumulated stress in subduction zones is discharged with earthquake and aseismic activity the latter is hosted in rheological complex regions characterized by high pore fluid pressure and is often accompanied by repeated earthquakes and earthquake swarms the spatiotemporal analysis of seismic activity can reveal the presence of aseismic transients associated with large earthquakes here we study 20 years of seismicity prior to and after the m w 8 3 earthquake that occurred in a d 2015 in central chile we identified several earthquake swarms before the main shock and repeating aftershocks at the border of the main slip area spatial clustering of the seismic activity shares similar orientation with the main fracture zones observed on the outer rise of the subducting nazca plate our findings suggest that the fracture zones enclosing the rupture are playing a major role in accommodating the pre and post main shock stress evolution we further recognize how fracture regions have acted as barriers to the propagation of large earthquakes in the region

brittle deformation during alpine basal accretion and the origin of seismicity nests above the subduction interface geophysical observations on active subduction zones have evidenced high seismicity clusters at 20 40 km depth in the fore arc region whose origin remains controversial we report here field observations of pervasive pseudotachylyte networks interpreted as evidence for paleo seismicity in the now exhumed valpelline continental unit dent blanche complex nw alps italy a tectonic sliver accreted to the upper plate at c 30 km depth during the paleocene alpine subduction pre alpine granulite facies paragneiss from the core of the valpelline unit are crosscut by widespread mm to cm thick pseudotachylyte veins co seismic heating and subsequent cooling led to the formation of ti rich garnet rims ilmenite needles ca rich plagioclase biotite microliths and hercynite micro crystals 39ar 40ar dating yields a 51 54 ma age range for these veins thus suggesting that frictional melting events occurred near peak burial conditions while the valpelline unit was already inserted inside the duplex structure in contrast the base of the valpelline unit underwent synchronous ductile and brittle seismic deformation under water bearing conditions followed by a re equilibration at c 40 ma 39ar 40ar on retrograded pseudotachylyte veins during exhumation related deformation calculated rheological profiles suggest that pseudotachylyte veins from the dry core of the granulite unit record upper plate micro seismicity mw 2 3 formed under very high differential stresses 500 mpa while the sheared base of the unit underwent repeated brittle ductile deformation at much lower differential stresses 40 mpa in a fluid saturated environment these results demonstrate that some of the seismicity clusters nested along and above the plate interface may reflect the presence of stiff tectonic slivers rheologically analogous to the valpelline unit acting as repeatedly breaking asperities in the basal accretion region of active subduction zones

empirical relationships among seismic velocity effective pressure porosity and clay content in sandstone we use a multivariate analysis to investigate the influence of effective pressure pe porosity and clay content c on the compressional velocity vp and shear velocity vs of sandstones laboratory measurements on water saturated samples of 64 different sandstones provide a large data set that was analyzed statistically for each sample relationships between effective pressure and vp and vs have been determined all samples were well fit by relationships that have an exponential increase in velocity at low pe tapering to a linear increase with pe for pe greater than 0 2 kbar there are differences in the pressure dependences of velocity for different rocks particularly at very low pressures however the differences cannot be attributed to or c for the combined set of measurements from all samples the best fitting formulations are vp 5 77 6 94 1 73c 0 446 pe e 16 7pe and vs 3 70 4 94 1 57c 0 361 pe e 16 7pe while this is admittedly a very simplified parameterization it is remarkable how well

seismo hydro mechanical modelling of the seismic cycle methodology and implications for subduction zone seismicity abstract slip accommodation in subduction zones ranges from aseismic slip phenomena to regular megathrust earthquakes and strongly depends on pore fluid pressure we develop a new fully coupled poro visco elasto plastic seismo hydro mechanical numerical model allowing for coupled modelling of tectonic and seismic processes in the presence of fluids a combination of fully staggered finite differences and marker in cell techniques is used to solve mass and momentum conservation equations for solid matrix and fluid coupled to a poro visco elasto plastic rheological constitutive relationship brittle plastic deformation is resolved through global picard iterations and adaptive time stepping is introduced to resolve time scales from milliseconds to thousands of years involved in the hydro mechanical seismic cycle we demonstrate how and why the presence of pervasive fluid flow in the deforming poro visco elasto plastic subduction interface causes localisation of deformation and nucleation of seismic events with slip rate up to m s the nucleation of fault slip is controlled by rapid fluid pressure increase due to visco plastic compaction of a spontaneously forming fault balanced by the simultaneous elastic decompaction of deforming pores inside the fault subsequent post and inter seismic slow fluid pressure release by elastic compaction of the stressed pores allows recovery of subduction interface strength the events nucleate downdip in the brittle ductile transition zone and propagate updip in form of highly localized spontaneous ruptures the model reproduces the broad spectrum of transient phenomena ranging from slow slip to seismic ruptures on a subduction interface with homogenous elastic and frictional properties that do not depend on slip rate the degree of locking of the megathrust interface the coseismic stress drop and the dominant slip regime during subduction are critically dependent on effective large scale and long term rock permeability a decrease of permeability leads to a decrease of degree of locking leading to smaller stress drop and enhancing the occurrence of stable aseismic slip

coseismic and postseismic slip of the 2005 m w 8 6 nias simeulue earthquake spatial overlap and localized viscoelastic flow

dynamics of a velocity strengthening fault region implications for slow earthquakes and postseismic slip we consider the effect of permanent stress changes on a velocity strengthening rate and state fault through numerical simulations and analytical results on 1 d 2 d and 3 d models we show that slip transients can be triggered by perturbations of size roughly larger than lb gdc b where g is the shear modulus dc and b are the characteristic slip distance and the coefficient of the evolution effect of rate and state friction respectively and is the effective normal stress perturbations that increase the coulomb stress lead to the strongest transients but creep bursts can also be triggered by perturbations that decrease the coulomb stress in the latter case peak slip velocity is attained long after the perturbation so that it may be difficult in practice to identify their origin the evolution of slip in a creep transient shares many features with the nucleation process of a rate and state weakening fault slip initially localizes over a region of size not smaller than lb and then accelerates transiently and finally expands as a quasi static propagating crack the characteristic size lb implies a constraint on the grid resolution of numerical models even on strengthening faults that is more stringent than classical criteria in the transition zone between the velocity weakening and strengthening regions the peak slip velocity may be arbitrarily large and may approach seismic slip velocities postseismic slip may represent the response of the creeping parts of the fault to a stress perturbation of large scale comparable to the extent of the main shock rupture and high amplitude while slow earthquakes may represent the response of the creeping zones to a more localized stress perturbation our results indicate that superficial afterslip observed at usually seismogenic depths is governed by a rate strengthening rheology and is not likely to correspond to stable weakening zones the predictions of the full rate and state framework reduce to a pure velocity strengthening law on a timescale longer than the duration of the acceleration transient only when the triggering perturbation extends over length scales much larger than lb

reviewing megathrust slip behavior for recent mw 8 0 earthquakes along the peru chilean margin from satellite goce gravity field derivatives abstract the characterization of a seismogenic zone associated with the rupture process that occurs during great megathrust earthquakes has been approached from different perspectives different studies lightened the structural complexity and compositional heterogeneity of the interplate region in this work we address this relationship from the analysis of density contrasts provided by satellite gravity data and comparing these results with slip behavior along the rupture zone we performed the calculation of gravity anomalies and gradients both corrected by the effect of topography and sediments then we analyzed this relation with the rupture zones of four megathrust earthquakes mw 8 along the peru chilean coast associated with the largest earthquakes that occurred in the last years along this setting finding that the maximum vertical displacements were located close to gravity minimums in the forearc zone we finally obtained density models by inverting four trench parallel profiles from the gravity disturbance finding low density contrasts related to the maximum slips and high density contrasts at its edges related to a decrease of the displacement or to the lateral ending of the rupture the along strike seismic segmentation observed previously in the gravity derivatives is also observed along dip being slip increased at gravity lows and arrested at gravity highs probably indicating that the forearc structure plays a key role in across strike rupture behavior in depth our results agree with the hypothesis that persistent tectonic features modeled at a high degree by the oceanic plate morphology may control strain accumulation and release along the megathrust

