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

a continuum of stress strength and slip in the cascadia subduction zone movement of the down going oceanic plate in subduction zones is accommodated by earthquakes slow slip and free slip with increasing depth analysis of accompanying tremor reveals a continuum of slow slip events in the cascadia subduction zone which suggests that deep free slip of the subducted plate may cause stress to be gradually transferred up the plate interface towards the seismogenic zone

determination of focal mechanisms of nonvolcanic tremor using s wave polarization data corrected for the effects of anisotropy we propose a method to determine the focal mechanisms of nonvolcanic tremors using anisotropy corrected s polarizations measured directly from noisy tremor signals the successful retrieval of polarization angles in noisy signals owes much to the observation that in general tremors propagate slowly and therefore do not change their location immediately this feature of tremors enables us to use longer time windows to compute polarization angles e g 1 min or longer resulting in a stack of particle motions we applied the method to a tremor episode that occurred beneath the kii peninsula in april 2013 although the majority of inferred focal mechanisms suggested that tremors manifest shear slip on the plate interface some events with strike slip components were also found to have occurred the proposed method provides us with a tool for investigating smaller scale spatial distributions and temporal variations of focal mechanisms throughout tremor zones

evidence of earthquake triggering by the solid earth tides article i nfo clearevidence forearthquake triggeringbythe earth tides hasremained elusive for morethan a century using the largest global earthquake catalog available the neic catalog with 442412 events we observe a clear correlation with 99 confidence between the phase of the solid earth tide and the timing of seismic events earthquakes occur slightly more often at the time of ground uplift by the earth tide i e when normal stresses are reduced within the lithosphere we observe that this phase distribution anomaly is larger for smaller and shallowerearthquakes although earthquakes inregionswithdominantlynormalandstrike slip faulting seem to exhibit more tidal triggering than regions dominated by thrust faulting there is no statistically significant evidence for a focal mechanism dependence on earthquake triggering finally we show here that it is highly probablethat the observedtriggeringiscaused bythe solid earth tide ratherthan byloading fromthe oceanor atmospheric tides although an additional impact due to loading from ocean tides is possible and probable we cannot detect it here because the earthquake database is not sufficiently complete and homogeneous more smallmagnitudeearthquakesinoceanicareasareneeded ourresultsareconsistentwiththeideaofadamped

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

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

megathrust earthquake swarms indicate frictional changes which delimit large earthquake ruptures abstract using a recently constructed catalog of megathrust earthquake swarms we present results that illustrate how fault slip for m w 8 5 earthquakes with a publicly available finite fault rupture model is delimited along strike by swarm regions we further investigate this relationship for all m w 7 5 subduction zone megathrust earthquakes that have occurred over the last 40 years by estimating the rupture area from early aftershocks this extended comparison shows only 2 out of 42 earthquakes propagate through regions of the megathrust that have documented recurring earthquake swarm activity while about 40 17 out of 42 are terminate on at least one side near regions with swarm activity in japan chile sumatra and alaska earthquake swarms correlate with regions of the plate interface that exhibit low interseismic strain accumulation this suggests earthquake swarms are associated with reduced plate coupling and possibly aseismic moment release however earthquakes in chile and alaska ruptured through regions of weak coupling that do not show swarm activity we propose instead that stress heterogeneity on the megathrust can best explain why large earthquake ruptures terminate in swarm regions but not in regions with weak coupling alone earthquake swarms appear to be a proxy for along strike segmentation of subduction megathrusts at least on the time scale of one seismic cycle

