a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

modeling of slow slip events along the deep subduction zone in the kii peninsula and tokai regions southwest japan 1 in the subduction zone of southwest japan short term slow slip events sses occur with low frequency tremors lfts at intervals of several months recently lfts have been located with high resolution and their activities have been examined in detail by setting the generation zones of sses such that these zones contain the lft hypocenters we simulate sses on a 3d plate interface beneath the kii peninsula and tokai regions by using a rate and state dependent friction law with a small cut off velocity for the evolution effect our numerical results show that recurrence intervals of sses in the southern and central kii peninsula in the northern kii peninsula and in the tokai region are 2 5 3 0 4 8 5 6 and 3 5 4 5 months respectively which are consistent with observed sse activity our simulation also produces a multisegment event that propagates from the kii to tokai segments at a speed of 10 km day which is consistent with observations the results suggest that generation zones of lfts coincide with sse regions and that these two events are different manifestations of the same slip process along the subduction zone we also perform 3d modeling of faster events accompanied by short term sses by considering local circular patches with a smaller critical displacement surrounded by sse zones with a larger critical displacement local circular patches are set at the observed lft locations the simulation reproduces fast events that propagate at a speed of 100 200 km day during a single sse event

slip behavior transitions of a heterogeneous linear fault geological faults have frictional heterogeneity here we investigate the slip behavior of such heterogeneous faults in the simplest situation simulating anti plane shear slip along an infinite linear fault in a 2d elastic model space subjected to constant loading by external stresses characterized by stiffness and plate motion velocity the fault is discretized into many sub faults each of which has either a velocity weakening vw or velocity strengthening vs friction law we vary the proportion of the fault that is vw revealing several different regimes of slip behavior the first regime boundary where stick slip behavior is initiated is located at the proportion of vw zones such that each vw zone reaches its nucleation size the other boundary is located where the spatially averaged a b value of the rate and state friction law is close to zero below this density the vw zone slips seismically whereas the vs zone shows afterslip in contrast above this density the entire fault slips simultaneously at the seismic slip velocity we observe transitional behavior at the second boundary where relatively slower deformation dominates we also explore the slip behavior of faults using cantor set distributions of frictional parameters we propose that frictional heterogeneity on the fault may explain not only the diversity of seismic phenomena but also the observed scaling of frictional parameters such as slip weakening distance or the fracture energy of ordinary earthquakes

role of fault gouge dilatancy on aseismic deformation transients 1 in the vicinity of episodic aseismic transients in several subduction zones the presence of interstitial fluids and near lithostatic pore pressure has been proposed to interpret seismic observations of high p to s wave speed ratio and high poisson s ratio under such conditions fault stabilization by dilatancy induced suction during increased shear strain rates becomes very efficient we analyze the frictional and hydraulic conditions for spontaneous transients on a fluid infiltrated fault including dilatancy and pore compaction in the framework of rate and state friction with a membrane diffusion approximation in both a simplified spectral model and a 2 d cascadia like subduction fault model the fault response is mainly controlled by three nondimensional parameters 1 w h the along dip width of the high pore pressure velocity weakening fault relative to a characteristic nucleation size 2 a drainage parameter u the relative time scales for fluid diffusion and friction evolution and 3 a dilatancy parameter e the relative contributions to stress drop from dilatancy and friction evolution the incorporation of dilatancy enables aseismic transients at much larger values of w h than is possible under conditions of constant pore pressure an analytic estimate of the maximum slip velocity as a function of w h e and u is derived and agrees reasonably well with the simulation results the dependence of the properties of modeled transients on the drainage parameter u is similar to that on the dilatancy parameter e for u e less than 1 maximum velocity decreases while recurrence period remains relatively constant for u e greater than 1 maximum velocity approaches the steady state velocity and recurrence period approaches the period at neutral stability in the subduction fault model using gabbro gouge friction properties the slip per episode and the recurrence period increase with w h generally following the trend defined without dilatancy the maximum velocity with dilatancy can be several orders of magnitude smaller than that without in particular for larger values of e and values of w h near the no dilatancy stability limit

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

earthquake cycles in a model of interacting fault patches complex behavior at transition from seismic to aseismic slip numerical simulations of complex earthquake cycles are conducted using a model with two patches asperities on a fault where friction obeys a rate and state dependent law the patches are represented by regions of steady state velocity weakening friction and are in contact with each other or are separated by a region of steady state velocity strengthening friction simulated earthquake cycles are examined by changing the characteristic slip distance of friction in one patch while that in the other patch is maintained at a constant as the characteristic slip distance in a patch increases the slip at the patch tends to be aseismic and rupture tends to be delayed as compared to rupture at the other patch or arrested due to an increase in fracture energy as a result the slip pattern changes in a complicated manner with the change of the parameter a complex multiperiodic or aperiodic slip pattern occurs in the simulation and this pattern tends to occur near the boundaries between regions of different slip behavior characteristics such as the boundary between seismic and aseismic slip in the patch with a larger characteristic slip distance iteration maps of the recurrence intervals of simulated earthquakes for an aperiodic sequence are sometimes expressed by simple curves suggesting that the simulated earthquake cycles exhibit deterministic chaos in the two patch models of the present study an aperiodic slip pattern is observed for narrower parameter ranges than in a model of a two degree of freedom spring block system which is usually regarded as a simplified model of a fault with two patches online material simulated histories of moment release rate and recurrence interval of simulated slip events in the two patches and seismic coupling coefficients

anisotropic viscoplasticity explains slow slip m 0 t scaling at convergent plate margins abstract in this study we quantify the mechanisms that govern two related observations with regard to deep 15 50 km subduction zone aseismic slow slip events sses i the linear scaling relationship between seismic moments m0 and event durations t and ii the direction dependent slow slip rupture speeds geological observations suggest that deep subduction slow slip shear zones are anisotropic and viscoplastic the anisotropy is due to the presence of dip parallel mafic lineaments created by seamount subduction whereas the viscoplasticity is due to deformation of mixed brittle mafic and ductile felsic materials we postulate that a dip parallel slip direction mafic lineament in an overall felsic slow slip shear zone acts as a stress guide which localizes initial slow slip rupture in the dip direction subsequent stress concentration along the dip parallel edges of the early ruptured lineament leads to along strike rupture with the rupture front propagating through the felsic shear zone the second phase slip area expansion maintains a constant dip parallel rupture zone length inherited from the length of the early ruptured mafic lineament by combining an energy balance equation with a two phase rupture model outlined above we obtain the first analytical expression of the observed linear scaling law in the form of m0 c0t where c 0 4 1 z g 2 l 2 s d gh z e cos v fw 2 l z s 2 d 2 gh 2 4 1 g l z zlg v fw v a 2 the observed value of this empirical constant is between 1011 5 and 1013 5 j s in the above expression l h z g e s and d are length depth thickness dip angle shear rigidity effective viscosity and effective coefficients of static and dynamic friction of the slow slip shear zone 1 is surface energy density of the initially ruptured mafic lineament is overriding plate density vfw and va are subducting plate and slow slip velocities and g is surface gravity our model based on the assumed shear zone anisotropy successfully predicts fast 100 km h dip parallel rupture along high viscosity 1020 pa s mafic lineaments and slow 2 10 km day strike parallel rupture through low viscosity 1017 pa s felsic materials during a deep subduction slow slip event

a possible model for large preseismic slip on a deeper extension of a seismic rupture plane abstract i develop a numerical model for preseismic slip and episodic aseismic slip events slow earthquakes on a deeper extension of a seismogenic plate interface using a rate and state dependent friction law the deep preseismic slip and episodic slow slip were indicated by models based on geodetic observations though they cannot be explained by common rate and state dependent laws i investigate whether this incongruity can be removed by including use of additional known constraints on the frictional property the steady state friction on a model fault is taken to be velocity weakening at low velocities and velocity strengthening at high velocities the transition velocity from velocity weakening friction to velocity strengthening is assumed to be the seismic slip velocity at shallow seismic depths and decreases with depth at deeper parts simulation results for a 2d model of interplate earthquakes at a subduction zone are as follows 1 during an interseismic period between successive large earthquakes at shallow seismogenic depths some episodic aseismic slip events with durations of a few years occur on the plate interface just below the seismogenic depths 2 preseismic slip occurs at nearly the same location where the episodic aseismic slip events occur these may explain some characteristics of observed preseismic slip of the 1944 tonankai earthquake m 7 9 along the nankai trough central japan and episodic aseismic slip events in the same area