chilean megathrust earthquake recurrence linked to frictional contrast at depth fundamental processes of the seismic cycle in subduction zones including those controlling the recurrence and size of great earthquakes are still poorly understood here by studying the 2016 earthquake in southern chile the first large event within the rupture zone of the 1960 earthquake moment magnitude mw 9 5 we show that the frictional zonation of the plate interface fault at depth mechanically controls the timing of more frequent moderate size deep events mw 8 5 we model the evolution of stress build up for a seismogenic zone with heterogeneous friction to examine the link between the 2016 and 1960 earthquakes our results suggest that the deeper segments of the seismogenic megathrust are weaker and interseismically loaded by a more strongly coupled shallower asperity deeper segments fail earlier 60 yr recurrence producing moderate size events that precede the failure of the shallower region which fails in a great earthquake recurrence 110 yr we interpret the contrasting frictional strength and lag time between deeper and shallower earthquakes to be controlled by variations in pore fluid pressure our integrated analysis strengthens understanding of the mechanics and timing of great megathrust earthquakes and therefore could aid in the seismic hazard assessment of other subduction zones the recurrence time of megathrust earthquakes in chile may be controlled by frictional contrasts at depth according to analyses of stress build up and release related to the december 2016 southern chile earthquake

predicting imminence of analog megathrust earthquakes with machine learning implications for monitoring subduction zones abstract subduction zones are monitored using space geodesy with increasing resolution with the aim of better capturing the deformation accompanying the seismic cycle here we investigate data characteristics that maximize the performance of a machine learning binary classifier predicting slip event imminence we overcome the scarcity of recorded instances from real subduction zones using data from a seismotectonic analog model monitored with a spatially dense continuously recording onshore geodetic network we show that a 70 85 km wide coastal swath recording interseismic deformation gives the most important information on slip imminence prediction performances are mainly influenced by the alarm duration amount of time that we consider an event as imminent with density of stations and record length playing a secondary role the techniques developed in this study are most likely applicable in regions of slow earthquakes where stick slip like failures occur at time intervals of months to years

shear stresses on megathrusts implications for mountain building behind subduction zones 1 shear stresses on a subduction megathrust play an important role in determining the forces available for mountain building adjacent to a subduction zone in this study the temperatures and shear stresses on megathrusts in 11 subduction zones around the pacific rim hikurangi tonga izu ogasawara western nankai northeastern japan aleutians western alaska cascadia northern chile southern chile and se asia northern sumatra have been determined the main constraint is that vertical normal stresses beneath the highlands behind the subduction zone are nearly equal to horizontal normal stresses in the plane of a trench or arc normal section for a typical brittle and ductile megathrust rheology frictional shear stress gz for depth z and ductile shear stress a exp b rt at temperature t where a b are rheological parameters treated as constants rheological constants common to all the megathrusts crust mantle b are determined by simultaneously solving for the force balance in the overlying wedge and megathrust thermal structure using a simplex minimization algorithm taking account of the induced mantle corner flow at depth 65 15 km 2 and constant radiogenic heating 0 65 0 3 w m 3 2 throughout the crust the a constants are solved individually for each subduction zone assuming that the maximum depth of interplate slip earthquakes marks the brittle ductile transition the best fit solution shows two groupings of megathrusts with most subduction zones having a low mean shear stress in the range 7 15 mpa crust 0 032 0 006 mantle 0 019 0 004 and unable to support elevations 2 5 km for a typical frictional sliding coefficient 0 5 the low effective coefficients of friction suggest high pore fluid pressures at 95 lithostatic pressure tonga and northern chile require higher shear stresses with crust 0 095 0 024 mantle 0 026 0 007 suggesting slightly lower pore fluid pressures at 81 lithostatic ductile shear in the crust is poorly resolved but in the mantle appears to show a strong power law dependency with b 36 18 kj mol 1 amantle values are sensitive to the precise value of b but are in the range 1 20 kpa the power law exponent n for mantle flow is poorly constrained but is likely to be large n 4 the brittle ductile transition in the crust occurs at temperatures in the range 370 c 512 c usually close to the base of the crust and in the mantle at much lower temperatures 180 c 300 c possibly reflecting a marked change in pore fluid pressure or quasi ductile and subfrictional properties in subduction zones where the subducted slab is older than 50 ma a significant proportion of the integrated shear force on the megathrust is taken up where it cuts the mantle and temperatures are 300 c in much younger subduction zones the stress transmission is confined mainly to the crust the shear stresses particularly in the crust may be kept low by some sort of lubricant such as abundant water rich trench fill which lowers the frictional sliding coefficient or effective viscosity and or raises pore fluid pressure the unusual high stress subduction zone in northern chile lacks significant trench fill and may be poorly lubricated with a mean shear stress 37 mpa required to support elevations 4 km in the high andes however where the crust is thin in sediment starved and poorly lubricated subduction zones such as tonga the mean shear stress will still be low sediment may lubricate megathrusts accommodating underthrusting of continental crust such as in the himalayas or eastern central andes which have a low mean shear stress 15 mpa

a high resolution time variable afterslip model for the 2010 maule mw 8 8 chile megathrust earthquake the excellent spatial coverage of continuous gps stations in the region affected by the maule mw 8 8 2010 earthquake combined with the proximity of the coast to the seismogenic zone allows us to model megathrust afterslip on the plate interface with unprecedented detail we invert post seismic observations from continuous gps sites to derive a time variable model of the first 420 d of afterslip we also invert co seismic gps displacements to create a new co seismic slip model the afterslip pattern appears to be transient and non stationary with the cumulative afterslip pattern being formed from afterslip pulses changes in static stress on the plate interface from the co and post seismic slip cannot solely explain the aftershock patterns suggesting that another process perhaps fluid related is controlling the lower magnitude aftershocks we use aftershock data to quantify the seismic coupling distribution during the post seismic phase comparison of the post seismic behaviour to interseismic locking suggests that highly locked regions do not necessarily behave as rate weakening in the post seismic period by comparing the inter seismic locking co seismic slip afterslip and aftershocks we attempt to classify the heterogeneous frictional behaviour of the plate interface

upper lithospheric structure of the subduction zone offshore of southern arauco peninsula chile at 38 s velocities 8 4 km s 1 in the trench outer rise area the top of incoming oceanic plate is pervasively fractured and likely hydrated as shown by extensional faults horst and graben structures and a reduction of both crustal and mantle velocities these slow velocities are interpreted in terms of extensional bending related faulting leading to fracturing and hydration in the upper part of the oceanic lithosphere the incoming mocha fz coincides with an area of even slower velocities and thinning of the oceanic crust 10 15 thinning suggesting that the incoming fracture zone may enhance the flux of chemically bound water into the subduction zone slow mantle velocities occur down to a maximum depth of 6 8 km into the upper mantle where mantle temperatures are estimated to be 400 430c in the overriding plate the tomographic model reveals two prominent velocity transition zones characterized by steep lateral velocity gradients resulting in a seismic segmentation of the marine fore arc the margin is composed of three main domains 1 a 20 km wide frontal prism below the continental slope with vp 3 5 km s 1 2 a 50 km area with vp 4 5 5 5 km s 1 interpreted as a paleoaccretionary complex and 3 the seaward edge of the paleozoic continental framework with vp 6 0 km s 1 frontal prism velocities are noticeably lower than those found in the northern erosional chile margin confirming recent accretionary processes in south central chile