multiscale brittle ductile coupling and genesis of slow earthquakes we present the first attempt to explain slow earthquakes as cascading thermal mechanical instabilities to attain this goal we investigate brittle ductile coupled thermal mechanical simulation on vastly different time scales the largest scale model consists of a cross section of a randomly perturbed elasto visco plastic continental lithosphere on the order of 100 9 100 km scale with no other initial structures the smallest scale model investigates a km scale subsection of the large model and has a local resolution of 40 9 40 m the model is subject to a constant extension velocity applied on either side we assume a free top surface and with a zero tangential stress along the other boundaries extension is driven by velocity boundary conditions of 1 cm a applied on either side of the model this is the simplest boundary condition and makes it an ideal starting point for understanding the behavior of a natural system with multiscale brittle ductile coupling localization feedback is observed as faulting in the brittle upper crust and ductile shearing in an elasto viscoplastic lower crust in this process brittle faulting may rupture at seismogenic rates e g at 10 2 10 3 ms 1 whereas viscous shear zones propagate at much slower rates up to 3 9 10 9 ms 1 this sharp contrast in the strain rates leads to complex short time scale interactions at the brittle ductile transition we exploit the multiscale capabilities from our new simulations for understanding the underlying thermo mechanics spanning vastly different time and length scales

seismic wave attenuation determined from tectonic tremor in multiple subduction zones abstract tectonic tremor provides a new source of observations that can be used to constrain the seismic attenuation parameter for ground motion prediction and hazard mapping traditionally recorded earthquakes of magnitude 3 8 are used to develop ground motion prediction equations however typical earthquake records may be sparse in areas of high hazard in this study we constrain the distance decay of seismic waves using measurements of the amplitude decay of tectonic tremor which is plentiful in some regions tectonic tremor occurs in the frequency band of interest for ground motion prediction i e 2 8 hz and is located on the subducting plate interface at the lower boundary of where future large earthquakes are expected we empirically fit the distance decay of peak ground velocity from tremor to determine the attenuation parameter in four subduction zones nankai japan cascadia united states canada jalisco mexico and southern chile with the large amount of data available from tremor we show that in the upper plate the lower crust is less attenuating than the upper crust we apply the same analysis to intraslab events in nankai and show the possibility that waves traveling from deeper intraslab events experience more attenuation than those from the shallower tremor due to ray paths that pass through the subducting and highly attenuating oceanic crust this suggests that high pore fluid pressure is present in the tremor source region these differences imply that the attenuation parameter determined from intraslab earthquakes may underestimate ground motion for future large earthquakes on the plate interface

measurements of the strain field associated with episodic creep events on the san andreas fault at san juan bautista california over the past 6 years repeated strain steps recorded on a tensor strainmeter installed close to the san andreas fault trace at san juan bautista in california correlated closely with episodic creep events registered on a nearby creepmeter the strain events were remarkably similar in character were of about 1 hour duration and were followed within hours to days by creep events of 2 6 days duration the episodic slip of a source region from 200 m to 500 m in depth and at most a few kilometers in length is consistent with the observed strain and creep data we postulate that the additional stress transferred to this region by the loma prieta earthquake is giving rise to an increased rate of accumulation of shear strain around a locked patch beneath the creep source region thus accounting for the increased frequency of the creep strain events following the loma prieta earthquake

a large silent earthquake in the guerrero seismic gap mexico 1 geodetic measurements from a network of permanent gps stations along the pacific coast of mexico reveal a large silent earthquake along the segment of the cocos north american plate interface identified as the guerrero seismic gap the event began in october of 2001 and lasted for 6 7 months average slip of 10 cm produced measurable displacements over an area of 550 250 km2 the equivalent moment magnitude of the event was mw 7 5 recognition of this and previous slow event here indicate that the seismogenic portion of the plate interface is not loading steadily as hitherto believed but is rather partitioning the stress buildup with episodic as opposed to steady state or periodic slip downdip of the seismogenic zone this process increases the stress at the base of the seismogenic zone bringing it closer to failure these results call for a reassessment of the seismic potential of guerrero and other seismic gaps in mexico