modelling of short interval silent slip events in deeper subduction interfaces considering the frictional properties at the unstable stable transition regime summary recent high resolution observations of crustal movements have revealed silent slip events sses with propagation velocities of around 10 15 km d 1 and with intervals of 3 14 months along the deeper parts of the cascadia and nankai subduction zones this study develops 2 d and 3 d models of these short interval sses considering the frictional behaviour that was confirmed experimentally by shimamoto for the unstable stable transition regime to represent this frictional behaviour a small cut off velocity to an evolution effect is introduced in a rate and state dependent friction law when the cut off velocity to the evolution effect is significantly smaller than that to a direct effect steady state friction exhibits velocity weakening at low slip velocities and velocity strengthening at high slip velocities at the deeper cascadia and nankai subduction interfaces the pore pressure is inferred to be high because of the dehydration of materials in the descending plate under conditions where the pore fluid pressure is nearly equal to the lithostatic pressure and the critical weakening displacement is very small short interval sses with propagation velocities and slip velocities of 4 8 km d 1 and 2 4 10 7 m s 1 respectively can be reproduced the propagation velocity of short interval sses is in proportion to the slip velocity the results also show that during the nucleation process of large earthquakes the occurrence of short interval sses becomes irregular because of the accelerated slips that occur at the bottom of the seismogenic zone our results suggest that monitoring of short interval sses might be useful for forecasting the main earthquakes

complex evolution of transient slip derived from precise tremor locations in western shikoku japan transient slip events which occur more slowly than traditional earthquakes are increasingly being recognized as important components of strain release on faults and may substantially impact the earthquake cycle surface based geodetic instruments provide estimates of the overall slip distribution in larger transients but are unable to capture the detailed evolution of such slip either in time or in space accompanying some of these slip transients is a relatively weak extended duration seismic signal known as nonvolcanic tremor which has recently been shown to be generated by a sequence of shear failures occurring as part of the slip event by precisely locating the tremor we can track some features of slip evolution with unprecedented resolution here we analyze two weeklong episodes of tremor and slow slip in western shikoku japan we find that these slip transients do not evolve in a smooth and steady fashion but contain numerous subevents of smaller size and shorter duration in addition to along strike migration rates of 10 km d observed previously much faster migration also occurs usually in the slab dip direction at rates of 25 150 km h over distances of up to 20 km we observe such migration episodes in both the updip and downdip directions these episodes may be most common on certain portions of the plate boundary that generate strong tremor in intermittent bursts the surrounding regions of the fault may slip more continuously driving these stronger patches to repeated failures tremor activity has a strong tidal periodicity possibly reflecting the modulation of slow slip velocity by tidal stresses

rate weakening friction characterizes both slow sliding and catastrophic failure of landslides abstract catastrophic landslides cause billions of dollars in damages and claim thousands of lives annually whereas slow moving landslides with negligible inertia dominate sediment transport on many weathered hillslopes surprisingly both failure modes are displayed by nearby landslides and individual landslides in different years subjected to almost identical environmental conditions such observations have motivated the search for mechanisms that can cause slow moving landslides to transition via runaway acceleration to catastrophic failure a similarly diverse range of sliding behavior including earthquakes and slow slip events occurs along tectonic faults our understanding of these phenomena has benefitted from mechanical treatments that rely upon key ingredients that are notably absent from previous landslide descriptions here we describe landslide motion using a rate and state dependent frictional model that incorporates a nonlocal stress balance to account for the elastic response to gradients in slip our idealized one dimensional model reproduces both the displacement patterns observed in slow moving landslides and the acceleration toward failure exhibited by catastrophic events catastrophic failure occurs only when the slip surface is characterized by rate weakening friction and its lateral dimensions exceed a critical nucleation length h h that is shorter for higher effective stresses however landslides that are extensive enough to fall within this regime can nevertheless slide slowly for months or years before catastrophic failure our results suggest that the diversity of slip behavior observed during landslides can be described with a single model adapted from standard fault mechanics treatments

a microphysical interpretation of rate and state dependent friction for fault gouge the evolution of fault strength during the seismic cycle plays a key role in the mode of fault slip nature of earthquake stress drop and earthquake nucleation laboratory based rate and state dependent friction rsf laws can describe changes in fault strength during slip but the connections between fault strength and the mechanisms that dictate the mode of failure from aseismic creep to earthquake rupture remain poorly understood the empirical nature of rsf laws remains a drawback to their application in nature here we analyze an extensive data set of friction constitutive parameters with the goal of illuminating the microphysical processes controlling rsf we document robust relationships between 1 the initial value of sliding or kinetic friction 2 rsf parameters and 3 the time rates of frictional strengthening aging we derive a microphysical model based on asperity contact mechanics and show that these relationships are dictated by 1 an activation energy that controls the rate of asperity growth by plastic creep and 2 an inverse relationship between material hardness and the activation volume of plastic deformation collectively our results illuminate the physics expressed by the rsf parameters and which describe the absolute value of frictional strength and its dependence on time and slip rate moreover we demonstrate that seismogenic fault behavior may be dictated by the interplay between grain properties and ambient conditions controlling the local shear strength of grain scale asperity contacts

slow strain release along the eastern marmara region offshore istanbul in conjunction with enhanced local seismic moment release abstract we analyze a large transient strainmeter signal recorded at 62 5 m depth along the southern shore of the eastern sea of marmara region in northwestern turkey this region represents a passage of stress transfer from the izmit rupture to the marmara seismic gap the strain signal was recorded at the esenkoy site by one of the icdp gonaf international continental drilling programme geophysical observatory at the north anatolian fault strainmeters on the armutlu peninsula with a maximum amplitude of 5 microstrain and lasting about 50 days the onset of the strain signal coincided with the origin time of a mw 4 4 earthquake offshore yalova which occurred as part of a seismic sequence including eight mw 3 5 earthquakes the mw 4 4 event occurred at a distance of about 30 km from esenkoy on june 25th 2016 representing the largest earthquake in this region since 2008 before the event the maximum horizontal strain was subparallel to the regional maximum horizontal stress derived from stress inversion of local seismicity during the strain transient we observe a clockwise rotation in the local horizontal strain field of about 20 the strain signal does not correlate with known environmental parameters such as annual changes of sea level rainfall or temperature the strain signal could indicate local slow slip on the cinarcik fault and thus a transfer of stress to the eastern marmara seismic gap

the rupture extent of low frequency earthquakes near parkfield ca the low frequency earthquakes lfes that constitute tectonic tremor are often inferred to be slow to have durations of 0 2 to 0 5 s a factor of 10 to 100 longer than those of typical m w 1 2 earthquakes here we examine lfes near parkfield ca in order to assess several proposed explanations for lfes long durations we determine lfe rupture areas and location distributions using a new approach similar to directivity analysis where we examine how signals coming from various locations within lfes finite rupture extents create differences in the apparent source time functions recorded at various stations we use synthetic ruptures to determine how much the lfe signals recorded at each station would be modified by spatial variations of the source station travel time within the rupture area given various possible rupture diameters and then compare those synthetics with the data our synthetics show that the methodology can identify inter station variations created by heterogeneous slip distributions or complex rupture edges and thus lets us estimate lfe rupture extents for unilateral or bilateral ruptures to obtain robust estimates of the sources similarity across stations we stack signals from thousands of lfes using an empirical green s function approach to isolate the lfes apparent source time functions from the path effects our analysis of lfes in parkfield implies that lfes apparent source time functions are similar across stations at frequencies up to 8 to 16 hz depending on the family the inter station coherence observed at these relatively high frequencies or short wave lengths down to 0 2 to 0 5 km suggest that lfes in each of the 7 families examined occur on asperities they are clustered in patches with sub 1 km diameters the individual lfes rupture diameters are estimated to be smaller than 1 1 km for all families and smaller than 0 5 km and 1 km for the two shallowest families which were previously found to have 0 2 s durations coupling the diameters with the durations suggests that it is possible to model these m w 1 2 lfes with earthquake like rupture speeds around 70 of the shear wave speed however that rupture speed matches the data only at the edge of our uncertainty estimates for the family with highest coherence the data for that family are better matched if lfes have rupture velocities smaller than 40 of the shear wave speed or if lfes have different rupture dynamics they could have long rise times contain composite sub ruptures or have slip distributions that persist from event to event