interseismic coupling and asperity distribution along the kamchatka subduction zone 1 gps measurements of interseismic horizontal surface velocities reveal the degree of kinematic coupling of the plate boundary thrust along the kamchatka subduction zone from about 51 degrees to 57 degrees n latitude inversions for the distribution of aseismic slip rate along the similar to 15 degrees nw dipping underthrust suggest a nonslipping plate interface in southern kamchatka above similar to 50 km depth along the segment that ruptured in the m w 9 1952 earthquake north of similar to 53 degrees n the subduction interface experiences significant aseismic slip consistent with the lower seismic moment release in m 8 5 earthquakes along this portion of the subduction zone the gps velocities are consistent with a boundary element forward model in which historic earthquake rupture zones are represented as locked asperities surrounded by a zero shear stress subduction interface loaded by plate convergence models in which the complete rupture zones of historic earthquakes are considered locked greatly overpredict the degree of kinematic coupling reducing the area of the locked model asperities to the central 25 area of historic rupture zones fits the data well suggesting that large earthquakes involve small fully locked core asperities surrounded by conditionally stable portions of the plate interface areas of low aseismic slip rate appear to be roughly correlated with areas of low isostatic gravity anomalies over offshore forearc basins while less coupled portions of the kamchatka subduction zone coincide with high gravity anomalies offshore of two peninsulas possibly related to the subduction of the emperor meji seamount chain and the kruzenstern fracture zone

crustal deformation dynamics and stress evolution during seamount subduction high resolution 3 d numerical modeling funding was received from the people programme marie curie actions of the european union s seventh framework programme fp7 2007 2013 under rea grant agreement 604713 zip zooming in between plates v s and c r r acknowledge financial support received through the hades project ctm2011 30400 c01 and ctm2011 30400 c02 funded by spanish mineco

segmentation and supercycles a catalog of earthquake rupture patterns from the sumatran sunda megathrust and other well studied faults worldwide abstract after more than 100 years of earthquake research earthquake forecasting which relies on knowledge of past fault rupture patterns has become the foundation for societal defense against seismic natural disasters a concept that has come into focus more recently is that rupture segmentation and cyclicity can be complex and that a characteristic earthquake model is too simple to adequately describe much of fault behavior nevertheless recognizable patterns in earthquake recurrence emerge from long high resolution spatially distributed chronologies researchers now seek to discover the maximum minimum and typical rupture areas the distribution variability and spatial applicability of recurrence intervals and patterns of earthquake clustering in space and time the term supercycle has been used to describe repeating longer periods of elastic strain accumulation and release that involve multiple fault ruptures however this term has become very broadly applied lumping together several distinct phenomena that likely have disparate underlying causes we divide earthquake cycle behavior into four major classes that have different implications for seismic hazard and fault mechanics 1 quasi periodic similar ruptures 2 clustered similar ruptures 3 clustered complementary ruptures rupture cascades and 4 superimposed cycles segmentation is likewise an ambiguous term we identify master segments and asperities as defined by barriers to fault rupture these barriers may be persistent rarely or never traversed frequent occasionally traversed or ephemeral changing location from cycle to cycle we compile a catalog of the historical and paleoseismic evidence that currently exists for each of these types of behavior on major well studied faults worldwide due to the unique level of paleoseismic and paleogeodetic detail provided by the coral microatoll technique the sumatran sunda megathrust provides one of the most complete records over multiple earthquake rupture cycles long historical records of earthquakes along the south american and japanese subduction zones are also vital contributors to our catalog along with additional data compiled from subduction zones in cascadia alaska and middle america as well as the north anatolian and dead sea strike slip faults in the middle east we find that persistent and frequent barriers rupture cascades superimposed cycles and quasi periodic similar ruptures are common features of most major faults clustered similar ruptures do not appear to be common but broad overlap zones between neighboring segments do occur barrier regions accommodate slip through reduced interseismic coupling slow slip events and or smaller more localized ruptures and are frequently associated with structural features such as subducting seafloor relief or fault trace discontinuities this catalog of observations provides a basis for exploring and modeling root causes of rupture segmentation and cycle behavior we expect that researchers will recognize similar behavior styles on other major faults around the world

hydroxyl oh production on airless planetary bodies evidence from h d ion beam experiments abstract the hypothesis that bombardment of lunar soil with solar wind protons might form hydroxyl oh and perhaps hoh has been tested by experiments with apollo 16 highlands and apollo 17 mare soils pre dried soils 500 c were bombarded with 1 1 kev protons and deuterons and provide unambiguous evidence for the formation of oh or od in both samples this hypothesis further predicts the formation of hydroxyl oh on other airless planetary asteroidal bodies with a sufficient solar wind flux deuteron implantation of unaltered lunar soils and a heat treated plagioclase specimen cause simultaneous oh depletion and od formation ion bombardment of lunar soils simulates the dynamic process of hydroxyl formation and may also deplete intrinsic oh thereby effectively contributing to the day night diurnal variability of oh reported by sunshine et al 2009 our results emphasize the need to use lunar soils with space weathered exteriors in laboratory simulations of the solar wind infrared spectra of hydrogen ion beam implanted soils are similar to spectra obtained at relab brown univ and to those observed by remote sensing confirming the solar wind hypothesis

investigating the final seismic swarm before the iquique pisagua 2014 mw 8 1 by comparison of continuous gps and seismic foreshock data preexisting networks of seismometers and continuous gps in northern chile successfully captured surface motions and seismicity leading up to the 1 april mw 8 1 here we compare continuous gps cgps with predictions of seismic dislocations for the final foreshock swarm beginning with the 16 march mw 6 7 results show that the cumulative cgps motion can be largely explained by seismic slip because evolutions of cgps positions for most stations stay within the ranges of seismic predictions given sensible ranges of assumed source errors however cgps motions between 18 21 and 25 31 march outpace seismic predictions supporting the existence of aseismic transients that were most probably the afterslip from preceding bursts of seismicity a parameter search reveals that the 16 march mw 6 7 cgps displacements can be recreated with a fault plane significantly rotated anticlockwise from the strike of the plate interface suggesting that failure was on a structure other than the plate interface

permeability control on transient slip weakening during gypsum dehydration implications for earthquakes in subduction zones a conflict has emerged from recent laboratory experiments regarding the question of whether or not dehydration reactions can promote unstable slip in subduction zones leading to earthquakes although reactions produce mechanical weakening due to pore fluid pressure increase this weakening has been associated with both stable and unstable slip here new results monitoring strength permeability pore fluid pressure reaction progress and microstructural evolution during dehydration reactions are presented to identify the conditions necessary for mechanical instability triaxial experiments are conducted using gypsum and a direct shear sample assembly with constant normal stress that allows the measurement of permeability during sliding tests are conducted with temperature ramp from 70 to 150 c and with different effective confining pressures 50 100 and 150 mpa and velocities 0 1 and 0 4 m s 1 results show that gypsum dehydration to bassanite induces transient stable slip weakening that is controlled by pore fluid pressure and permeability evolution at the onset of dehydration the low permeability promoted by pore compaction induces pore fluid pressure build up and stable slip weakening the increase of bassanite content during the reaction shows clear evidence of dehydration related with the development of r1 riedel shears and p foliation planes where bassanite is preferentially localized along these structures the continued production of bassanite which is stronger than gypsum provides a supporting framework for newly formed pores thus resulting in permeability increase pore fluid pressure drop and fault strength increase after dehydration reaction deformation is characterized by unstable slip on the fully dehydrated reaction product controlled by the transition from velocity strengthening to velocity weakening behaviour of bassanite at temperature above 140 c and the localization of deformation along narrow y shear planes this study highlights the generic conditions required to trigger instabilities during dehydration reactions it shows that pore fluid pressure build up during dehydration reactions associated with the localization of a velocity weakening reacting or dehydrated phase along shear planes is necessary for earthquake triggering

from soft sediment deformation to fluid assisted faulting in the shallow part of a subduction megathrust analogue the sestola vidiciatico tectonic unit northern apennines italy

effective stress and pore pressure in the nankai accretionary prism off the muroto peninsula southwestern japan 1 we developed a theoretical method for predicting effective stress and pore pressure based on rock physics model we applied the method to reveal the pore pressure distribution within the nankai accretionary prism off southwestern japan and to investigate variations in pore pressure associated with evolution of the plate boundary decollement from the crack aspect ratio spectrum estimated from laboratory and well log data we calculated a theoretical relationship between acoustic velocity and mean effective stress by using differential effective medium theory by iteratively fitting the theoretically calculated velocity to the seismic velocities derived from 3d tomographic inversion we estimated in situ mean effective stress within the accretionary prism pore pressure is then the difference between the effective stress and the confining stress when we calculated pore pressure we considered compressive state of stress in the accretionary prism our results confirm that pore fluid pressure is high within the subducting sedimentary sequence below the decollement we determined a normalized pore pressure ratio of 0 4 0 7 abnormal pore pressures develop in the under thrust sequence as a result of the increase in overburden load because of the thickened overlying prism and a low permeability barrier across the decollement overpressuring within the accreted sequence is initiated at the deformation front and proceeds landward the increase in horizontal compaction within the accreted sequence may raise pore pressures within the accreted sequence and the pore pressure mean effective stress contrast at the decollement becomes smaller landward of the deformation front