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

earthquake spectra and near source attenuation in the cascadia subduction zone f 1 for slow events and as f 2 for fast earthquakes we show that at least in cascadia wave propagation effects likely control spectral decay rates above 2 hz we use seismograms from multiple small aperture arrays to estimate the spectral decay rates of near source spectra of 37 small events and find strong correlation between source location and decay rate the decay rates 1 vary overall by an amount in excess of that inferred to distinguish slow sources from fast earthquakes 2 are indistinguishable for sources separated by a few tens of km or less and 3 separate into two populations that correlate with propagation through and outside a low velocity zone imaged tomographically we find that some events repeat as is characteristic of low frequency earthquakes lfes but have spectra similar to those of non repeating earthquakes we also find no correlation between spectral decay rates and rates of ambient tremor activity these results suggest that earthquakes near the plate boundary at least in cascadia do not distinctly separate into slow and fast classes and correctly accounting for propagation effects is necessary to characterize sources

a slow earthquake sequence on the san andreas fault earthquakes typically release stored strain energy on timescales of the order of seconds limited by the velocity of sound in rock over the past 20 years observations1 13 and laboratory experiments14 have indicated that rupture can also occur more slowly with durations up to hours such events may be important in earthquake nucleation15 and in accounting for the excess of plate convergence over seismic slip in subduction zones the detection of events with larger timescales requires near field deformation measurements in december 1992 two borehole strainmeters close to the san andreas fault in california recorded a slow strain event of about a week in duration and we show here that the strain changes were produced by a slow earthquake sequence equivalent magnitude 4 8 with complexity similar to that of regular earthquakes the largest earthquakes associated with these slow events were small local magnitude 3 7 and contributed negligible strain release the importance of slow earthquakes in the seismogenic process remains an open question but these observations extend the observed timescale for slow events by two orders of magnitude

on corner frequencies attenuation and low frequency earthquakes we have recently suggested that the nearly constant duration of low frequency earthquakes lfes and equivalently the band limitation of tectonic tremor manifests a moment duration scaling that is fundamentally different from regular earthquakes and is most easily explained as rupture on asperities of roughly constant dimension in that work we employed qualitative arguments against potential bias by attenuation here we examine the role of attenuation more quantitatively through an analysis that avoids specification of particular source e g brune models and relies on the particle velocity spectral maximum as the definition of apparent corner frequency the analysis leads to the formal definition of a saturation frequency as the limiting value of apparent corner frequency as the true corner frequency tends infinity the saturation frequency a formal equivalent to fmax can be used to set bounds on path averaged quality factor q we apply these relations to deep crustal and intraslab earthquakes beneath vancouver island to estimate bulk crustal attenuation parameters that are subsequently used to correct apparent corner frequency measurements of lfes reported in our earlier work the attenuation bias due to bulk crustal structure is shown to be small with negligible effect on the principal conclusions of that study however a review of laboratory and seismic refraction measurements of attenuation in oceanic basalts and evidence for high p to s lfe corner frequency ratios raises the possibility that strong highly localized near source attenuation accompanying high pore fluid pressures could cause the bandlimited nature of lfes through the depletion of high frequencies

very low frequency earthquakes within accretionary prisms are very low stress drop earthquakes 1 we report characteristic p wave spectra and stress drops of very low frequency vlf earthquakes that occurred within the accretionary prism along the nankai trough southwestern japan although many vlf earthquakes showed no distinct phases on a raw seismogram a few showed slightly distinct phases the arrival times of some phases were consistent with the calculated p wave arrival times the corner frequencies of the vlf earthquakes were calculated using the stacked p wave spectra assuming an omega square spectrum stress drops were very low i e in the range of 0 1 10 kpa which corresponds to 0 1 1 of those of ordinary earthquakes such extremely low stress drops of the vlf earthquakes suggest that the fault strength within the accretionary prism may have weakened due to the existence of a fluid within the thrust fault system of the accretionary prism