quantitative measure of the variation in fault rheology due to fluid rock interactions we analyze friction data from two published suites of laboratory tests on granite in order to explore and quantify the effects of temperature t and pore water pressure pp on the sliding behavior of faults rate stepping sliding tests were performed on laboratory faults in granite containing gouge granite powder both dry at 23 to 845 c lockner et al 1986 and wet pp 100 mpa at 23 to 600 c blanpied et al 1991 1995 imposed slip velocities v ranged from 0 01 to 5 5 m s and effective normal stresses were near 400 mpa for dried granite at all temperatures and wet granite below 300 c the coefficient of friction shows low sensitivity to v t and pp for wet granite above 350 drops rapidly with increasing t and shows a strong positive rate dependence and protracted strength transients following steps in v presumably reflecting the activity of a water aided deformation process by inverting strength data from velocity stepping tests we determined values for parameters in three formulations of a rate and state dependent constitutive law one or two state variables were used to represent slip history effects each velocity step yielded an independent set of values for the nominal friction level five constitutive parameters transient parameters a b1 and b2 and characteristic displacements dc1 and dc2 and the velocity dependence of steady state friction ss ln v a b1 b2 below 250 data from dry and most wet tests are adequately modeled by using the slip law ruina 1983 and one state variable a 0 003 to 0 018 b 0 001 to 0 018 dc 1 to 20 m dried tests above 250 can also be fitted with one state variable in contrast wet tests above 350 require higher direct rate dependence a 0 03 to 0 12 plus a second state variable with large negative amplitude b2 0 03 to 0 14 and large characteristic displacement dc2 300 to 4000 m thus the parameters a b1 and b2 for wet granite show a pronounced change in their temperature dependence in the range 270 to 350 c which may reflect a change in underlying deformation mechanism we quantify the trends in parameter values from 25 to 600 c by piecewise linear regressions which provide a straightforward means to incorporate the full constitutive response of granite into numerical models of fault slip the modeling results suggest that the succeptibility for unstable stick slip sliding is maximized between 90 and 360 c in agreement with laboratory observations and consistent with the depth range of earthquakes on mature faults in the continental crust

fracture and weakening of jammed subduction shear zones leading to the generation of slow slip events geodetic data have revealed that parts of subduction interfaces creep steadily or transiently transient slow slip events sses are typically interpreted as aseismic frictional sliding however sses may also occur via mixed visco brittle deformation as observed in shear zones containing mixtures melange of strong fractured clasts embedded in a weak visco brittle matrix we test the hypothesis that creep in a subduction melange occurs through distributed matrix deformation where flow is intermittently impeded by load bearing clast networks jamming our numerical models demonstrate that bulk melange rheology can be dominated by the strong clasts in the absence of fracturing while at high driving stresses or low frictional strength clast fracturing redistributes deformation into the matrix leading to high bulk strain rates because melange stress is heterogeneous fracturing of clasts occurs throughout jammed melange when the driving stresses are only 20 of the clast yield strength the effective rheology of jammed melange can be characterised by a logarithmic dependence of stress on strain rate which is used to explore strain rate transients caused by temporal variation in clast friction clasts must weaken significantly 75 in order to increase strain rate by 8 spring block slider models with a more idealized visco brittle rheology also demonstrate that strain rate transients can be generated when rate and state friction is incorporated we outline a model where high bulk strain rates are generated when pervasive fracturing occurs but further slip is limited by viscous processes incorporating such viscous damping into models may widen the conditions under which sses can occur while preventing development of seismic slip

slip rate dependent friction as a universal mechanism for slow slip events a growing body of observations worldwide has documented fault slip transients that radiate little or no seismic energy the mechanisms that govern these slow slip events sses and their wide range of depths slip rates durations stress drops and recurrence intervals remain poorly known here we show that slow slip can be explained by a transition from rate weakening frictional sliding at low slip rates towards rate neutral or rate strengthening behaviour at higher slip rates as has been observed experimentally we use numerical simulations to illustrate that this rate dependent transition quantitatively explains the experimental data for natural fault rocks representative of materials in the source regions of sses with a standard constant parameter rate and state friction law sses arise only near the threshold for slip instability the inclusion of velocity dependent friction parameters substantially broadens the range of conditions for slow slip occurrence and produces a wide range of event characteristics which include stress drop duration and recurrence as observed in nature upscaled numerical simulations that incorporate parameters consistent with laboratory measurements can reproduce geodetic observations of repeating sses on tectonic faults we conclude that slip rate dependent friction explains the ubiquitous occurrence of sses in a broad range of geological environments a transition from rate weakening to rate strengthening frictional behaviour with increasing slip rate could explain the observed diversity of slow slip events on faults according to numerical simulations

long period seismicity in the shallow volcanic edifice formed from slow rupture earthquakes volcanic eruptions are often preceded by long period seismic events that were thought to be generated by the resonance of cracks filled with magmatic fluid analysis and modelling of long period seismicity at volcanoes in italy costa rica and peru shows that it could instead be caused by slow rupture along faults in the upper volcanic edifice

on the physical mechanism of silent slip events along the deeper part of the seismogenic zone 1 to investigate the mechanism of recently observed silent slip events we simulated earthquake preparation processes using the dieterich ruina rate and state dependent friction law to ensure realistic modeling of the unstable stable transition we considered small cut off velocity to an evolution effect in the friction law for the transition zone when the cut off velocity to the evolution effect is significantly smaller than that of a direct effect steady state friction behaves as velocity weakening at low slip velocity and velocity strengthening at high slip velocity this frictional behavior was experimentally and theoretically confirmed for the unstable stable transition zone the results of our numerical simulations show that silent slips of which velocity is higher than the velocity of relative plate motion eventually propagates horizontally along the unstable stable transition over a period of several years silent slip events can be interpreted as being caused by the transitional behavior of the fault constitutive law

earthquake nucleation on rate and state faults aging and slip laws we compare 2 d quasi static earthquake nucleation on rate and state faults under both aging and slip versions of the state evolution law for both versions mature nucleation zones exhibit 2 primary regimes of growth well above and slightly above steady state corresponding respectively to larger and smaller fault weakening rates well above steady state aging law nucleation takes the form of accelerating slip on a patch of fixed length this length is proportional to b 1 and independent of a where a and b are the constitutive parameters relating changes in slip speed and state to frictional strength under the slip law the nucleation zone is smaller and continually shrinks as slip accelerates the nucleation zone is guaranteed to remain well above steady state only for values of a b that are low by laboratory standards near steady state for both laws the nucleation zone expands the propagating front remains well above steady state giving rise to a simple expression for its effective fracture energy g c this fracture energy controls the propagation style for the aging law g c increases approximately as the square of the logarithm of the velocity jump this causes the nucleation zone to undergo quasi static crack like expansion to a size asymptotically proportional to b b a 2 for the slip law g c increases only as the logarithm of the velocity jump and crack like expansion is not an option instead the nucleation zone grows as an accelerating unidirectional slip pulse under both laws the nucleation front propagates at a velocity larger than the slip speed by roughly b divided by the logarithm of the velocity jump where is the effective elastic shear modulus for this prediction to be consistent with observed propagation speeds of slow slip events in subduction zones appears to require effective normal stresses as low as 1 mpa

tectonic tremor along the northern hikurangi margin new zealand between 2010 and 2015 we present the first comprehensive tectonic tremor catalog for the northern hikurangi margin obtained from the systematic analysis of data from the new zealand seismic network between 2010 and 2015 the recent densification of this array along the northern hikurangi margin has allowed for the detection and location of tectonic tremor associated with 20 out of 26 identified transients in the continuous gps record along the east coast of the raukumara peninsula eighteen of these transients have never been reported in the literature and are likely to be slow slip events with magnitudes smaller than those previously studied we also investigate the spatiotemporal relationships between shallow offshore slow slip tectonic tremor and earthquakes for the duration of the study period

influence of dilatancy on the frictional constitutive behavior of a saturated fault zone under a variety of drainage conditions we use numerical simulations to investigate how fault zone dilatancy and pore fluid decompression influence fault strength and friction constitutive behavior dilatant hardening can change the frictional response and the effective critical stiffness kcr which determines the transition from stable to unstable sliding in velocity weakening fault zones we study the frictional shear strength response to numerical velocity stepping experiments and show that when the duration of pore fluid decompression is long compared to the time necessary for frictional evolution as dictated by rate and state friction both the effective critical slip distance dc and the effective shear strength direct effect a are increased we investigate the role of fault zone permeability k dilatancy coefficient varepsilon and the magnitude of shearing velocity of the fault zone vlp and compare results using the dieterich and ruina state evolution laws over the range from k 10 15 to 10 21 m2 dc increases from 25 m to 2 mm and a increases from 0 15 to 5 mpa we vary varepsilon from 10 5 to 10 3 and the size of the velocity perturbation from 3x to 1000x and find large increases in the values of dc and a which may lead to inhibition of unstable sliding our results indicate that spatial variations with either depth or lateral extent in varepsilon and k could result in significant changes in the drainage state in fault zones such variation may lead to spatial variation of the nucleation and propagation of earthquakes based upon the drainage capabilities of the fault zone

