recurrence behavior of short term slow slip and correlated nonvolcanic tremor episodes in western shikoku southwest japan 1 from the national research institute for earth science and disaster prevention hi net tiltmeter data we determine time dependent source processes of seven repeating short term slow slip events sse in the western shikoku region southwest japan over the period from 2002 to 2007 the tiltmeters record clear signals of sses characterized by a slow rise a week long duration and a magnitude on the order of 10 2 10 1 rad we apply a time dependent slip inversion method to the tilt records for the seven sses for each sse a slip area migrates in the strike direction of the subducting slab at a rate of 10 km d 1 comparing the slow slip area with epicenters of accompanying nonvolcanic tremors in subday time resolution we find that the two phenomena are located on a smaller area than previously reported and migrate as a group a moment rate function for each sse exhibits good correlation with the temporal change in tremor activity a comparison of the slip distributions of all of the analyzed sses shows that there is a patch of slow slip area 30 km in diameter that is shared by all of the episodes in addition the location of the slip patch is in good agreement with the epicenters of tremors and very low frequency earthquakes these lines of evidence suggest that the identified slip patch is one of the main slow slip patches in the region and a recurrence of sses may be controlled by the patch and that these slow earthquakes might be different manifestations of a single slip process on the deep plate interface

dynamic modeling of slow slip coupled with tremor 1 we theoretically study the generation mechanism of slow slip in a dynamical framework assuming a fault in a fluid saturated thermoporoelastic medium the fluid flow is taken into consideration dynamic slip is assumed to create pores and cause shear heating on the fault key parameters in the modeling are su and su the nondimensional parameter su represents the relative dominance of the effect of pore creation on the fluid pressure change over that of shear heating while su is associated with the dominance of fluid flow effect over the effect of shear heating our calculation shows that we have to assume su 1 and relatively small values for su to simulate rupture speed that is negligibly small compared to the shear wave velocity although this was also found in our former paper our new finding here is the simulation of slow slip coupled with tremor we find that frozen slip is reactivated sporadically because the fluid inflow triggered by the pore creation elevates the fluid pressure on the fault the slip reactivation actually occurs if su is smaller than a threshold such sporadic reactivation of slips can be a model for slow slip coupled with tremor we also show that the moment evolution curves are categorized into two separate groups when su 0 1 one of them represents slow slips while the other represents ordinary earthquakes

complexity of the deep san andreas fault zone defined by cascading tremor seismic tremors can be used to distinguish plate boundaries analysis of tremors occurring deep beneath the san andreas fault may identify the boundary between the north american plate and the preserved remnant of a subducted slab

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

propagation of slow slip leading up to the 2011 mw 9 0 tohoku oki earthquake many large earthquakes are preceded by one or more foreshocks but it is unclear how these foreshocks relate to the nucleation process of the mainshock on the basis of an earthquake catalog created using a waveform correlation technique we identified two distinct sequences of foreshocks migrating at rates of 2 to 10 kilometers per day along the trench axis toward the epicenter of the 2011 moment magnitude mw 9 0 tohoku oki earthquake in japan the time history of quasi static slip along the plate interface based on small repeating earthquakes that were part of the migrating seismicity suggests that two sequences involved slow slip transients propagating toward the initial rupture point the second sequence which involved large slip rates may have caused substantial stress loading prompting the unstable dynamic rupture of the mainshock