a fault model of the 1946 nankaido earthquake derived from tsunami data abstract a fault model of the 1946 nankaido earthquake m 8 2 is determined by the use of tsunami records of uwajima shimotsu and hososhima which were located within or near the area of major coseismic crustal deformation synthetic tsunamis computed for various fault models are matched with the observed tsunamis to determine the fault parameters a low angle thrust model slightly revised from a previous model by ando is consistent with the observed tsunamis the duration of faulting is constrained as less than 10 min based upon the tsunami the fault is divided into an eastern and a western segment corresponding to areas associated with and without aftershocks respectively the fault area and dislocation for the western segment are 150 70 km2 and 6 m and those for the eastern segment are 150 70 km2 and 3 m respectively the total seismic moment is 4 7 1028 dyn cm significantly smaller than that obtained from a geodetic model by fitch and scholz but still larger than that of the seismic model by kanamori the discrepancy in seismic moment between the seismic and the present models ran2 could be interpreted in terms of a slow dislocation on the fault but this interpretation does not match the seismic intensity distribution and damage pattern and the slow slip model for the nankaido earthquake is rejected the discrepancy between the two seismic moments is considered insignificant within error involved in data and modeling assumptions if the revised geodetic model ran2 is modified the seismic moment required to explain the observed tsunamis would be reduced further by 30 if we consider the uncertainties involved in the fault model of kanamori and the fault finiteness effect affecting the amplitude of seismic waves the seismic moment required to interpret the seismic wave data could be increased possibly being more than twice that of kanamori thus the two seismic moments from the different data sets could be close to each other within allowable tolerance this implies that the rise time of the nankaido earthquake was short enough to generate short period seismic waves from both the western and the eastern fault segments

coseismic slip of the 2010 mw 8 8 great maule chile earthquake quantified by the inversion of grace observations abstract the 27 february 2010 mw 8 8 maule chile earthquake ruptured over 500 km along a mature seismic gap between 34 s and 38 s the concepcion constitucion gap where no large megathrust earthquakes had occurred since the 1835 mw 8 5 event notable discrepancies exist in slip distribution and moment magnitude estimated by various models inverted using traditional observations such as teleseismic networks coastal river markers tsunami sensors global positioning system gps and interferometric synthetic aperture radar insar we conduct a spatio spectral localization analysis based on slepian basis functions of data from gravity recovery and climate experiment grace to extract coseismic gravity change signals of the maule earthquake with improved spatial resolution 350 km half wavelength our results reveal discernible differences in the average slip between the grace observation and predictions from various coseismic models the sensitivity analysis reveals that grace observation is sensitive to the size of the fault but unable to separate depth and slip here we assume the depth of the fault is known and simultaneously invert for the fault plane area and the average slip using the simulated annealing algorithm our grace inverted fault plane length and width are 429 6 km 146 5 km respectively the estimated slip is 8 1 1 2 m indicating that most of the strain accumulated since 1835 in the concepcion constitucion gap was released by the 2010 maule earthquake

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

a slow thrust slip event following the two 1996 hyuganada earthquakes beneath the bungo channel southwest japan we report a slow thrust slip event that occurred beneath the bungo channel region southwestern japan on oct and dec 1996 two hyuganada earthquakes both mw 6 7 followed by afterslips occurred in addition a crustal movement characterized by an extremely slow rise was observed around the bungo channel about 200 km north from the epicenters and continued for about 300 days long assuming a slow slip on the plate boundary we estimate its duration and surface displacements from gps time series data by curve fitting and then determine the fault slip distribution we found that a slow slip without any earthquakes continued for nearly one year and released the seismic moment comparable to that of the hyuganada earthquakes occurrence of the slow thrust slip event suggests that this kind of event may be a characteristic mode of stress release at a transition region of interplate coupling

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

detection and monitoring of ongoing aseismic slip in the tokai region central japan analysis of global positioning system data shows that the rate of crustal deformations in the tokai region of japan a seismic gap area changed over the past 18 months kalman filtering analysis shows aseismic slip on the plate boundary in the western tokai region centered on lake hamana adjacent to the anticipated tokai earthquake source area the cumulative moment magnitude reaches 6 7 in june 2002 with a relative slip increase northeast of lake haman from january 2002 an existence of aseismic slip in the western tokai supports the hypothesis of a silent event as the cause of uplifting several days before the 1944 tonankai earthquake