change of apparent segmentation of the san andreas fault around parkfield from space geodetic observations across multiple periods sequences of earthquakes are commonly represented as a succession of periods of interseismic stress accumulation followed by coseismic and postseismic phases of stress release because the recurrence time of large earthquakes is often greater than the available span of space geodetic data it has been challenging to monitor the evolution of interseismic loading in its entire duration here we analyze large data sets of surface deformation at different key episodes around the cholame parkfield and creeping segments of the san andreas fault that show evidence of significant deceleration of fault slip during the interseismic period we compare the average fault slip rates before and after the 2004 mw6 parkfield earthquake in the 1986 2004 and 2006 2012 periods respectively avoiding 2 years of postseismic deformation after 2004 using a combination of gps data from the plate boundary observatory the southern california earthquake center crustal motion map and the bay area velocity unification networks and interferometric synthetic aperture radar from the advanced land observing satellite alos and envisat satellites we show that the area of coupling at the transition between the parkfield and cholame segments appears larger later in the interseismic period than it does earlier on while strong plate coupling is uniform across the parkfield and cholame segments in the 1986 2004 period creep occurs south of the 2004 epicenter after 2006 making segmentation of the san andreas fault south of parkfield more clearly apparent these observations indicate that analyses of surface deformation late in the earthquake cycle may overestimate the area of plate coupling a fault surface creeping much below plate rate may in some case be a region that does not promote earthquake nucleation but rather just be at a slower stage of its evolution our analysis also shows signs of large variation of slip velocity above and below plate rate in the creeping segment indicating that cycles of weakening and hardening can also be at play in dominantly aseismic areas

stress transfer and strain rate variations during the seismic cycle 1 the balance of forces implies stress transfers during the seismic cycle between the elastobrittle upper crust and the viscoelastic lower crust this could induce observable time variations of crustal straining in the interseismic period we simulate these variations using a one dimensional system of springs sliders and dashpot loaded by a constant force the seismogenic zone and the zone of afterslip below are modeled from rate and state friction the ductile deeper fault zone is modeled from a viscous slider with newtonian viscosity n the force per unit length f must exceed a critical value fc to overcome friction resistance of the fault system this simple system produces periodic earthquakes the recurrence period tcycle and the duration of the postseismic relaxation phase which is driven dominantly by afterslip then both scale linearly with n between two earthquakes interseismic strain buildup across the whole system is nonstationary with the convergence rates vi just after each earthquake being systematically higher than the value vf at the end of the interseismic period we show

laterally propagating slow slip events in a rate and state friction model with a velocity weakening to velocity strengthening transition we investigate the behavior of simulated slow slip events using a rate and state friction model that is steady state velocity weakening at low slip speeds but velocity strengthening at high slip speeds our simulations are on a one dimensional line fault but we modify the elastic interactions to mimic the elongate geometry frequently observed in slow slip events simulations exhibit a number of small events as well as periodic large events the large events propagate approximately steadily along strike and stress and slip rate decay gradually behind the propagating front their recurrence intervals can be determined by considering what is essentially an energy balance requirement for long distance propagation it is possible to choose the model parameters such that the simulated events have the stress drops slip velocities and propagation rates observed in cascadia

multi event simulations of slow slip events for a cascadia like subduction zone 1 we employ the earthquake simulator rsqsim which incorporates rate and state dependent friction to investigate characteristics of slow slip events sses along a cascadia like mega thrust the simulations consist of 100 000 sses with equivalent moment magnitudes mw4 0 7 0 the largest simulated sses mw6 4 7 0 have inter event times of 19 months durations of 10 40 days mean slips of 2 2 4 1 cm and along strike propagation speeds of 7 20 km day which are comparable to observations from cascadia the simulations show quiescence after mw 6 4 sses followed by a progressive increase in both the magnitude and frequency of sses prior to the next large event small sses below mw5 6 develop in an incoherent manner and have irregular geometries while larger sses show highly coherent growth of the slip region and spontaneous but transient event to event segmentation the change in event characteristics at mw5 6 corresponds to a break in the scaling of seismic moment with slip fault area and duration

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

diverse slow slip behavior at the hikurangi subduction margin new zealand 1 the installation of a continuous gps cgps network in new zealand since 2002 has enabled the discovery of 15 slow slip events at the hikurangi subduction margin our analysis and interpretation of the cgps data reveal a marked diversity in characteristics of slow slip events sses in the north island with durations varying from 6 days to 1 5 years equivalent moment release between mw 6 3 7 2 and recurrence intervals of repeating sses on the order of 2 years to more than 5 years the duration and magnitude characteristics of hikurangi sses appear to be related to the depth where they occur the deepest longest duration and largest sses occur at the southern hikurangi margin near the downdip limit of deep down to 40 km depth strong interseismic coupling the shallowest shortest duration smallest and most frequent sses occur at the northern and central hikurangi margin near the downdip limit of unusually shallow 10 15 km depth interseismic coupling the direction of slip on the interface in the hikurangi sses is consistent with slip partitioning at the hikurangi subduction margin we also show that moment accumulation rates on the interface for the time periods between sses are 40 higher than for the period of more than a decade averaging through the sses indicating that sses compose a major portion of the overall moment release budget of the hikurangi subduction interface

slow slip and tremor search at kilauea volcano hawaii 1 kilauea volcano hawaii has hosted a long series of slow slip events observed since the installation of the continuous gps network in 1996 kilauea s slow slip events are inferred to occur on the decollement fault at 8 km depth beneath its south flank with a location updip of the epicenters of large regular earthquakes fault slip typically lasts about two days and the events have magnitudes equivalent to mw 5 3 6 0 while slow slip events in subduction zones are commonly accompanied by tectonic tremor also called nonvolcanic tremor no tremor has yet been reported in association with kilauea s slow slip events instead there are swarms of small triggered earthquakes which is a characteristic only seen at select subduction zones e g boso and hikurangi a temporary array of seismometers was installed at kilauea in 2007 in anticipation of a slow slip event here we use several established methods to perform a systematic search for tectonic tremor during geodetically defined slow slip events as well as searching for tremor triggered by teleseismic surface waves we do not detect tectonic tremor using any of these methods although we are able to detect episodes of previously identified deep offshore volcanic tremor at 15 20 km depth and volcanic tremor from kilauea although kilauea s seismic network may not be adequate to observe tectonic tremor because hawaii is seismically noisy and its crust is highly attenuating it is also possible that the specific fault conditions on kilauea s decollement are not conducive to such tremor generation

episodic slow slip events and rate and state friction 1 there are several ways of generating episodic slow slip events in models of rate and state friction here i explore the possibility that they arise on velocity weakening faults whose length is tuned in some sense unlike spring block sliders which have a unique critical stiffness for instability elastically deformable faults have multiple length scales stiffnesses relevant to nucleation slow slip events occur when the fault is large enough to initiate an event but too small for that event to reach dynamic instability the available window of lengths depends upon the effective fracture energy of the growing nucleation zone for the aging evolution law this fracture energy increases rapidly with slip speed and the range of permissible lengths increases nearly as b b a where a and b are the coefficients of the velocity and state dependence of the frictional strength this range becomes very large for faults that are near velocity neutral a b however existing lab data firmly favor the slip law as a predictor of nucleation style and for this law the effective fracture energy increases much less rapidly with slip speed the range of fault lengths capable of hosting slow slip events in this case seems too small to explain why they are common to so many subduction zones slow slip can be stabilized over an exceedingly large range of fault lengths if the fracture energy increases with slip speed much more rapidly than for the aging law an appealing mechanism is inelastic dilation of the fault zone coupled with pore pressure reduction and diffusive recovery

fracture energies at the rupture nucleation points of large interplate earthquakes abstract numerical simulations of recurrence of interplate earthquakes in a subduction zone are conducted using a rate and state dependent friction law to estimate the fracture energies at the rupture nucleation points during an interseismic period shear stress is concentrated near the downdip of the locked portion of the plate boundary and seismic rupture initiates when the energy release rate by rupture extension exceeds the fracture energy the simulation results indicate that the fracture energy is proportional to the square of the amount of slip in the deep aseismic zone during the preceding interseismic period this suggests that the fracture energy at the nucleation point can be estimated from the recurrence interval of earthquakes and the relative plate velocity the fracture energies at the rupture nucleation points of great m w 8 nankai earthquakes in southwestern japan are estimated to be 0 1 1 mj m 2 and that of the 2011 m w 9 tohoku oki earthquake to be of the order of 10 mj m 2 the results suggest that fracture energy tends to increase with earthquake magnitude

slow slip slow earthquakes period two cycles full and partial ruptures and deterministic chaos in a single asperity fault abstract the assimilation of geological geophysical and laboratory data in physics based models of fault dynamics promises increasingly realistic simulations of the seismic cycle to assist this effort i explore the dynamics of a single velocity weakening asperity to delineate the relationship between a fault physical properties and the style of faulting during the seismic cycle based on a micro physical model of rate and state friction from a dimensional analysis four non dimensional parameters control the characteristics of slip events and the behavior during the interseismic period including the dieterich ruina rice number ru which is proportional to the ratio of asperity to critical nucleation size w h and rb b a b where a and b control the direct and local evolutionary effects respectively for sufficiently large rb the ru number controls the spectrum of fault slip from periodic slow slip events to aperiodic fast ruptures in finite faults but not in semi infinite faults the transition between these end members includes a bifurcation that involves period two period four period six cycles and deterministic chaos with increasing ru macroscopic fault slip is stabilized as rb vanishes even as ru 1 for finite faults but not for semi infinite faults the transition between slow and fast ruptures for increasing rb includes another type of bifurcation with period two and period four cycles of slow and fast ruptures for 0