toward understanding tectonic control on the mw 8 8 2010 maule chile earthquake the maule earthquake of 27th february 2010 m w 8 8 affected similar to 500 km of the nazca south america plate boundary in south central chile producing spectacular crustal deformation here we present a detailed estimate of static coseismic surface offsets as measured by survey and continuous gps both in near and far field regions earthquake slip along the megathrust has been inferred from a joint inversion of our new data together with published gps insar and land level changes data using green s functions generated by a spherical finite element model with realistic subduction zone geometry the combination of the data sets provided a good resolution indicating that most of the slip was well resolved coseismic slip was concentrated north of the epicenter with up to 16 m of slip whereas to the south it reached over 10 m within two minor patches a comparison of coseismic slip with the slip deficit accumulated since the last great earthquake in 1835 suggests that the 2010 event closed a mature seismic gap slip deficit distribution shows an apparent local overshoot that highlight cycle to cycle variability which has to be taken into account when anticipating future events from interseismic observations rupture propagation was obviously not affected by bathymetric features of the incoming plate instead splay faults in the upper plate seem to have limited rupture propagation in the updip and along strike directions additionally we found that along strike gradients in slip are spatially correlated with geometrical inflections of the megathrust our study suggests that persistent tectonic features may control strain accumulation and release along subduction megathrusts c 2012 elsevier b v all rights reserved

tectonic slicing of subducting oceanic crust along plate interfaces numerical modeling multikilometer sized slivers of high pressure low temperature metamorphic oceanic crust and mantle are observed in many mountain belts these blueschist and eclogite units were detached from the descending plate during subduction large scale thermo mechanical numerical models based on finite difference marker in cell staggered grid technique are implemented to investigate slicing processes that lead to the detachment of oceanic slivers and their exhumation before the onset of the continental collision phase in particular we investigate the role of the serpentinized subcrustal slab mantle in the mechanisms of shallow and deep crustal slicing results show that spatially homogeneous serpentinization of the sub moho slab mantle leads to complete accretion of oceanic crust within the accretionary wedge spatially discontinuous serpentinization of the slab mantle in form of unconnected patches can lead to shallow slicing of the oceanic crust below the accretionary wedge and to its deep slicing at mantle depths depending on the patch length slab angle convergence velocity and continental geothermal gradient p t paths obtained in this study are compared to natural examples of shallow slicing of the crescent terrane below vancouver island and deeply sliced crust of the lago superiore and saas zermatt units in the western alps

combining gps and repeating earthquakes for a high resolution analysis of subduction zone coupling abstract increasingly complex spatiotemporal patterns of subduction zone coupling are being revealed by geodetic and seismic observations understanding the mechanisms which control it is useful for improving seismic hazard assessments gps and characteristically repeating earthquakes cres are complementary datasets for monitoring aseismic slip here both of them are combined to estimate the rate and distribution of creep on the northeast japan subduction zone between 21 march 1996 and 24 september 2003 we find that the majority of the upper part at 0 30 km depth remains locked there are three regions creeping at 7 8 cm yr distributed along strike at 40 70 km depth we observe that these creeping regions occur in areas of low effective pressure and reduced porosity which are inferred from vp and vs velocities moreover an area of high clay content and high effective pressure coincides with the rupture area of the tohoku oki earthquake we discuss these results in the context of potential mechanisms governing creep in northeast japan our results highlight the benefits of combining gps and cres for advancing our understanding of the seismic cycle in subduction zones

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

earthquake nucleation in weak subducted carbonates ocean floor carbonate and clay rich sediments form major inputs to subduction zones especially at low latitude convergent plate margins therefore knowledge of their frictional behaviour is fundamental for understanding plate boundary earthquakes here we report results of mechanical tests performed on simulated fault gouges prepared from ocean floor carbonates and clays cored during iodp drilling offshore costa rica clay rich gouges show internal friction coefficients that is the slope of linearized shear stress versus normal stress data of int 0 44 0 56 irrespective of temperature and pore fluid pressure pf by contrast int for the carbonate gouge strongly depends on temperature and pore fluid pressure with int decreasing dramatically from 0 84 at room temperature and pf 20 mpa to 0 27 at t 140 c and pf 120 mpa this effect provides a fundamental mechanism of shear localization and earthquake generation in subduction zones and makes carbonates likely nucleation sites for plate boundary earthquakes our results imply that rupture nucleation is prompted by a combination of temperature controlled frictional instability and temperature and pore pressure dependent weakening of calcareous fault gouges

heterogeneous coupling of the sumatran megathrust constrained by geodetic and paleogeodetic measurements geodetic and paleogeodetic measurements of interseismic strain above the sumatran portion of the sunda subduction zone reveal a heterogeneous pattern of coupling annual banding in corals provides vertical rates of deformation spanning the last half of the 20th century and repeated gps surveys between 1991 and 2001 and continuous measurements at gps stations operated since 2002 provide horizontal velocities near the equator the megathrust is locked over a narrow width of only a few tens of kilometers in contrast the locked fault zone is up to about 175 km wide in areas where great interplate earthquakes have occurred in the past formal inversion of the data reveals that these strongly coupled patches are roughly coincident with asperities that ruptured during these events the correlation is most spectacular for rupture of the m w 8 7 nias simeulue earthquake of 2005 which released half of the moment deficit that had accumulated since its previous rupture in 1861 suggesting that this earthquake was overdue beneath the mentawai islands strong coupling is observed within the overlapping rupture areas of the great earthquakes of 1797 and 1833 the accumulated slip deficit since these events is slowly reaching the amount of slip that occurred during the 1833 earthquake but already exceeds the slip that occurred during the 1797 earthquake thus rerupture of part of the mentawai patch in september 2007 was not a surprise in contrast coupling is low below the batu islands near the equator and around enggano island at about 5 s where only moderate earthquakes m w 8 0 have occurred in the past two centuries the correlation of large seismic asperities with patches that are locked during the interseismic period suggests that they are persistent features this interpretation is reinforced by the fact that the large locked patches and great ruptures occur beneath persistent geomorphologic features the largest outer arc islands depth and convergence rate dependent temperature might influence the pattern of coupling through its effect on the rheology of the plate interface but other influences are required to account for the observed along strike heterogeneity of coupling in particular subduction of the investigator fracture zone could be the cause for the low coupling near the equator

hydrologic control of forearc strength and seismicity in the costa rican subduction zone the subduction zone beneath costa rica experiences infrequent large earthquakes in its northwestern part whereas slow slip dominates in the southeast seismic data reveal a disparity in fluid accumulation in the overriding continental crust that correlates with this change in seismic behaviour implying that spatial gradients in fluid content may control subduction zone seismicity

spatial correlation of interseismic coupling and coseismic rupture extent of the 2011 mw 9 0 tohoku oki earthquake 1 imaging the extent to which the rupture areas of great earthquakes coincide with regions of pre seismic interplate coupling is central to understanding patterns of strain accumulation and release through the earthquake cycle both geodetic and seismic estimates of the coseismic rupture extent for the march 11 2011 mw 8 9 9 0 earthquake tohoku oki earthquake may be spatially correlated 0 26 0 05 to 0 82 0 05 with a region estimated to be partially to fully coupled in the interseismic period preceding the earthquake though there is substantial variation in the estimated distribution and magnitude of coseismic slip the 400 km long region estimated to have slipped 4 m corresponds to an area of the subduction zone interface that was coupled at 30 of long term plate convergence rate with peak slip near a region coupled 80 the northern termination of rupture is collocated with a region of relatively low 20 interseismic coupling near the epicenter of the 1994 mw 7 6 sanriku oki earthquake and near a region of potential long term low coupling or ongoing slow slip slip on the subduction interface beneath the coastline 40 50 km depth is best constrained by the land based gps data and least constrained on the shallowest portion of the plate interface due to the 230 km distance between geodetic observations and the japan trench