dynamic modeling of slow earthquakes based on thermoporoelastic effects and inelastic generation of pores 1 we numerically simulate features of slow earthquakes to understand their generation mechanism in the framework of dynamic modeling their typical features will be that the fault rupture velocity and stress drop are markedly lower than those of ordinary earthquakes we assume a fault in a thermoporoelastic medium taking account of fluid flow and inelastic creation of pores on the fault this paper is an extension of our studies published in the work of suzuki and yamashita 2006 2007 2008 in which a nondimensional parameter su was shown to play a critical role in dynamic fault rupture the parameter su represents the dominance of the effect of inelastic pore creation over that of frictional heating under the condition of no fluid flow however it can be shown that su plays an important role even if the fluid flow is considered in the present study we successfully simulate slow fault rupture growth and low stress drop which characterize the slow earthquakes critical ingredients of our modeling are assumptions of 1 su considerably larger than assumed for the simulation of ordinary earthquakes 2 fluid flow into the inelastically created pores and 3 initial shear stress significantly smaller than assumed for the simulation of ordinary earthquakes the assumption of a large value of su corresponds to that of a slip resistant and low stress drop zone the fluid inflow can promote the fault rupture in the slip resistant zone

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

inactive and relict rock glaciers of the deboullie lakes ecological reserve northern maine usa lobate talus slopes in the deboullie lakes ecological reserve dler of northern maine exhibit parabolic profiles characteristic of inactive and relict talus derived rock glaciers vegetated rock glacier surfaces suggest that the landforms are no longer active and lobes comprising two dler rock glaciers document periods of past growth observations of perennial subsurface ice are supported by datalogger temperature measurements indicating that sporadic permafrost exists throughout the dler we compare the dler rock glaciers along with similar features elsewhere in new england and adjacent quebec to the modern alpine permafrost distribution results indicate that a mean annual temperature cooling of 68c is required to promote active rock glacier growth ages of plant remains recovered from the basal sediments of a local pond constrain deglaciation to before 11 320 14 c a bp and core stratigraphy and organic content reveal that a periglacial environment persisted during the early postglacial era thus we hypothesise that the dler rock glaciers were active during lateglacial time despite the lack of glacier activity in the region we take this to suggest that north eastern us rock glaciers formed in response to mean annual temperatures skewed towards the frigid winters of the younger dryas chronozone copyright 2009 john wiley sons ltd

generation mechanism of slow earthquakes numerical analysis based on a dynamic model with brittle ductile mixed fault heterogeneity 1 various characteristics have been discovered for small slow earthquakes occurring along subduction zones which are deep nonvolcanic tremor low frequency earthquakes lfes and very low frequency earthquakes vlfs in this study we model these slow earthquakes using a dynamic model consisting of a cluster of frictionally unstable patches on a stable background the controlling parameters in our model are related to the patch distribution and the viscosity of both the patches and the background by decreasing patch density or increasing viscosity we observed the transition in rupture propagation mechanism that is from fast elastodynamic interactions characterized by an elastic wave propagation to slow diffusion limited by viscous relaxation times of traction on fault patches and or background some sets of these geometrical and frictional parameters collectively explain the moment rate functions source spectra and scaled energy of observed slow earthquakes in addition we successfully explain both parabolic and constant velocity migrations in the case of the diffusion limited rupture therefore the observed various characteristics of tremor lfes vlfs and potentially slow slip events may be essentially explained by our simple model with a few parameters describing source structures and frictional properties of brittle ductile transition zones along plate boundaries

reconsidering earthquake scaling the relationship scaling between scalar moment m0 and duration t potentially provides key constraints on the physics governing fault slip the prevailing interpretation of m0 t observations proposes different scaling for fast earthquakes and slow mostly aseismic slip populations and thus fundamentally different driving mechanisms we show that a single model of slip events within bounded slip zones may explain nearly all fast and slow slip m0 t observations and both slip populations have a change in scaling where the slip area growth changes from 2 d when too small to sense the boundaries to 1 d when large enough to be bounded we present new fast and slow slip m0 t observations that sample the change in scaling in each population which are consistent with our interpretation we suggest that a continuous but bimodal distribution of slip modes exists and m0 t observations alone may not imply a fundamental difference between fast and slow slip