gps constraints on 34 slow slip events within the cascadia subduction zone 1997 2005 1 refinements to gps analyses in which we factor geodetic time series to better estimate both reference frames and transient deformation resolve 34 slow slip events located throughout the cascadia subduction zone from 1997 through 2005 timing of transient onset is determined with wavelet transformation of geodetic time series thirty continuous stations are included in this study ranging from northern california to southwestern british columbia our improvements in analysis better resolve the largest creep events and also identify many smaller events at 48 5 n latitude a 14 month average recurrence interval has been observed over eight events since 1997 farther north along vancouver island a host of smaller events with a distinct 14 month periodicity also occurs in southern washington state some of the largest transient displacements are observed but lack any obvious periodicity in their recurrence along central oregon an 18 month recurrence is evident while in northern california an 11 month periodicity continues through 2005 we invert gps offsets of the 12 best recorded events for thrust slip along the plate interface using a cross validation scheme to derive optimal smoothing parameters these 12 events have equivalent moment magnitudes between 6 3 and 6 8 and have 2 3 cm of slip unlike other subduction zones no long duration events are observed and cumulative surface deformation is consistently less than 0 6 cm the many newly resolved smaller transient events in cascadia show that slow slip events occur frequently with gps best capturing only the largest events it is likely that slow slip events occur more frequently at levels not detectable with gps

source scaling relations and along strike segmentation of slow slip events in a 3 d subduction fault model scaling between slip event duration and equivalent moment is diagnostic of the underlying physics of rupture process for episodic slow slip events sses in subduction zones their moment duration relation is not clearly defined and shows considerable variation among individual margins where multiple episodes of sses are geodetically detected here i set up a 3 d planar thrust fault model within the framework of rate state friction to study the spatiotemporal evolution of slip and stress during sses sse source properties including along strike length duration equivalent moment and stress drop are quantified and their scaling relations are compared to observations modeled sses have nearly constant stress drops of 0 001 to 0 01 mpa due to near lithostatic pore pressure at the sse depths the modeled moment duration scaling is between 1 linear and 2 squared when multiple sses appear simultaneously along the strike the stress interaction between approaching slip fronts results in higher average propagation speeds for longer lengths which leads to a scaling close to 2 when sses are well offset in space and time stress interaction is negligible and the scaling is close to 1 two types of sse along strike segmentation gaps are identified from model results the primary gaps are persistent segmentation boundaries due to along strike variation of effective normal stress while the secondary gaps evolve through sse cycles and reflect the stress condition within a primary segment this implies that some geodetically inferred sse segmentation boundaries may result from slower slip velocities below the resolution limits of geodetic inversion models

dilatant strengthening as a mechanism for slow slip events 1 the mechanics of slow slip events sse in subduction zones remain unresolved we suggest that sse nucleate in areas of unstable friction under drained conditions but as slip accelerates dilatancy reduces pore pressure p quenching instability competition between dilatant strengthening and thermal pressurization may control whether slip is slow or fast we model sse with 2 d elasticity rate state friction and a dilatancy law where porosity evolves toward steady state ss over distance dc and ss 0 ln v v0 v is slip speed we consider two diffusion models membrane diffusion md is approximated by p p tf where p and p are shear zone and remote pore pressure and tf is a characteristic diffusion time homogeneous diffusion hd accurately models fault normal flow with diffusivity chyd for md linearized analysis defines a boundary 1 a b between slow and fast slip where f0e b p f0 a and b are friction parameters and is compressibility when 1 a b slip speeds remain quasi static for hd ep eh p defines dilatancy efficiency where h is shear zone thickness and v is plate velocity sse are favored by large eh and low effective stress the ratio ep to thermal pressurization efficiency scales with 1 p so high p favors sse consistent with seismic observations for ep 10 3 transient slip rates repeat times average slip and stress drops are comparable to field observations model updip propagation speeds are comparable to those observed along strike many simulations exhibit slow phases driven by steady downdip slip and faster phases that relax the accumulated stress model sse accommodate only a fraction of plate motion the remaining deficit must be accommodated during coseismic or postseismic slip

the evolution of the seismic aseismic transition during the earthquake cycle constraints from the time dependent depth distribution of aftershocks 1 using the example of the 1992 m 7 3 landers earthquake we show that in the aftermath of a large earthquake the depth extent of aftershocks shows an immediate deepening from pre earthquake levels followed by a time dependent postseismic shallowing we use these seismic data to constrain the change in the depth of the seismic aseismic transition with time throughout the earthquake cycle most studies of the seismic aseismic transition have focussed on the effects of temperature and or lithology on the transition either from brittle faulting to viscous flow or from unstable to stable sliding a strain rate dependent transient deepening of the brittle ductile transition following a major earthquake is predicted by geological and laboratory observations by analyzing the time dependent depth distributions of aftershocks we identify and quantify the temporal evolution of this transition in the example of the landers earthquake its depth changes by as much as 3 km over the course of 4 years

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

dynamic friction in sheared fault gouge implications of acoustic vibration on triggering and slow slip friction and deformation in granular fault gouge are among various dynamic interactions associated with seismic phenomena that have important implications for slip mechanisms on earthquake faults to this end we propose a mechanistic model of granular fault gouge subject to acoustic vibrations and shear deformation the grain scale dynamics is described by the shear transformation zone theory of granular flow which accounts for irreversible plastic deformation in terms of flow defects whose density is governed by an effective temperature our model accounts for stick slip instabilities observed at seismic slip rates in addition as the vibration intensity increases we observe an increase in the temporal advancement of large slip events followed by a plateau and gradual decrease furthermore slip becomes progressively slower upon increasing the vibration intensity the results shed important light on the physical mechanisms of earthquake triggering and slow slip and provide essential elements for the multiscale modeling of earthquake ruptures in particular the results suggest that slow slip may be triggered by tremors

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

slow earthquakes coincident with episodic tremors and slow slip events we report on the very low frequency earthquakes occurring in the transition zone of the subducting plate interface along the nankai subduction zone in southwest japan seismic waves generated by very low frequency earthquakes with seismic moment magnitudes of 3 1 to 3 5 predominantly show a long period of about 20 seconds the seismicity of very low frequency earthquakes accompanies and migrates with the activity of deep low frequency tremors and slow slip events the coincidence of these three phenomena improves the detection and characterization of slow earthquakes which are thought to increase the stress on updip megathrust earthquake rupture zones

strengths of serpentinite gouges at elevated temperatures serpentinite has been proposed as a cause of both low strength and aseismic creep of fault zones to test these hypotheses we have measured the strength of chrysotile lizardite and antigorite rich serpentinite gouges under hydrothermal conditions with emphasis on chrysotile which has thus far received little attention at 25 c the coefficient of friction of chrysotile gouge is roughly 0 2 whereas the lizardite and antigorite rich gouges are at least twice as strong the very low room temperature strength of chrysotile is a consequence of its unusually high adsorbed water content when the adsorbed water is removed chrysotile is as strong as pure antigorite gouge at room temperature heating to 200 c causes the frictional strengths of all three gouges to increase limited data suggest that different polytypes of a given serpentine mineral have similar strengths thus deformation induced changes in polytype should not affect fault strength at 25 c the chrysotile gouge has a transition from velocity strengthening at low velocities to velocity weakening at high velocities consistent with previous studies at temperatures up to 200 c however chrysotile strength is essentially independent of velocity at low velocities overall chrysotile has a restricted range of velocity strengthening behavior that migrates to higher velocities with increasing temperature less information on velocity dependence is available for the lizardite and antigorite gouges but their behavior is consistent with that outlined for chrysotile the marked changes in velocity dependence and strength of chrysotile with heating underscore the hazards of using room temperature data to predict fault behavior at depth the velocity behavior at elevated temperatures does not rule out serpentinite as a cause of aseismic slip but in the presence of a hydrostatic fluid pressure gradient all varieties of serpentine are too strong to explain the apparent weakness of faults such as the san andreas