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

constraints on slow earthquake dynamics from a swarm in central italy several clustered slow earthquakes have been recorded by a geodetic interferometer in central italy the strain rise times of the events range from tens to thousands of seconds and the seismic moment scales with the square root of the rise time this scaling law contrasts with the conservative assumption of constant rupture velocity in fault modeling but is consistent with the occurrence of a slow rupture propagation analogous to heat diffusion in a slab

slow slip event in the mexican subduction zone evidence of shallower slip in the guerrero seismic gap for the 2006 event revealed by the joint inversion of insar and gps data slow slip events sses in subduction zones have been observed in the last decade with continuous gps stations some of them could be related to the lateral segmentation of subduction interface that seems to be a critical parameter for the propagation of large subduction earthquakes in 2006 one of the largest sses recorded so far was captured by a dozen continuous gps stations in the guerrero area mexico along the mexican subduction zone previous studies based on these data suggested a lateral variation of the updip depth of the see at the guerrero seismic gap but suffered from a lack of resolution east of the gap here we show the ability of insar technique to capture a part of the 2006 sse cumulative displacement east of the guerrero gap by a stacking approach we processed long strip envisat interferograms corrected for orbital errors and interseismic signal using gps data we first use a forward modelling approach to test insar sensitivity to the amount of slip depth and width of the slipping area on the subduction interface due to its high spatial resolution insar allows one to comprehensively sample the north south spatial wavelength of the sse deformation complementing the sparse gps network insar locates the maximum of uplift and subsidence caused by the sse more precisely than the gps data giving better constraints on the updip slip limit of the sse we then inverted the insar and gps data separately to understand how each inversion resolves the slip at depth finally we performed a joint inversion of insar and gps data which constrained the sse slip and its location on the plate interface over the entire guerrero area the joint inversion shows significant lateral variation of the sse slip distribution along the trench with a shallower updip edge in the guerrero seismic gap west of acapulco and a deeper slip edge further east

earthquake swarms in circum pacific subduction zones abstract we systematically and manually search through clusters of earthquakes along circum pacific subduction zones to identify potential earthquake swarms in total we find 266 potential earthquake swarms 180 we classify as megathrust and 68 we classify as volcanic due to their proximity to the megathrust or to volcanoes we focus on the megathrust swarms and demonstrate that 1 the number of events in a swarm is not a function of the largest earthquake in the swarm 2 swarms exhibit an approximately constant rate of seismicity that lasts until after the mean timing of events in the swarm 3 the timing of the largest earthquake in the sequence is no different than the timing of any other earthquake in the sequence 4 our catalogs of earthquakes comprising swarms 9000 events have high b values 1 5 to 2 and 5 when earthquake swarms are considered as single events using total duration and cumulative moment they appear to be consistent with the slow earthquake magnitude duration scaling law presented by ide et al 2007 the first three observations along with the observation that swarms can span very large areas compared to their cumulative seismic moment argue against static stress triggering as a driving mechanism for earthquake swarms along strike propagation velocities are observed for several swarms showing epicentral propagation of 10 km day similar to other documented slow slip events together this evidence implies that aseismic slip along the megathrust is likely an important mechanism for the generation of megathrust earthquake swarms in circum pacific subduction zones we then conduct a comparison of swarms and large megathrust earthquakes finding evidence that the two are broadly anti correlated megathrust segments with large earthquake swarm gaps are more likely to experience large mw 8 megathrust events we characterize the ubiquity of megathrust swarms at different margins and suggest that fault properties along marianas type margins may allow for earthquake swarms to occur regularly but other margins may rely on other variables such as the subduction of a ridge or seamount to facilitate the generation of megathrust earthquake swarms

hunt for slow slip events along the sumatran subduction zone in a decade of continuous gps data 10 pages 4 figures supporting information http dx doi org 10 1002 2015jb012503 this work is earth observatory of singapore paper number 104