phenomenology of deep slow earthquake family in southwest japan spatiotemporal characteristics and segmentation 1 the phenomenology of deep slow earthquakes including low frequency tremors very low frequency earthquakes and short term slow slip events on the subducting plate interface in southwest japan is investigated on the basis of their spatiotemporal characteristics the belt like distribution of tremors is divided into segments bounded by gaps the repetition of tremor episode depends on the magnitude of the episode which is defined by the number of detected tremors within each episode major tremor episodes with a large number of detected tremors recur at an interval of approximately 6 months accompanying the short term slow slip events in large segments in small segments tremor episodes with small numbers of tremors have recurrence intervals of a few months some of them occasionally accompany the slight ground tilting caused by a small size slow slip event even in the same segment there exist different recurrence intervals according to the magnitude of the tremor episode the migration pattern varies greatly in initiation termination direction and speed however the migration direction has a general tendency for each segment on both sides of the gap the tremor starts next to the gap and propagates to the other side assuming all tremor episodes are caused by slow slip events the equivalent moment and slip are estimated from the number of detected tremor counts and the area of each tremor episode the equivalent slip history estimated from all tremor episodes is almost constant in each segment this indicates that tremor activity is a good proxy for slow slips

splay fault branching from the hikurangi subduction shear zone implications for slow slip and fluid flow gns science s mbie funded contracts grant number co5x1204 and c05x0908 gas hydrates resources marsden fund project grant number gns0902

tidal sensitivity of tectonic tremors in nankai and cascadia subduction zones tectonic tremors in subduction zones which result from slip at the deep plate interface are known to exhibit a 12 4 h periodicity in their activity due to tidal influence because tidal stress can be calculated quantitatively the response of the plate interface can yield quantitative information about its frictional property the relation between tremor rate and tidal stress is investigated and an exponential relation is widely confirmed as observed by previous studies this study particularly focuses on spatial variations of tidal sensitivity which are compared with spatial variations of tremor duration and amplitude the sensitivity is quantitatively defined by the exponent of the exponential relation which can be related to the parameter a or a b in the rate and state friction law where is effective normal stress on the shallower tremor zone short duration and large amplitude tremors occur followed by more sensitive tremors meanwhile deeper tremors with longer duration and smaller amplitude show lower sensitivity although along strike variation also exists typical and maximum sensitivities estimated here imply values for a or a b of about 3 and 1 kpa respectively these correlations are consistent with a model in which the plate interface consists of a velocity strengthening background with embedded velocity weakening regions the frictional heterogeneity may be statistically characterized by cluster size and density of the velocity weakening regions and controls the overall slip behavior the observed depth dependency of tremor duration amplitude and sensitivity implies that frictional heterogeneity is controlled by physical quantities varying with depth such as temperature or fluid amount

a slow slip event triggered by teleseismic surface waves 1 in recent years slow slip events sse have been observed to occur at regular intervals on the deep portions of subduction zone interfaces these are accompanied by seismic tremor that occurs over their duration it has been observed that tremor activity shows transient modulations in response to earth tides and the passage of seismic waves from distant earthquakes here we show for the first time geodetic evidence for the triggering of an interplate sse itself by teleseismic surface waves this sse in southwest japan which had an equivalent magnitude mw 5 3 and duration of 1 5 days was triggered by the surface waves of a mw 7 6 earthquake in tonga this evidence was captured by a newly deployed sensitive strainmeter network the triggered sse occurred on a place on the plate interface where the recurrence time for such events had almost expired whereas other regions at up to 90 of the recurrence time were not triggered this provides information for the conditions for triggering and generation of sses and perhaps for regular earthquakes

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

rapid continuous streaking of tremor in cascadia nonvolcanic tremor is a recently discovered weak seismic signal associated with slow slip on a fault plane and has potential to answer many questions about how faults move its spatiotemporal distribution however is complex and varies over different time scales and the causal physical mechanisms remain unclear here we use a beam backprojection method to show rapid continuous slip parallel streaking of tremor over time scales of several minutes to an hour during the may 2008 episodic tremor and slip event in the cascadia subduction zone the streaks propagate across distances up to 65 km primarily parallel to the slip direction of the subduction zone both updip and downdip at velocities ranging from 30 to 200 km h we explore mainly two models that may explain such continuous tremor streaking the first involves interaction of slowly migrating creep front with slip parallel linear structures on the fault the second is pressure driven fluid flow through structurally controlled conduits on the fault both can be consistent with the observed propagation velocities and geometries although the second one requires unlikely condition in addition we put this new observation in the context of the overall variability of tremor behavior observed over different time scales