earthquake supercycles as part of a spectrum of normal fault slip styles like thrust boundaries in subduction zones some normal faults show evidence of temporally transient slip patterns such as temporally clustered earthquakes or periods of elevated creep rate we create rate and state friction numerical models to assess whether typical distributions of frictional parameters can explain transient slip on normal faults we constrain our models with geometry from the wasatch fault zone where 5 10 kyr timescale earthquake clusters are recorded on fault scarps we use numerical models to test whether these earthquake clusters could be the geologic representation of supercycles which we define as long period stress cycles containing multiple seismic cycles field observations laboratory data and analogue experiments suggest that the ratio of velocity weakening to velocity strengthening material varies with the ratio of brittle to ductile material in the shear zone we therefore employ a linear transition of frictional parameters with depth to simulate bulk frictional properties of the shear zone we find that for generalized normal faults rate and state friction predicts a spectrum of slip behaviors including steady aseismic creep aseismic transients clustered earthquakes and regular seismic cycle earthquakes the dominant control on slip behavior is the degree of weakening material in the potentially seismogenic fault patch earthquake clusters occur with higher proportions of velocity weakening material which correspond to more competent less ductile shear zone assemblages we find that rate and state friction predicts a wider spectrum of slip behavior on active normal faults than has been previously recognized potentially due to geologic preservation and identification issues

application of probe permeametry to the prediction of two phase flow performance in laminated sandstones lower brent group north sea abstract the rannoch formation lower brent group north sea is an important laminated oil bearing reservoir in the northern north sea recent work has shown that at the estimated field frontal advance rates for the rannoch formation capillary effects in laminated sandstones might significantly affect the two phase oil and water flow characteristics previous published reservoir simulation models of the rannoch have not accounted for this newly acquired probe permeameter measurements have been used to map the fine scale permeability structure and develop geologically reasonable effective properties permeability and capillary pressure data were combined for geologically meaningful groups of laminae to define dynamic pseudo properties absolute permeability relative permeability and capillary pressure by numerical simulation a geological model for packages of lamination was then used to combine these lamina groups at a scale of the grid block the flow performance of this geologically reasonable grid block containing the laminated structure is compared with that of simple models based on conventional procedure i e the arithmetic average in a horizontal direction or harmonic average vertical permeability and rock curves at this scale the formation is highly anisotropic using the more detailed model with quite different flow characteristics in the horizontal and vertical directions the simple homogeneous models show more isotropic recovery characteristics and give significantly higher recoveries for vertical displacements from these findings it is suggested that previous models of the rannoch formation should be modified to include the capillary effects associated with lamination the procedure outlined here is referred to as the geopseudo approach the approach is widely applicable to laminated reservoirs

slow slip events and seismic tremor at circum pacific subduction zones 1 it has been known for a long time that slip accompanying earthquakes accounts for only a fraction of plate tectonic displacements however only recently has a fuller spectrum of strain release processes including normal slow and silent earthquakes or slow slip events and continuous and episodic slip been observed and generated by numerical simulations of the earthquake cycle despite a profusion of observations and modeling studies the physical mechanism of slow slip events remains elusive the concurrence of seismic tremor with slow slip episodes in cascadia and southwestern japan provides insight into the process of slow slip a perceived similarity between subduction zone and volcanic tremor has led to suggestions that slow slip involves fluid migration on or near the plate interface alternatively evidence is accumulating to support the notion that tremor results from shear failure during slow slip global observations of the location spatial extent magnitude duration slip rate and periodicity of these aseismic slip transients indicate significant variation that may be exploited to better understand their generation most slow slip events occur just downdip of the seismogenic zone consistent with rate and state dependent frictional modeling that requires unstable to stable transitional properties for slow slip generation at a few convergent margins the occurrence of slow slip events within the seismogenic zone makes it highly likely that transitions in frictional properties exist there and are the loci of slow slip nucleation slow slip events perturb the surrounding stress field and may either increase or relieve stress on a fault bringing it closer to or farther from earthquake failure respectively this paper presents a review of slow slip events and related seismic tremor observed at plate boundaries worldwide with a focus on circum pacific subduction zones trends in global observations of slow slip events suggest that 1 slow slip is a common phenomena observed at almost all subduction zones with instrumentation capable of recording it 2 different frictional properties likely control fast versus slow slip 3 the depth range of slow slip may be related to the thermal properties of the plate interface and 4 the equivalent seismic moment of slow slip events is proportional to their duration mo different from the mo 3 scaling observed for earthquakes

slip partitioning along an idealized subduction plate boundary at deep slow slip conditions abstract below the base of many subduction seismogenic zones the plate interface periodically slips at rates 1 to 2 orders of magnitude faster than tectonic plate velocities a number of competing hypotheses exist to explain the mechanisms for these slow slip events sses but they remain incompletely tested because we do not know how deformation is partitioned across the lithologically complex plate boundary interface we use the deepest exposure of the arosa zone a 520 m thick exhumed subduction interface as a case study to evaluate the partitioning of strain between lithologic units throughout the sse cycle we review and synthesize published constitutive relations for the five lithologic units present to express shear stress as a function of deformation rate we use these results to predict 1 the shear stress across the plate boundary as a function of slip velocity and 2 the partitioning of deformation among the different lithologic units for sse and aseismic creep velocities we conduct this analysis for pore fluid pressures from hydrostatic to near lithostatic our results show that at pore fluid pressure close to hydrostatic aseismic creep and sse velocities occur by viscous deformation of calcareous and quartzose units however once the pore fluid pressure increases above 80 of lithostatic plate boundary slip migrates from the calcareous and quartzose rocks during aseismic creep to frictional deformation of talc schist during slow slip this result is insensitive to differences in the thicknesses of metasedimentary units that may be present along subduction plate boundaries and therefore may apply to subduction plate boundaries in general

on the evolution of elastic properties during laboratory stick slip experiments spanning the transition from slow slip to dynamic rupture the physical mechanisms governing slow earthquakes remain unknown as does the relationship between slow and regular earthquakes to investigate the mechanism s of slow earthquakes and related quasi dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration we reproduced the full spectrum of slip behavior from slow to fast stick slip by altering the elastic stiffness of the loading apparatus k to match the critical rheologic stiffness of fault gouge kc our experiments show an evolution from stable sliding when k kc to quasi dynamic transients when k kc to dynamic instabilities when k kc to evaluate the microphysical processes of fault weakening we monitored variations of elastic properties we find systematic changes in p wave velocity vp for laboratory seismic cycles during the coseismic stress drop seismic velocity drops abruptly consistent with observations on natural faults in the preparatory phase preceding failure we find that accelerated fault creep causes a vp reduction for the complete spectrum of slip behaviors our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults depending on frictional properties in agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by vp changes during the seismic cycle the observed reduction in vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors

dynamic triggering of creep events in the salton trough southern california by regional m 5 4 earthquakes constrained by geodetic observations and numerical simulations abstract since a regional earthquake in 1951 shallow creep events on strike slip faults within the salton trough southern california have been triggered at least 10 times by m 5 4 earthquakes within 200 km the high earthquake and creep activity and the long history of digital recording within the salton trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes here we document the history of fault creep events on the superstition hills fault based on data from creepmeters insar and field surveys since 1988 we focus on a subset of these creep events that were triggered by significant nearby earthquakes we model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate and state dependent friction we find that the static stress changes from the causal earthquakes are less than 0 1 mpa and too small to instantaneously trigger creep events in contrast we can reproduce the characteristics of triggered slip with dynamic perturbations alone the instantaneous triggering of creep events depends on the peak and the time integrated amplitudes of the dynamic coulomb stress change based on observations and simulations the stress change amplitude required to trigger a creep event of a 0 01 mm surface slip is about 0 6 mpa this threshold is at least an order of magnitude larger than the reported triggering threshold of non volcanic tremors 2 60 kpa and earthquakes in geothermal fields 5 kpa and near shale gas production sites 0 2 0 4 kpa which may result from differences in effective normal stress fault friction the density of nucleation sites in these systems or triggering mechanisms we conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the superstition hills fault

frictional behavior of oceanic transform faults and its influence on earthquake characteristics 1 we use a three dimensional strike slip fault model in the framework of rate and state dependent friction to investigate earthquake behavior and scaling relations on oceanic transform faults otfs gabbro friction data under hydrothermal conditions are mapped onto otfs using temperatures from 1 a half space cooling model and 2 a thermal model that incorporates a visco plastic rheology non newtonian viscous flow and the effects of shear heating and hydrothermal circulation without introducing small scale frictional heterogeneities on the fault our model predicts that an otf segment can transition between seismic and aseismic slip over many earthquake cycles consistent with the multimode hypothesis for otf ruptures the average seismic coupling coefficient c is strongly dependent on the ratio of seismogenic zone width w to earthquake nucleation size h c increases by four orders of magnitude as w h increases from 1 to 2 specifically the average c 0 15 0 05 derived from global otf earthquake catalogs can be reached at w h 1 2 1 7 further in all simulations the area of the largest earthquake rupture is less than the total seismogenic area and we predict a deficiency of large earthquakes on long transforms which is also consistent with observations to match these observations over this narrow range of w h requires an increase in the characteristic slip distance dc as the seismogenic zone becomes wider and normal stress is higher on long transforms earthquake magnitude and distribution on the gofar and romanche transforms are better predicted by simulations using the visco plastic model than the half space cooling model