structure of the seismogenic zone of the southcentral chilean margin revealed by local earthquake traveltime tomography we use traveltime data of local earthquakes and controlled sources observed by a large temporary amphibious seismic network to reveal the anatomy of the southcentral chilean subduction zone 37 39 s between the trench and the magmatic arc at this location the giant 1960 earthquake m 9 5 nucleated and ruptured almost 1000 km of the subduction megathrust for the three dimensional tomographic inversion we used 17 148 p wave and 10 049 s wave arrival time readings from 439 local earthquakes and 94 shots the resolution of the tomographic images was explored by analyzing the model resolution matrix and conducting extensive numerical tests the downgoing lithosphere is delineated by high seismic p wave velocities high vp vs ratio in the subducting slab reflects hydrated oceanic crust and serpentinized uppermost oceanic mantle the subducting oceanic crust can be traced down to a depth of 80 km as indicated by a low velocity channel the continental crust extends to approximately a 50 km depth near the intersection with the subducting plate this suggests a wide contact zone between continental and oceanic crust of about 150 km potentially supporting the development of large asperities eastward the crustal thickness decreases again to a minimum of about a 30 km depth relatively low vp vs at the base of the forearc does not support a large scale serpentinization of the mantle wedge offshore low vp and high vp vs reflect young fluid saturated sediments of forearc basins and the accretionary prism

quantitative relationship between aseismic slip propagation speed and frictional properties recent observations show evidence of propagation of postseismic slip which may contain information about the mechanical properties of faults here we develop a new analytical relationship between the propagation speed of aseismic slip transients and fault frictional properties modeled by a rate and state dependent friction law the relationship explains the propagation speed of afterslip in 3 d numerical simulations to first order based on this relationship we identify systematic dependencies of afterslip propagation speed on effective normal stress and frictional properties the coefficients a and a b which quantify the instantaneous and the steady state velocity dependence of friction respectively and the characteristic slip distance l of fault state evolution lower values of the parameter a a cause faster propagation in areas where the passage of the postseismic slip front induces large shear stress changes compared to a which are typically located near the mainshock rupture in areas where a is small typically more distant from the mainshock afterslip propagation speed is more sensitive to a b the propagation speed is proportional to initial slip velocity and under the condition that loading span is significantly shorter than the passage of postseismic slip inversely proportional to l the relationship developed here should be useful to constrain the frictional properties of faults based on observed propagation speeds independently of rock laboratory experiments which can then be used in predictive numerical simulations of aseismic slip phenomena

constraining the strength of megathrusts from fault geometries and application to the alpine collision zone abstract using coulomb wedge solutions we show that the effective strength of megathrusts b can be determined from the geometry of out of sequence thrusts cutting through an accretionary or orogenic wedge the method is first tested on central chilean margin for which it yields a frictional strength of b 0 053 0 043 0 024 the inferred value agrees well with previous strength estimates and with the tectonic response of the central chilean wedge to 2010 m w 8 8 maule earthquake we then use the approach to constrain the strength of the collision megathrust of the central european alps 30 20 million years ago we find that the collision megathrust had a strength of b 0 065 0 035 0 026 which is similarly low than the strength of subduction megathrusts the result is integrated into a static force balance model to examine potential implications of a weak megathrust for the alpine orogeny the model results suggest that the alpine megathrust supported a mean maximum elevation of 2 000 m and that growth of the wedge up to this elevation supported a switch from contractional to extensional tectonics in the interior of the alps around 20 ma finally using the example of the himalayas we show how the strength of megathrusts may be also derived from the geometry of crustal ramps which provides a valuable alternative if details on out of sequence thrusts are missing

anatomy of a megathrust the 2010 m8 8 maule chile earthquake rupture zone imaged using seismic tomography abstract knowledge of seismic velocities in the seismogenic part of subduction zones can reveal how material properties may influence large ruptures observations of aftershocks that followed the 2010 m w 8 8 maule chile earthquake provide an exceptional dataset to examine the physical properties of a megathrust rupture zone we manually analysed aftershocks from onshore seismic stations and ocean bottom seismometers to derive a 3 d velocity model of the rupture zone using local earthquake tomography from the trench to the magmatic arc our velocity model illuminates the main features within the subduction zone we interpret an east dipping high p wave velocity anomaly 6 9 km s as the subducting oceanic crust and a low p wave velocity we assess the role played by physical heterogeneity in governing megathrust behaviour greatest slip during the maule earthquake occurred in areas of moderate p wave velocity 6 5 7 5 km s where the interface is structurally more uniform at shallow depths high fluid pressure likely influenced the up dip limit of seismic activity the high velocity bodies lie above portions of the plate interface where there was reduced coseismic slip and minimal postseismic activity the northern velocity anomaly may have acted as a structural discontinuity within the forearc influencing the pronounced crustal seismicity in the pichilemu region our work provides evidence for how the ancient geological structure of the forearc may influence the seismic behaviour of subduction megathrusts

fluid overpressure in subduction plate boundary caused by mantle derived fluids abstract subduction plate boundaries are commonly weak owing to fluid overpressure the generation of fluid overpressure has been invoked for compaction disequilibrium and mineral dehydration in subducting sediments and altered oceanic crust the subduction melange in the shimanto accretionary complex southwest japan preserves the quartz calcite filled shear veins and sigmoidal extension veins formed under fluid overpressure near the downdip limit of the thermally controlled seismogenic zone the shear veins record the repeated low angle brittle thrusting under fluid overpressure while the extension veins constitute the riedel shear zones developed during subduction under vertical maximum principle stress to examine the origin of overpressured fluids we conducted fluid inclusion and noble gas analyses on the shear and extension veins the result of fluid inclusion analysis shows various fluid pressures between lithostatic to hydrostatic pressures during the vein formation which were associated with warm fluid infiltration 3he 4he values of shear veins and extension veins range 1 6 2 5 ra and 1 6 2 3 ra respectively indicating the presence of mantle helium 40ar 36ar values and 84kr 36ar and 130xe 36ar ratios of the veins are similar to those of serpentinized mantle suggesting that mantle helium originated from serpentinized mantle because the mantle derived rocks such as peridotite and serpentinite are absent in the melange the results of noble gas analyses represent the infiltration of fluids from the serpentinized mantle into the melange shear zone our results show that an infiltration of fluids derived from serpentinized mantle contributed the fluid overpressure in the melange shear zone near the downdip limit of the seismogenic zone

coseismic slip and afterslip of the 2015 mw 8 3 illapel chile earthquake determined from continuous gps data we analyzed the coseismic and early postseismic deformation of the 2015 mw 8 3 illapel earthquake by inverting 13 continuous gps time series the seismic rupture concentrated in a shallow 20 km depth and 100 km long asperity which slipped up to 8 m releasing a seismic moment of 3 6 1021 nm mw 8 3 after 43 days postseismic afterslip encompassed the coseismic rupture afterslip concentrated in two main patches of 0 50 m between 20 and 40 km depth along the northern and southern ends of the rupture partially overlapping the coseismic slip afterslip and aftershocks confined to region of positive coulomb stress change promoted by the coseismic slip the early postseismic afterslip was accommodated 53 aseismically and 47 seismically by aftershocks the illapel earthquake rupture is confined by two low interseismic coupling zones which coincide with two major features of the subducting nazca plate the challenger fault zone and juan fernandez ridge

large trench parallel gravity variations predict seismogenic behavior in subduction zones we demonstrate that great earthquakes occur predominantly in regions with a strongly negative trench parallel gravity anomaly tpga whereas regions with strongly positive tpga are relatively aseismic these observations suggest that over time scales up to at least 1 million years spatial variations of seismogenic behavior within a given subduction zone are stationary and linked to the geological structure of the fore arc the correlations we observe are consistent with a model in which spatial variations in frictional properties on the plate interface control trench parellel variations in fore arc topography gravity and seismogenic behavior