propagation dynamics of seismic and aseismic slip governed by fault heterogeneity and newtonian rheology 1 slow earthquakes called episodic tremor and slip ets events propagate over 100 km at low average velocities 10 km per day along several plate interfaces accompanying seismic and aseismic slip these low propagation velocities differentiate slow earthquakes from ordinary earthquakes and thus understanding their propagation processes is fundamental to understanding the poorly constrained physics governing the diversity and universality of earthquakes we show that rheological heterogeneity on faults primarily governs ets propagation on the basis of comprehensive modeling and observations that correlate migration patterns with the energetics of tremor on a plate bounding fault in southwest japan the fault has persistent small scale segmentation in which ets events started propagating energetically in relatively brittle sections and decelerated generally with a parabolic pattern in relatively ductile sections simulated spontaneous ruptures that are based on these parabolic tremor migration patterns constrain the cause of ductility to newtonian plastic flow or perhaps dilatant strengthening but reject large scale fluid flows we discuss possible elementary processes underlying the newtonian rheology this model is also consistent with the observed seismicity migration pattern before the 2011mw9 0 tohoku oki earthquake suggesting delayed triggering by themw 7 3 foreshock

brittle and ductile friction and the physics of tectonic tremor 1 observations of nonvolcanic tremor provide a unique window into the mechanisms of deformation and failure in the lower crust at increasing depths rock deformation gradually transitions from brittle where earthquakes occur to ductile with tremor occurring in the transitional region the physics of deformation in the transition region remain poorly constrained limiting our basic understanding of tremor and its relation to earthquakes we combine field and laboratory observations with a physical friction model comprised of brittle and ductile components and use the model to provide constraints on the friction and stress state in the lower crust a phase diagram is constructed that characterizes under what conditions all faulting behaviors occur including earthquakes tremor silent transient slip and steady sliding our results show that tremor occurs over a range of ductile and brittle frictional strengths and advances our understanding of the physical conditions at which tremor and earthquakes take place

striations duration migration and tidal response in deep tremor deep tremor in subduction zones is thought to be caused by small repeating shear slip events on the plate interface with significant slow components it occurs at a depth of about 30 kilometres and provides valuable information on deep plate motion and shallow stress accumulation on the fault plane of megathrust earthquakes tremor has been suggested to repeat at a regular interval migrate at various velocities and be modulated by tidal stress here i show that some time invariant interface property controls tremor behaviour using precise location of tremor sources with event duration in western shikoku in the nankai subduction zone japan in areas where tremor duration is short tremor is more strongly affected by tidal stress and migration is inhibited where tremor lasts longer diffusive migration occurs with a constant diffusivity of 10 4 m 2 s 1 the control property may be the ratio of brittle to ductile areas perhaps determined by the influence of mantle wedge serpentinization on the plate interface the spatial variation of the controlling property seems to be characterized by striations in tremor source distribution which follows either the current or previous plate subduction directions this suggests that the striations and corresponding interface properties are formed through the subduction of inhomogeneous structure such as seamounts for periods as long as ten million years

rapid tremor reversals in cascadia generated by a weakened plate interface slow slip of the down going plate at subduction zones can generate seismic tremor analysis of recent large tremor and slip episodes along the cascadia subduction zone reveals tremor signals that reverse and rapidly migrate back along the previously ruptured fault implying that the initial fault slip weakened the plate interface