spatial temporal patterns of seismic tremors in northern cascadia 1 we study in detail the two consecutive episodic tremor and slip ets events that occurred in the northern cascadia subduction zone during 2003 and 2004 for both sequences the newly developed source scanning algorithm ssa is applied to seismic waveform data from a dense regional seismograph array to determine the precise locations and origin times of seismic tremors in map view the majority of the tremors occurred in a limited band bounded approximately by the surface projections of the 30 km and 50 km depth contours of the plate interface the horizontal migration of tremor occurrence is from southeast to northwest with an average speed of 5 km d in cross section tremors in both sequences span a depth range of over 40 km across the interface with the majority occurring in the overriding continental crust in particular 50 55 of them are located within 2 5 km from the strong seismic reflector bands above the plate interface the lack of vertical migration implies that a slow diffusion process in the vertical direction cannot be responsible for tremor occurrences the source spectra of tremors clearly lack high frequency content 5 hz relative to local earthquakes we propose two possible models to explain the relationship between slip and tremors the first one regards ets tremors as the manifestation of hydroseismogenic processes in response to the temporal strain variation associated with the episodic slip along the lower portion of the plate interface downdip from the locked zone in the second model tremors and slip are associated with the same process along the same structure in a distributed deformation zone across the plate interface neither model can be dismissed conclusively at this stage

nucleation process of magnitude 2 repeating earthquakes on the san andreas fault predicted by rate and state fault models with safod drill core data recent laboratory shear slip experiments conducted on a nominally flat frictional interface reported the intriguing details of a two phase nucleation of stick slip motion that precedes the dynamic rupture propagation this behavior was subsequently reproduced by a physics based model incorporating laboratory derived rate and state friction laws however applying the laboratory and theoretical results to the nucleation of crustal earthquakes remains challenging due to poorly constrained physical and friction properties of fault zone rocks at seismogenic depths here we apply the same physics based model to simulate the nucleation process of crustal earthquakes using unique data acquired during the san andreas fault observatory at depth safod experiment and new and existing measurements of friction properties of safod drill core samples using this well constrained model we predict what the nucleation phase will look like for magnitude 2 repeating earthquakes on segments of the san andreas fault at a 2 8 km depth we find that despite up to three orders of magnitude difference in the physical and friction parameters and stress conditions the behavior of the modeled nucleation is qualitatively similar to that of laboratory earthquakes with the nucleation consisting of two distinct phases our results further suggest that precursory slow slip associated with the earthquake nucleation phase may be observable in the hours before the occurrence of the magnitude 2 earthquakes by strain measurements close a few hundreds meters to the hypocenter in a position reached by the existing borehole

sound velocities of δ alooh up to core mantle boundary pressures with implications for the seismic anomalies in the deep mantle recent studies show that alooh is stable up to the base of the mantle this phase is therefore a possible carrier and host of water in the deep mantle to uncover the physical properties of alooh under deep mantle pressure conditions we have conducted high pressure acoustic wave velocity measurements of alooh by using brillouin spectroscopy combined with high pressure raman spectroscopic measurements in a diamond anvil cell up to pressures of 134 gpa there is a precipitous increase by 14 in the acoustic velocities of alooh from 6 to 15 gpa which suggests that pressure induced o h bond symmetrization occurs in this pressure range the best fit values for the high pressure form of alooh of k0 190 2 gpa g0 160 0 9 gpa k p 0 k0 3 7 1 and g p 0 g0 1 32 1 indicate that alooh has a 20 30 higher vs value compared to those of the major constituent minerals in the mantle transition zone such as wadsleyite ringwoodite and majorite on the other hand the vs of alooh is 7 lower than that of mg bridgmanite under lowermost mantle pressure conditions because of the significantly lower value of the pressure derivative of the shear modulus by comparing our results with seismic observations we can infer that alooh could be one of the potential causes of a positive vs anomaly observed at 600 km depth beneath the korean peninsula and a negative vs jump near 2800 km depth near the northern margin of the large low shear velocity province beneath the pacific

stabilizing effect of high pore fluid pressure on slip behaviors of gouge bearing faults this work is supported by the department of energy office of science the office of basic energy sciences chemical sciences geosciences biosciences division under award no de fg 0207er15916 and by the national science foundation under grant no ear 1761912

overlapping regions of coseismic and transient slow slip on the hawaiian decollement abstract earthquakes and slow slip are different faulting processes that release accumulated stress on different time scales despite nearly two decades of study it is still unclear whether the same section of fault is capable of hosting both slow aseismic and fast seismic slip here we jointly invert gps strong motion records and empirically corrected tsunami waveforms for the 2018 m7 1 hawai i earthquake our inversion results suggest the earthquake had a slow rupture speed of 1 2 km s with a maximum slip of 3 m south east of the hypocenter extending to the south west through an area known to regularly host slow slip events after exploring how the choice of fault geometry and regularization parameters affect the slip distributions of the earthquake and slow slip events we find strong evidence of overlap between the two additionally we perform numerical modeling to simulate fast and slow slip behavior due to the homogeneity of the hawaiian decollement differences in effective stress are likely an important factor that causes the diversity of slip we find that an earthquake can completely penetrate into the slow slip zone provided the effective stress differences between fast and slow slip zones is large enough to facilitate this our results reinforce the idea that an individual section of fault is capable of hosting a variety of distinct slip behaviors this is important for estimating earthquake rupture extent and for better ground motion and tsunami hazard assessment

earthquake nucleation on faults with rate and state dependent strength abstract dieterich j h 1992 earthquake nucleation on faults with rate and state dependent strength in t mikumo k aki m ohnaka l j ruff and p k p spudich editors earthquake source physics and earthquake precursors tectonophysics 211 115 134 faults with rate and state dependent constitutive properties reproduce a range of observed fault slip phenomena including spontaneous nucleation of slip instabilities at stresses above some critical stress level and recovery of strength following slip instability calculations with a plane strain fault model with spatially varying properties demonstrate that accelerating slip precedes instability and becomes localized to a fault patch the dimensions of the fault patch follow scaling relations for the minimum critical length for unstable fault slip the critical length is a function of normal stress loading conditions and constitutive parameters which include dc the characteristic slip distance if slip starts on a patch that exceeds the critical size the length of the rapidly accelerating zone tends to shrink to the characteristic size as the time of instability approaches solutions have been obtained for a uniform fixed patch model that are in good agreement with results from the plane strain model over a wide range of conditions above the steady state stress the logarithm of the time to instability linearly decreases as the initial stress increases because nucleation patch length and premonitory displacement are proportional to dc the moment of premonitory slip scales by d3c the scaling of dc is currently an open question unless dc for earthquake faults is significantly greater than that observed on laboratory faults premonitory strain arising from the nucleation process for earthquakes may by too small to detect using current observation methods excluding the possibility that dc in the nucleation zone controls the magnitude of the subsequent earthquake then the source dimensions of the smallest earthquakes in a region provide an upper limit for the size of the nucleation patch

spontaneous and triggered aseismic deformation transients in a subduction fault model 1 aseismic deformation transients can emerge as a natural outcome of the rate and state friction processes revealed in laboratory fault sliding experiments when that constitutive formulation is applied to model subduction earthquake sequences transients can arise spontaneously for certain effective stress variations with depth we show that if interstitial fluids are present and pore pressure is near lithostatic around and downdip from the frictional stability transition transients with recurrence intervals of 1 year are predicted on the basis of laboratory friction parameters and their temperature hence depth variations the recurrence interval decreases with and reaches 14 months when is 2 3 mpa dimensional analysis and numerical studies show that the fault response primarily depends on a parameter w h here the high pore pressure zone extends distance w updip from the stability transition and h is the stable patch size for steady sliding evidence that such fluid conditions may actually be present is independently provided by the occurrence of nonvolcanic tremors as apparent responses to extremely small stress changes and by petrological constraints on expected regions of dehydration for the shallow dipping subduction zones where transients are observed transient sequences can also be triggered by a modest one time step like interseismic stress perturbation on the subduction fault due to nearby earthquakes or to pore pressure changes e g during episodes of metamorphic fluid release properties of triggered transients and future thrust earthquakes depend on the interseismic time when the perturbation is introduced its relative location along the subduction fault and its magnitude

fault frictional parameters and material properties revealed by slow slip events at kilauea volcano hawai i 1 we categorize slow slip events at kilauea volcano into two distinct families based on gps measurements of the surface displacement patterns an event correlation filter confirms that eastern and western families are statistically distinguishable with the western family notably self similar the western family exhibits quasi periodicity with regular repeat times while eastern family events are aperiodic or have complicated periodicity if the decollement is the source fault for both families of events it must have varying frictional properties at the 10 km scale of separation the temporal slip and spatial scaling behavior are consistent with a simplistic rate and state dependent frictional formalism provided that the characteristic slip distance for state evolution dc is of the order of millimeters rather than the 10 100 m typically found in lab studies and the shear rigidity is around 2 gpa consistent with fault gouge material