the reflection seismic survey of project tipteq the inventory of the chilean subduction zone at 38 2 s summary we describe results of an active source seismology experiment across the chilean subduction zone at 38 2 s the seismic sections clearly show the subducted nazca plate with varying reflectivity below the coast the plate interface occurs at 25 km depth as the sharp lower boundary of a 2 5 km thick highly reflective region which we interpret as the subduction channel that is a zone of subducted material with a velocity gradient with respect to the upper and lower plate further downdip along the seismogenic coupling zone the reflectivity decreases in the area of the presumed 1960 valdivia hypocentre the plate interface itself can be traced further down to depths of 50 60 km below the central valley we observe strong reflectivity at the plate interface as well as in the continental mantle wedge the sections also show a segmented forearc crust in the overriding south american plate major features in the accretionary wedge such as the lanalhue fault zone can be identified at the eastern end of the profile a bright west dipping reflector lies perpendicular to the plate interface and may be linked to the volcanic arc

mechanical properties and processes of deformation in shallow sedimentary rocks from subduction zones an experimental study to better constrain the mechanical behavior of sediments accreted to accretionary prism we conducted triaxial mechanical tests on natural samples from the miura boso paleo accretionary prism japan in drained conditions with confining pressures up to 200 mpa as well as postexperiments p wave velocity vp measurements during experiments deformation is principally noncoaxial and accommodated by two successive modes of deformation both associated with strain hardening and velocity strengthening behavior 1 compaction assisted shearing distributed in a several mm wide shear zone and 2 faulting localized within a few tens of m wide dilatant fault zone deformation is also associated with 1 a decrease in young s modulus all over the tests 2 anomalously low vp in the deformed samples compared to their porosity and 3 an increase in sensitivity of vp to effective pressure we interpret this evolution of the poroelastic properties of the material as reflecting the progressive breakage of intergrain cement and the formation of microcracks along with macroscopic deformation when applied to natural conditions these results suggest that the deformation style localized versus distributed of shallow z a few km sediments is mainly controlled by the variations in stress strain rate during the seismic cycle and is therefore independent of the porosity of sediments finally we show that the effect of strain through cement breakage and microcracks formation may lower vp for effective pressure up to 40 mpa as a consequence the low vp anomalies observed in nankai accretionary prisms by seismic imaging between 2 and 4 km depth could reflect sediment deformation rather than porosity anomalies

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

updip limit of the seismogenic zone beneath the accretionary prism of southwest japan an effect of diagenetic to low grade metamorphic processes and increasing effective stress off southwest japan the seaward limit of coseismic displacement or updip limit of the seismogenic zone of the 1946 mw 8 3 thrust earthquake reaches to 4 km depth and 40 km landward of the trench this limit coincides with the estimated location of the 150 c isotherm and has been linked to changes in physical properties associated with the smectite to illite clay mineral transition here we show that this limit correlates with a suite of diagenetic to low grade metamorphic processes characterized by 1 declining fluid production and decreasing fluid pressure ratio and 2 active clay carbonate and zeolite cementation and the transition to pressure solution and quartz cementation these diagenetic to low grade metamorphic changes cause the onset of velocity weakening during thrust faulting an increase in effective stress and strengthening of the hanging wall which together combine to produce recordable earthquakes

from geodetic imaging of seismic and aseismic fault slip to dynamic modeling of the seismic cycle understanding the partitioning of seismic and aseismic fault slip is central to seismotectonics as it ultimately determines the seismic potential of faults thanks to advances in tectonic geodesy it is now possible to develop kinematic models of the spatiotemporal evolution of slip over the seismic cycle and to determine the budget of seismic and aseismic slip studies of subduction zones and continental faults have shown that aseismic creep is common and sometimes prevalent within the seismogenic depth range interseismic coupling is generally observed to be spatially heterogeneous defining locked patches of stress accumulation to be released in future earthquakes or aseismic transients surrounded by creeping areas clay rich tectonites high temperature and elevated pore fluid pressure seem to be key factors promoting aseismic creep the generally logarithmic time evolution of afterslip is a distinctive feature of creeping faults that suggests a logarithmic dependency of fault friction on slip rate

the accretion of foreland basin sediments during early stages of continental collision in the european alps and similarities to accretionary wedge tectonics we present structural observations from foreland basin sediments that were incorporated into the orogenic wedge of the central european alps during early stages of continental collision our analysis focuses on the prograde evolution and considers the full history of the sediments ranging from their deposition in the basin to deep burial and metamorphism at temperatures of 320 c the tectonic evolution is matched with constraints on the diagenetic alteration of the sediments for this purpose we calculate the temperatures and depths of sediment compaction and illitization as well as the associated fluid liberation the data set highlights that the tectonic incorporation of the sediments into the orogenic wedge was strongly controlled by their diagenetic state earliest deformation took place during imbrication and frontal accretion of unconsolidated and fluid saturated sediments ductile folding of the sediments occurred already at this stage and was assisted by particulate flow with the progressive consolidation of the sediments the elastic strength increased which resulted in an overall embrittlement this rheological change is recorded by the onset of out of sequence thrusting brittle faulting and the formation of massive quartz calcite veins which took place in the approximate temperature range of the seismogenic zone i e 150 350 c moreover widespread pressure solution resulted in the formation of a penetrative cleavage and records slow but long lasting deformation at low background strain rates in summary the prograde tectonic evolution of the frontal alpine wedge exhibits many similarities with the structural and mechanical evolution of accretionary wedges at active subduction zones

exposed plate interface in the european alps reveals fabric styles and gradients related to an ancient seismogenic coupling zone 1 we present observations from a continuous exposure of an ancient plate interface in the depth range of its former seismogenic zone in the central alps of europe related to late cretaceous early tertiary subduction and accretion of the south penninic lower plate underneath the adriatic upper plate the material forming the exposed plate interface zone has experienced flow and fracturing over an extended period of time followed by syncollisional exhumation thus reflecting a multistage evolution fabric formation and metamorphism however chiefly record the deformation conditions of the precollisional setting along the plate interface we identify an unstable slip domain from pseudotachylytes occurring in the temperature range between 200 and 300 c this zone coincides with a domain of intense veining in the subduction melange with mineral growth into open cavities indicating fast possibly seismic rupture evidence for transient near lithostatic fluid pressure as well as brittle fractures competing with mylonitic shear zones continues into the region below the occurrence of pseudotachylytes possibly reflecting a zone of conditionally stable slip the zone above the unstable slip area is devoid of veins but displays ample evidence of fluid assisted processes similar to the deeper zone solution precipitation creep and dehydration reactions in the melange matrix hydration and sealing of the base of the upper plate seismic rupture here is possibly expressed by ubiquitous localized deformation zones we hypothesize that trenchward sealing of parts of the plate interface as well as reaction enhanced destruction of upper plate permeability is an important component localizing the unstable slip zone this relation may result from the competition of the pervasive presumably interseismic pressure solution creep destroying permeability and building elevated fluid pressure until the strength threshold is reached with seismic failure

locking of the chile subduction zone controlled by fluid pressure before the 2010 earthquake large subduction zone earthquakes are thought to occur where the down going and overriding tectonic plates are strongly locked analysis of geodetic and seismic data collected in the decade before the 2010 chile earthquake shows that variations in pore fluid pressure correlate with the degree of plate interface locking and may therefore control earthquake rupture

months long thousand kilometre scale wobbling before great subduction earthquakes megathrust earthquakes are responsible for some of the most devastating natural disasters1 to better understand the physical mechanisms of earthquake generation subduction zones worldwide are continuously monitored with geophysical instrumentation one key strategy is to install stations that record signals from global navigation satellite systems2 3 gnss enabling us to track the non steady surface motion of the subducting and overriding plates before during and after the largest events4 6 here we use a recently developed trajectory modelling approach7 that is designed to isolate secular tectonic motions from the daily gnss time series to show that the 2010 maule chile moment magnitude 8 8 and 2011 tohoku oki japan moment magnitude 9 0 earthquakes were preceded by reversals of 4 8 millimetres in surface displacement that lasted several months and spanned thousands of kilometres modelling of the surface displacement reversal that occurred before the tohoku oki earthquake suggests an initial slow slip followed by a sudden pulldown of the philippine sea slab so rapid that it caused a viscoelastic rebound across the whole of japan therefore to understand better when large earthquakes are imminent we must consider not only the evolution of plate interface frictional processes but also the dynamic boundary conditions from deeper subduction processes such as sudden densification of metastable slab