thermal and metamorphic environment of subduction zone episodic tremor and slip 1 episodic tremor and slip ets have been detected in the cascadia and southwest japan subduction zones where the subducting crust is relatively warm because of the young incoming lithosphere 20 ma and modest plate convergence rates 40 60 mm a in the southwest japan subduction zone low frequency earthquakes occur on the plate interface at depths of 30 35 km beneath shikoku where finite element thermal models predict temperatures of 425 c in the subducting oceanic crust and at depths of 30 40 km beneath the kii peninsula where predicted temperatures are 325 c warmer temperatures of 575 c are predicted at ets depths beneath southern vancouver island in the cascadia subduction zone but here tremor also occurs within the overlying fore arc crust where temperatures are lower in the southwest japan and cascadia subduction zones subducting oceanic crust passes through the blueschist greenschist and amphibolite metamorphic facies where mineral dehydration reactions are complex the different temperatures predicted for the two subduction zones suggest that ets does not coincide with a specific temperature or metamorphic reaction several lines of evidence indicate that a free h2o rich fluid is present at least transiently in subducting oceanic crust and fluids released by prograde metamorphic dehydration reactions may help trigger or enable ets within the subducting plate less clear is the role h2o may play in tremor observed in the cascadia fore arc crust where free h2o may exist locally in faults and fractures but retrograde hydration reactions are expected to consume h2o

a slip pulse model with fault heterogeneity for low frequency earthquakes and tremor along plate interfaces 1 deep low frequency earthquakes lfes and nonvolcanic tremor have distinctive characteristics unlike those of regular earthquakes including strong anisotropy in their migration velocity and source spectra displaying 1 f decay we show that a physical model can explain these features in a simple framework with slip pulses originating on fault heterogeneity and triggered by slow slip events lfe tremor source areas in the model consist of unstable patches sparsely and heterogeneously distributed following a gaussian distribution the difference in their migration speeds along dip and along strike was reproduced without anisotropic rheological properties by introducing alignments of their sources similar to observed streaks of lfes tremor the key to reproducing inverse linear spectral decay is that the slip pulse has a constant mean moment rate this model provides new insights into the physical source process of lfes and tremor and should find practical use in assessing properties of deep plate interfaces

variations of fluid pressure within the subducting oceanic crust and slow earthquakes 1 we show fine scale variations of seismic velocities and converted teleseismic waves that reveal the presence of zones of high pressure fluids released by progressive metamorphic dehydration reactions in the subducting philippine sea plate in tokai district japan these zones have a strong correlation with the distribution of slow earthquakes including long term slow slip ltss and low frequency earthquakes lfes overpressured fluids in the ltss region appear to be trapped within the oceanic crust by an impermeable cap rock in the fore arc and impede intraslab earthquakes therein in contrast fluid pressures are reduced in the lfe zone which is deeper than the centroid of the ltss because there fluids are able to infiltrate into the narrow corner of the mantle wedge leading to mantle serpentinization the combination of fluids released from the subducting oceanic crust with heterogeneous fluid transport properties in the hanging wall generates variations of fluid pressures along the downgoing plate boundary which in turn control the occurrence of slow earthquakes

spatiotemporal distribution of seismic energy radiation from low frequency tremor in western shikoku japan 1 the spatiotemporal patterns of the radiated seismic energy from low frequency tremor associated with slow slip events in western shikoku japan have been estimated a spatially decaying mean square amplitude and differential traveltime measurement from envelope correlations observed at hi net stations were used to locate tremors and to estimate their seismic energies tremor amplitude was corrected for the site amplification factors estimated using the coda normalization method the location of the tremor is estimated as the position where both the decay of the observed energy and the differential travel times are well explained the temporal pattern of the total energy released agrees very well with the observed tilt records although the spatial patterns of the energy radiation vary strongly among the six slow slip events sses in western shikoku the region where they overlap always radiates relatively high levels of energy the estimated band limited energy rate of the tremor for a 2 to 10 hz bandwidth was typically between 105 and 106 j min though there is temporal variation of the radiation energy the released total energy associated with the sses whose magnitude is 5 9 6 1 is on the order of 108 j within the duration of sses of 8 13 days this is quite small energy radiation compared to the moment release of accompanying sse the scaled energy which is the ratio of the seismic moment and the seismic energy for the slow slip and a very low frequency earthquake was estimated to be 5 orders of magnitude smaller than that of a regular earthquake

plagioclase preferred orientation in layered mylonites evaluation of flow laws for the lower crust thesis s m joint program in marine geology and geophysics massachusetts institute of technology dept of earth atmospheric and planetary sciences and the woods hole oceanographic institution 2008