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

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

integration of transient strain events with models of plate coupling and areas of great earthquakes in southwest japan we model the crustal deformation caused by two long term subduction slip transients in southwest japan which we refer to as the 2000 2004 tokai and the 2002 2004 bungo channel slow slip events sses we use re analysed geonet position time series and a kalman filter based network inversion method to image the spatiotemporal slip variation of the two events on the plate interface during the period of 1998 2004 67 and 2000 2005 both events are found to have complex slip histories with multiple subevents in addition to a newly identified slip subevent in 2002 2003 we find that the major event in the bungo channel sse initiated in early 2003 beneath the northeastern corner of the region and expanded southwestward in contrast to the slip characteristics suggested by other studies the re analysed gps data in the tokai region shows a renewed slip activity for the tokai sse in early 2003 2004 at a similar location as in the period of 2001 2002 the equivalent m w for both the tokai and bungo channel sses are about 7 0 our results show that the tokai sse appears to start before the miyaki kozu seismovolcanic event integrating plate coupling and sses shows that the transient slip zones are located in a region between the locked zones and the epicentres of the low frequency earthquakes lfes at least part of the interseismic slip deficit is released by episodic sses beneath the bungo channel region we find excellent temporal correspondence between transient slip and adjacent lfes for both sse suggesting that they are closely related and possibly reflect that long term slow slip may modulate the occurrence of lfes

slow rupture of an aseismic fault in a seismogenic region of central italy 1 slow earthquakes and afterslips prove that the earth does not have just two response time scales i e that of tectonic loading and that of regular earthquakes a swarm of slow earthquakes with time constants of the order of hundreds of seconds has been detected by a laser interferometer below the gran sasso massif italy we analyse and model these observations to identify a very plausible source in a local fault with no historic seismic behavior while slow earthquakes occurring in subduction zones and at the transition between locked and stably sliding segments of the san andreas fault are often associated with seismic events in the case of the apennines there is no correlation between local seismicity and slow earthquakes slow earthquakes therefore may also represent a specific failure behavior for a seismically locked fault adding further complexity to the interpretation of geologic data for seismic hazard estimates

erosion and sedimentation in kalpakkam n tamil nadu india from the 26th december 2004 tsunami abstract laterally extensive sand sheets deposited by the 26th december 2004 asian tsunami provide a valuable modern analogue for comparison with wash over deposits of unknown origin in many places on the east coast of india distinct deposits of marine sand drape the landscape and overlie the muddy soils of the coastal plain this paper discusses detailed measurements of coastal topography tsunami flow height and deposit thickness made at kalpakkam india five transects were examined in detail to assess the sedimentology and spatial distribution of the tsunami deposit near the mean water line the tsunami eroded approximately 10 25 cm of sand from the beach and berm at kalpakkam the sand sheet deposited by the tsunami begins 25 m from the shore extending 420 m inland where it becomes thin and patchy approximately 30 m from the limit of inundation in some cases the deposit consists of 2 to 4 normally graded units with coarse sand near the base and fine sand at the top a characteristic observed in many tsunami deposits worldwide in many places the deposits also contain numerous thin laminated units a characteristic usually associated with storm over wash the presence of the laminated beds is indicative of the complexity of tsunami sedimentation on the coast such observations are essential to the formation of definitive facies models for palaeo overwash studies that are capable of distinguishing between sediments deposited by storms or tsunami

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

bridging great earthquake doublets through silent slip on and off fault aftershocks of the 2006 kuril island subduction earthquake toggled by a slow slip on the outer rise normal fault of the 2007 great earthquake 1 the november 2006 great thrust earthquake of moment magnitude m w 8 3 on the plate boundary in the kuril chishima islands triggered as many vigorous normal faulting aftershocks in the outer rise region seaward of the trench as on fault aftershocks here we show that the aftershocks for a 40 day period preceding the january 2007 m w 8 1 event in the outer rise were less frequently observed than the rate expected by both the omori utsu formula and the epidemic type aftershock sequence etas model while at the same time were more frequent along the plate boundary we discuss whether such simultaneous quiescence and activation in the pervasive 2006 aftershocks might have been initiated by the onset of aseismic slip on the 2007 rupture plane the stable fault sliding in an elastic half space demonstrates progressive stress shadowing in the outer rise and stress loading along the plate boundary furthermore the rate and state dependent friction of dieterich quantitatively simulates temporal changes in seismic behavior the same trends of the anomalous activities last in both zones after the 2007 rupture which suggests that the slips continuously take place in the similar region on the fault throughout the period before and after the rupture the kuril case implies that temporal seismic quiescence in an aftershock sequence is useful in evaluating the possibility of the subsequent triggered event thus suggesting itself as a potential earthquake forecasting model together with pervasive earthquake clustering models