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

background seismicity rate at subduction zones linked to slab bending related hydration tectonic properties strongly control variations in seismicity among subduction zones in particular fluid distribution in subduction zones influences earthquake occurrence and it varies among subduction zones due to variations in fluid sources such as hydrated oceanic plates however the relationship between variations in fluid distribution and variations in seismicity among subduction zones is unclear here we divide earth s subduction zones into 111 regions and estimate background seismicity rates using the epidemic type aftershock sequence model we demonstrate that background seismicity rate correlates to the amount of bending of the incoming oceanic plate which in turn is related to the hydration of oceanic plates via slab bending related faults regions with large bending may have high seismicity rates because a strongly hydrated oceanic plate causes high pore fluid pressure and reduces the strength of the plate interface we suggest that variations in fluid distribution can also cause variations in seismicity in subduction zones

from the seismic cycle to long term deformation linking seismic coupling and quaternary coastal geomorphology along the andean megathrust measurement of interseismic strain along subduction zones reveals the location of both locked asperities which might rupture during megathrust earthquakes and creeping zones which tend to arrest such seismic ruptures the heterogeneous pattern of interseismic coupling presumably relates to spatial variations of frictional properties along the subduction interface and may also show up in the forearc morphology to investigate this hypothesis we compiled information on the extent of earthquake ruptures for the last 500 years and uplift rates derived from dated marine terraces along the south american coastline from central peru to southern chile we additionally calculated a new interseismic coupling model for that same area based on a compilation of gps data we show that the coastline geometry characterized by the distance between the coast and the trench the latitudinal variations of long term uplift rates and the spatial pattern of interseismic coupling are correlated zones of faster and long term permanent coastal uplift evidenced by uplifted marine terraces coincide with peninsulas and also with areas of creep on the megathrust where slip is mostly aseismic and tend to arrest seismic ruptures we conclude that spatial variations of frictional properties along the megathrust dictate the tectono geomorphological evolution of the coastal zone and the extent of seismic ruptures along strike

aftershocks driven by afterslip and fluid pressure sweeping through a fault fracture mesh a variety of physical mechanisms are thought to be responsible for the triggering and spatiotemporal evolution of aftershocks here we analyze a vigorous aftershock sequence and postseismic geodetic strain that occurred in the yuha desert following the 2010 m w 7 2 el mayor cucapah earthquake about 155 000 detected aftershocks occurred in a network of orthogonal faults and exhibit features of two distinct mechanisms for aftershock triggering the earliest aftershocks were likely driven by afterslip that spread away from the main shock with the logarithm of time a later pulse of aftershocks swept again across the yuha desert with square root time dependence and swarm like behavior together with local geological evidence for hydrothermalism these features suggest that the events were driven by fluid diffusion the observations illustrate how multiple driving mechanisms and the underlying fault structure jointly control the evolution of an aftershock sequence

probing the transition between seismically coupled and decoupled segments along an ancient subduction interface the transition zone at the downdip end of seismic coupling along subduction interfaces is often the site of megathrust earthquake nucleation and concentrated postseismic afterslip as well as the focus site of episodic tremor and slip features exhumed remnants of the former alpine subduction zone found in the swiss alps allow analyzing fluid and deformation processes near the transition zone region 30 40 km paleodepth the dent blanche thrust dbt is a lower blueschist facies shear zone interpreted as a fossilized subduction interface where granitic mylonites overlie a metamorphosed accretionary wedge we report field observations from the dbt region where multiple several tens of meters thick foliated cataclastic networks are interlayered within the basal dbt mylonites petrological results and microstructural observations indicate that the various cataclasis events took place at near peak metamorphic conditions 400 500 c 1 1 1 3 gpa during subduction of the tethyan seafloor in eocene times 42 48 ma some of these networks exhibit mutual crosscutting relationships between mylonites foliated cataclasites and vein systems indicating mutual overprinting between brittle deformation and ductile creep whole rock chemical compositions in situ 40ar 39ar age data of recrystallized phengite and sr isotopic signatures reveal that dbt rocks also underwent multiple hydrofracturing and metasomatic events via the infiltration of fluids mainly derived from the oceanic metasediments underneath the dbt from the rock fabrics we infer strain rate fluctuations of several orders of magnitude beyond subduction strain rates 10 12 s 1 accompanied by fluctuation of supralithostatic and quasi lithostatic fluid pressures 1 0 95 dbt brittle plastic deformation switches highlight the diversity of deformation processes and fluid rock interactions in the transition zone region of the subduction interface

the updip and downdip limits to great subduction earthquakes thermal and structural models of cascadia south alaska sw japan and chile this study examines thermal and structural controls of the updip and downdip rupture limits of great subduction thrust earthquakes data on past great earthquake seismic limits have been compiled for four continental subduction zones cascadia sw japan south alaska and chile these limits have then been compared to the predictions of several models for what constrains great earthquake rupture temperatures on the subduction thrusts have been estimated by finite element numerical models the landward limits of the observed updip aseismic zones correspond to the position where the thrust temperature reaches about 100 c that is depths of about 2 to 10 km for the subduction zones studied this temperature agrees with the dehydration of stable sliding smectite clays to illite chlorite the temperatures in this region are controlled mainly by the thickness of sediment on the incoming crust and by the crustal age and thus heat flow the downdip limits correspond to the depth on the thrust where either 1 the temperature reaches about 350 c which corresponds to thermally activated stable sliding behavior for crustal rocks with a transition to 450 c or 2 about 40 km depth if 350 c is reached at greater depth depths of about 40 km approximately correspond to the intersection of the thrust with the continental forearc moho and this downdip limit may be a consequence of stable sliding serpentinite or talc and other hydrated forearc mantle rocks the primary temperature controls on the downdip region are the age of the subducting oceanic plate and the thrust dip profile secondary control comes from the thickness of incoming sediment the convergence rate and the radioactive heat generation in the overlying forearc the 100 c updip limit occurs near the trench for young subducting plates with a thick sediment section such as cascadia 6 8 ma and up to 80 km landward for older oceanic crust such as south alaska 50 ma the 350 c downdip thermal limit is applicable for young oceanic plates e g cascadia and nankai whereas the forearc mantle limit applies for older plates e g south alaska and chile except near the chile rise for the margins studied that have experienced great earthquakes there is generally good agreement between the postulated thermal and moho limits and the rupture or seismogenic zone as defined by the distribution of aftershocks and by waveform tsunami and dislocation modeling the downdip limit of the interseismic locked zone from dislocation modeling is also in agreement with these limits

a secondary zone of uplift due to megathrust earthquakes the 1960 m9 5 valdivia and 1964 m9 2 alaska earthquakes caused a decimeters high secondary zone of uplift a few hundred kilometers landward of the trench we analyze gps data from the 2010 m8 8 maule and 2011 m9 0 tohoku oki earthquakes to reveal the persistent existence of a secondary zone of uplift due to great earthquakes at the megathrust interface this uplift varies in magnitude and location but consistently occurs at a few hundred kilometers landward from the trench and is likely mainly coseismic in nature this secondary zone of uplift is systematically predicted by our 2d visco elasto plastic seismo thermo mechanical numerical simulations which model both geodynamic and seismic cycle timescales through testing hypotheses in both simple and realistic setups we propose that a superposition of two physical mechanisms could be responsible for this phenomenon first a wavelength is introduced through elastic buckling of a visco elastically layered fore arc that is horizontally compressed in the interseismic period the consequent secondary zone of interseismic subsidence is elastically rebound during the earthquake into a secondary zone of relative uplift second absolute and broader uplift is ensured through a mass conservation driven return flow following accelerated slab penetration due to the megathrust earthquake the dip and width of the seismogenic zone and resulting deep coseismic slip seem to have the largest affect on location and amplitude of the secondary zone of uplift these results imply that subduction and mantle flow do not occur at constant rates but are rather modulated by earthquakes this suggests a link between deep mantle and shallow surface displacements even at time scales of minutes