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

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

neogene aquifer properties specified through the interpretation of electrical sounding data salamiyeh region central syria twenty nine schlumberger electrical soundings were carried out in the salamiyeh region in syria using a maximum current electrode separation of 1 km three soundings were made at existing boreholes for comparison aquifer parameters of hydraulic conductivity and transmissivity were obtained by analysing pumping test data from the existing boreholes an empirical relationship between hydraulic conductivity determined from the pumping test and both resistivity and thickness of the neogene aquifer has been established for these boreholes in order to calculate the geophysical hydraulic conductivity a close agreement has been obtained between the computed hydraulic conductivity and that determined from the pumping test the relationship established has therefore been generalized in the study area in order to evaluate hydraulic conductivity and transmissivity at all the points where geoelectrical measurements have been carried out this generalization allows one to derive maps of the hydraulic conductivity and transmissivity in the study area based on geoelectrical measurements these maps are important in future modelling processes oriented towards better exploitation of the aquifers copyright 2006 john wiley sons ltd

migration properties of non volcanic tremor in shikoku southwest japan 1 based on the precise locations of deep non volcanic tremor in southwest japan which show a depth dependent behavior we clarified characteristic properties of tremor migration major tremor swarms are mainly initiated at deep levels of the tremor zone corresponding to areas of frequent minor tremor and migrate up dip along the subduction interface in central and eastern shikoku tremor occurs in two clusters separated by a small gap with the timing of tremor activity in the clusters differing by 1 or 2 days the time evolution of tremor activity in western shikoku reveals that the migration front of tremor propagates continuously and radially even in the case of a tremor gap these findings indicate that the rupture front of slow slip events propagates continuously and radially from the deep levels through the area without tremor activity the occurrence of tremor may depend on the existence of inhomogeneous patches upon the plate interface

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

space time correlation of slip and tremor during the 2009 cascadia slow slip event 1 episodic tremor and slip ets involving transient deformations accompanied by emergent low frequency tremor occurs in subduction zones around the world ets events increase the shear stress on locked megathrusts and may potentially trigger damaging earthquakes despite the clear association of tremor and slip the physical relationship between them is unresolved tremor appears to result from slip on small asperities on the plate interface due to either creep on the surrounding fault or stress increases ahead of the propagating slow slip front previous studies of migrating slow slip events have not had sufficient spatial and temporal resolution to differentiate between these two models to address this we invert gps data from the august 2009 ets event in central cascadia for the space time evolution of fault slip rate we find a correlation in both space and time between tremor epicenters and the independently determined position of high fault slip rate this supports the first hypothesis that tremor asperities are loaded directly by slow slip rather than by stress increases ahead of the slip front and provides new insights into the mechanics of ets

enhanced detection capability of non volcanic tremor using a 3 level vertical seismic array network va net in southwest japan 1 this study evaluates a method that enhances detection of non volcanic low frequency tremor nvt using va net a 3 level vertical seismic array network that was recently constructed in southwest japan the method employs semblance analysis for continuous vertical array records and calculates semblance coefficients as a function of time and apparent vertical velocity the sign of the best apparent velocity provides information about propagation direction either upward or downward allowing easy discrimination between seismic signals of natural origin and unwanted noise such as man made vibrations we applied the method to a nvt episode that occurred beneath the kii peninsula during november 2008 to demonstrate that nvt signals can be detected using only the 3 level array furthermore we demonstrate that the method enables us to detect minor nvt activity which is not detected by a conventional envelope cross correlation method resulting in a dramatic improvement in detection capability