complementary slip distributions of the largest earthquakes in the 2012 brawley swarm imperial valley california we investigate the finite rupture processes of two m 5 earthquakes in the 2012 brawley swarm by joint inversion of nearby strong motion and high rate gps data waveform inversions up to 3 hz were made possible by using a small event m w3 9 for path calibration of the velocity structure our results indicate that the first m w5 3 event ruptured a strong concentrated asperity with offsets of 20 cm centered at a depth of 5 km the subsequent m w5 4 event occurred 1 5 h later with a shallower slip distribution that surrounds and is complementary to that of the earlier event the second event has a longer rise time and weaker high frequency energy release compared to the m w5 3 event both events display strong rupture directivity toward the southwest and lack of very shallow 2 km coseismic slip the hypocenters for these events appear to be near or in the bedrock but most of the slip is distributed at shallower depths 6 km and can explain a large part of the gps offsets for the swarm the complementary slip distributions of the two events suggest a triggering relationship between them with no significant creep needed to explain the various data sets

episodic tremors and slip in cascadia in the framework of the frenkel kontorova model received 27 august 2010 revised 20 october 2010 accepted 28 october 2010 published 13 january 2011 1 the seismic moment for regular earthquakes is proportional to the cube of rupture time a second class of phenomena collectively called slow earthquakes has very different scaling we propose a model inspired from the phenomenology of dislocation dynamics in crystals that is consistent with the scaling relations observed in the cascadia episodic tremor and slip ets events two fundamental features of ets are periodicity and migration in the northern cascadia subduction zone ets events appear every 14 5 months or so during these events tremors migrate along strike with a velocity of 10 km day and simultaneously zip back and forth in the relative plate motion direction with at ypical velocity of 50 km h our model predicts the formation of a sequence of slip pulses on the boundary of the plates which describes the major features of fault dynamics including periodicity and the migration pattern of tremors citation gershenzon n i g bambakidis e hauser a ghosh and k c creager 2011 episodic tremors and slip in cascadia in the framework of the frenkel kontorova model geophys res lett 38 l01309

evidence suggesting fluid flow beneath japan due to periodic seismic triggering from the 2004 sumatra andaman earthquake 1 we show that very large surface waves from the 2004 sumatra andaman earthquake m9 2 triggered deep low frequency dlf seismic tremors beneath japan over a 500 km wide region the triggered seismicity was periodically excited synchronized with the amplitudes and phases of the oscillatory surface waves incident on the region periodic excitation implies that the specific phase of the surface waves plays an important role for the triggering estimation of stress changes in the source regions showed that the volumetric dilatation larger than 10 8 was the predominant factor for triggering thereby strongly supporting the hypothesis that dlf events are caused by processes related to fluid flow

symmetry and the critical slip distance in rate and state friction laws 1 we performed laboratory experiments to investigate the processes responsible for rate and state friction rsf behavior in fault rocks we focused on the symmetry of the frictional constitutive response to velocity changes and the mechanics of the critical friction slip distance dc experiments were conducted in double direct shear at 1 and 25 mpa normal stress at room temperature and for shearing velocity from 1 to 300 m s we studied three granular materials and bare surfaces of westerly granite ruina s law which predicts frictional symmetry between velocity increases and decreases better matches our data than dieterich s law which predicts that velocity decreases should evolve to steady state at a smaller displacement however for granular shear in some cases dc is smaller for velocity increases than for velocity decreases contrary to expectations from either law on bare granite surfaces the frictional response is symmetric for velocity increases decreases two distinct length scales for dc and two state variables are required for granular shear in some cases we hypothesize that asymmetry and two state behavior are caused by shear localization and changes in shear fabric in fault gouge our measurements show that during steady state frictional shear dilation after a velocity increase is smaller than compaction after a decrease normal stress oscillations cause a marked decrease in dc reduction of dc reduces frictional stability enhancing the possibility of seismic slip our experiments show that shear localization and fabric within the fault gouge can influence the rsf parameters that dictate earthquake nucleation and dynamic rupture

spatiotemporal evolution of slow slip events in a nonplanar fault model for northern cascadia subduction zone slow slip events sses are identified as the quasi stable fault deformation in the deep transition zone from locked to continuous sliding in many subduction zones in the well instrumented cascadia margin a class of mw6 0 slow slip events arise beneath port angeles every 14 months as inferred from two decades of continuous geodetic monitoring the along strike bending of the incoming oceanic plate beneath north washington is a unique geometric feature whose influence on slow slip processes is still unknown here we incorporate a realistic fault geometry of northern cascadia in the framework of rate and state dependent friction law to simulate the spatiotemporal evolution of slow slip events on a nonplanar subduction fault the modeled sses capture the major characteristics revealed by gps observations the central 150 km long fault segment beneath port angeles acts as a repetitive slip patch where sses appear every 1 5 years with a maximum slip of 2 5 cm two minor slip patches with smaller areas and cumulative slips straddle this central slip patch the along strike segmentation of slow slip is inversely related to the local fault dip and strike angles of the slow slip zone suggesting strong geometrical control on the slow slip process this correlation holds even after removing the effect of w h ratio between velocity weakening sse fault width and characteristic nucleation size besides the gps detectable fast spreading phase we find that each sse cycle consists of deep pre sse preparation and post sse relaxation phases which may be the driving mechanism for the deep tremor activity between major sse episodes discovered in cascadia

intermittent tremor migrations beneath guerrero mexico and implications for fault healing within the slow slip zone slow slip events exhibit significant complexity in slip evolution and variations in recurrence intervals behavior that varies systematically with recurrence interval is likely to reflect different extents of fault healing between these events here we use high resolution tremor catalogs beneath guerrero mexico to investigate the mechanics of slow slip we observe complex tremor propagation styles including rapid tremor migrations propagating either along the main tremor front or backward reminiscent of those in northern cascadia we also find many migrations that originate well behind the front and repeatedly occupy the same source region during a tremor episode similar to those previously reported from shikoku japan these migrations could be driven by slow slip in the surrounding regions with recurrence intervals possibly modulated by tides the propagation speed of these migrations decreases systematically with time since the previous migration over the same source area tremor amplitudes seem consistent with changes in the propagation speeds being controlled primarily by changes in the slip speeds one interpretation is that the high propagation speeds and inferred high slip speeds during the migrations with short recurrence intervals are caused by incomplete healing within the host rock adjacent to the shear zone which could lead to high permeability and reduced dilatant strengthening of the fault gouge similar processes may operate in other slow slip source regions such as cascadia

interaction of slip on asperities numerical simulation of seismic cycles on a two dimensional planar fault with nonuniform frictional property 1 numerical simulation is conducted to understand the variety of frictional sliding on a plate interface and complex recurrence of earthquakes a planar square fault in an infinite uniform elastic medium is considered and the frictional stress on the fault is assumed to obey a rate and state dependent friction law nonuniformity in a frictional constitutive parameter is introduced on the model fault on the fault plane one or two circular patches with velocity weakening frictional property are surrounded by velocity strengthening areas unstable slip may occur for velocity weakening friction and aseismic sliding occurs for velocity strengthening friction velocity weakening patches correspond to asperities because intense seismic slip may occur there simulation results indicate that episodic aseismic slip events slow earthquakes occur when the velocity weakening patch size is close to the critical size of earthquake nucleation propagation of postseismic sliding on the velocity strengthening region follows an earthquake at a velocity weakening patch when the postseismic sliding reaches another velocity weakening patch an earthquake may be triggered at the patch resulting in a double earthquake the time delay between two events of the double earthquake increases with the distance between the two velocity weakening patches or the degree of velocity strengthening in the region between the patches when the distance between the two velocity weakening patches is long an earthquake at one patch does not directly cause an earthquake at the other patch in these cases complex earthquake recurrence may appear due to the interaction between ruptures at the two patches and the recurrence interval of earthquakes and coseismic slip is not constant at each velocity weakening patch

a silent slip event on the deeper cascadia subduction interface continuous global positioning system sites in southwestern british columbia canada and northwestern washington state usa have been moving landward as a result of the locked state of the cascadia subduction fault offshore in the summer of 1999 a cluster of seven sites briefly reversed their direction of motion no seismicity was associated with this event the sudden displacements are best explained by 2 centimeters of aseismic slip over a 50 kilometer by 300 kilometer area on the subduction interface downdip from the seismogenic zone a rupture equivalent to an earthquake of moment magnitude 6 7 this provides evidence that slip of the hotter plastic part of the subduction interface and hence stress loading of the megathrust earthquake zone can occur in discrete pulses