electrical resistivity imaging of the inter plate coupling transition at the hikurangi subduction margin new zealand abstract inter plate coupling on the hikurangi subduction margin along the east coast of new zealand s north island changes from weakly coupled in the north to locked in the south 3 d inverse modeling of magnetotelluric mt data across the coupling transition shows that the electrical resistivity structure is correlated with the areal strain rate which provides a measure of plate coupling the correlation between strain rate and resistivity is seen parallel to the strike and dip directions of the subduction in the region where the strain is extensional the upper plate is more conductive than in the south where contraction is occurring and the plates are locked the increased mid crustal resistivity in the south can be interpreted to be a consequence of reduced fluid interconnectivity due to contraction or reduced fluid content due to decreased upward transport from sources beneath the subduction interface the increased mid crustal conductivity in the extensional area is interpreted to be a consequence of fluid released by subducted sediment that are also the cause of the extension seismicity in the upper 5 km of the subducting plate shows similar changes with a greater concentration of near interface seismicity beneath the conductive extensional region we interpret the concentration of seismicity below the subduction interface in the extensional region to show fluid sourced from dehydration reactions within the subducting plate or from the de watering of subducted sediments rising into the upper plate and decreasing the resistivity of the middle crust decreased near interface seismicity beneath the contractional region can be interpreted to be a consequence of decreased upper plate permeability preventing upward fluid escape or reduced lower plate fluid availability

contrasting amount of fluids along the megathrust ruptured by the 2010 maule earthquake as revealed by a combined analysis of aftershocks and afterslip abstract we present a novel approach combining time variable computations of b value and afterslip to study the postseismic activity following the mw 8 8 maule 2010 earthquake we subdivided the first 392 days after the mainshock into overlapping windows for which we compared maps of b value computed from neic seismicity and afterslip computed from continuous gps stations the correlation between both parameters is weak during the first 2 months when the aftershocks magnitude of completeness decreases and the number of gps stations increased after this early stage a correlation between both parameters emerges we interpret this correlated spatiotemporal pattern combining factors proposed to control each parameter separately this exercise suggests a segmentation of the maule megathrust the northern segment is characterized by an increase of afterslip and b value during the early postseismic phase and then a simultaneous decrease of both parameters which we interpret as the effect of an ingression of fluids into the megathrust and its subsequent consumption during fault healing in contrast the southern segment is characterized by a central region with minimum afterslip and low b value surrounded by areas that experience mostly seismic afterslip as a consequence of large static stress loaded by the mainshock suggesting a drier and stronger megathrust where healing was active earlier interpreted along with features of the pre and coseismic phases our results allow us to propose the existence of two contrasting types of seismic asperities classical strong stick slip patches that we link with dry regions of the megathrust versus weak wet and conditionally stable frictional patches that could have a range of seismogenic behaviors from creeping and or locking during the interseismic period largely contributing with coseismic slip and concentrating afterslip at their borders the application of our novel method to other great earthquakes could reveal whether this is a common or anomalous feature of megathrusts

ductile creep compaction and rate and state dependent friction within major fault zones the shear traction on major strike slip faults during earthquakes is much lower than that expected on a frictionally sliding surface in equilibrium with hydrostatic pressure the low shear traction is explained if the fluid pressure at the time of the earthquake is much greater than hydrostatic pressure ductile creep within mostly sealed fault zones compacts the matrix and thus increases fluid pressure between earthquakes frictional dilatancy during earthquakes decreases fluid pressure below hydrostatic and over the earthquake cycle the fault zone is in long term equilibrium with the country rock this ductile mechanism is formally unified with rate and state theory for time dependent friction when the difference between a critical porosity where the rock loses all strength and the actual porosity of cracks is used as a state variable this choice is justified by percolation theory of mostly broken lattices time dependent behavior associated with changes in normal traction in the laboratory is explained by the formalism instability earthquakes sometimes occurs in the numerical experiments however fairly small amounts of frictional dilatancy during initial frictional creep decrease fluid pressure and preclude unstable sliding two coupled mechanisms for producing dilatancy on faults once an instability is well underway are evident 1 expansion of pore fluids associated with frictional heating increases fluid pressure offsetting the effects of increased pore volume during earthquakes there is some tendency for pore volume increase to balance fluid expansion so that fluid pressure stays relatively constant 2 production of isolated voids that do not immediately decrease fluid pressure throughout the fault zone during earthquakes can occur to the extent that the fault zone is not significantly strengthened although the extent of both processes is constrained by energy considerations the variation of fluid pressure during earthquakes is not yet well enough understood to predict stress drop from observable material properties

detection of earthquake swarms at subduction zones globally insights into tectonic controls on swarm activity earthquake swarms are characterized by an increase in seismicity rate that lacks a distinguished mainshock and does not obey omori s law at subduction zones they are thought to be related to slow slip events sses on the plate interface earthquake swarms in subduction zones can therefore be used as potential indicators of slow slip events however the global distribution of earthquake swarms at subduction zones remains unclear here we present a method for detecting such earthquake sequences using the space time epidemic type aftershock sequence etas model we applied this method to seismicity m 4 5 recorded in the anss catalog at subduction zones during the period 1995 2009 we detected 453 swarms which is about 6 7 times the number observed in a previous catalog foreshocks of some large earthquakes are also detected as earthquake swarms in some subduction zones such as at ibaraki oki japan swarm like foreshocks and ordinary swarms repeatedly occur at the same location given that both foreshocks and swarms are related to sses on the plate interface these regions may have experienced recurring sses we then compare the swarm activity and tectonic properties of subduction zones finding that swarm activity is positively correlated with curvature of the incoming plate before subduction this result implies that swarm activity is controlled either by hydration of the incoming plate or by heterogeneity on the plate interface due to fracturing related to slab bending

seamount subduction at the north ecuadorian convergent margin effects on structures inter seismic coupling and seismogenesis at the north ecuadorian convergent margin 1 s 1 5 n the subduction of the rough nazca oceanic plate leads to tectonic erosion of the upper plate and complex seismogenic behavior of the megathrust we used three selected pre stack depth migrated multi channel seismic reflection lines collected during the sisteur cruise to investigate the margin structure and decipher the impact of the subducted atacames seamounts on tectonic erosion interseismic coupling and seismogenesis in the region of the 1942 mw7 8 earthquake this dataset highlights a subducted 30 40 km 30 40 km double peak seamount that belongs to the atacames seamount chain and that is associated with a deep morphologic re entrant containing mass transport deposits the seamount subduction uplifted the margin basement by 1 6 km and pervasively broke the margin by deep and intense reverse faulting ahead of the seamount a process that is likely to weaken considerably the margin in the seamount wake the basement reverse fault system rotated counter clockwise this faulted basement is overlain with slope sediment sliding along listric normal faults that sole out onto the bsr this superposition of deep tectonic contraction within the basement and shallow gravitational extension deformation within the sediment highlights the key role of gas hydrate on outer slope erosion in addition to long term regional basal erosion the margin basement has thinned locally by an extra 0 8 1 km in response to the subduction of the atacames seamount chain and hydrofracturing by overpressured fluids at the margin toe this pervasively and deeply fractured margin segment is associated with a seismically quiet and gps modeled low interseismic coupling corridor that terminates downdip near the 1942 epicenter and locked zone we suggest that the deeply buried double peak atacames seamount triggered the 1942 earthquake ahead of its leading flank this result supports previous studies proposing that subducted seamounts provide unfavorable conditions for locking the updip segment of the plate boundary limiting the updip extent of seismogenic zones but may favor large subduction earthquakes at greater depths