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

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

an efficient implicit explicit adaptive time stepping scheme for multiple time scale problems in shear zone development 1 problems associated with shear zone development in the lithosphere involve features of widely different time scales since the gradual buildup of stress leads to rapid and localized shear instability these phenomena have a large stiffness in time domain and cannot be solved efficiently by a single time integration scheme this conundrum has forced us to use an adaptive time stepping scheme in particular the adaptive time stepping scheme ats where the former is adopted for stages of quasi static deformation and the latter for stages involving short time scale nonlinear feedback to test the efficiency of this adaptive scheme we compared it with implicit and explicit schemes for two different cases involving 1 shear localization around the predefined notched zone and 2 asymmetric shear instability from a sharp elastic heterogeneity the ats resulted in a stronger localization of shear zone than the other two schemes we report that usual implicit time step strategy cannot properly simulate the shear heating due to a large discrepancy between rates of overall deformation and instability propagation around the shear zone our comparative study shows that while the overall patterns of the ats are similar to those of a single time stepping method a finer temperature profile with greater magnitude can be obtained with the ats the ability to model an accurate temperature distribution around the shear zone may have important implications for more precise timing of shear rupturing

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

extended nucleation of the 1999 mw 7 6 izmit earthquake laboratory and theoretical studies suggest that earthquakes are preceded by a phase of developing slip instability in which the fault slips slowly before accelerating to dynamic rupture we report here that one of the best recorded large earthquakes to date the 1999 moment magnitude mw 7 6 izmit turkey earthquake was preceded by a seismic signal of long duration that originated from the hypocenter the signal consisted of a succession of repetitive seismic bursts accelerating with time and increased low frequency seismic noise these observations show that the earthquake was preceded for 44 minutes by a phase of slow slip occurring at the base of the brittle crust this slip accelerated slowly initially and then rapidly accelerated in the 2 minutes preceding the earthquake

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

earthquakes triggered by silent slip events on kīlauea volcano hawaii silent earthquakes or slow slip events happen so slowly that they cannot be detected by conventional seismographs but now the availability of gps data means that they can be followed in detail segall et al report on a series of small earthquakes on k lauea volcano hawaii the earthquakes at depths of 7 to 8 km appear to be triggered by otherwise silent slow slips though small triggered earthquakes of this type can be used to help quantify the increased hazard due to slow slip events slow slip events or silent earthquakes have recently been discovered in a number of subduction zones including the nankai trough1 2 3 in japan cascadia4 5 and guerrero6 in mexico but the depths of these events have been difficult to determine from surface deformation measurements although it is assumed that these silent earthquakes are located along the plate megathrust this has not been proved slow slip in some subduction zones is associated with non volcanic tremor7 8 but tremor is difficult to locate and may be distributed over a broad depth range9 except for some events on the san andreas fault10 slow slip events have not yet been associated with high frequency earthquakes which are easily located here we report on swarms of high frequency earthquakes that accompany otherwise silent slips on k lauea volcano hawaii for the most energetic event in january 2005 the slow slip began before the increase in seismicity the temporal evolution of earthquakes is well explained by increased stressing caused by slow slip implying that the earthquakes are triggered the earthquakes located at depths of 7 8 km constrain the slow slip to be at comparable depths because they must fall in zones of positive coulomb stress change triggered earthquakes accompanying slow slip events elsewhere might go undetected if background seismicity rates are low detection of such events would help constrain the depth of slow slip and could lead to a method for quantifying the increased hazard during slow slip events because triggered events have the potential to grow into destructive earthquakes

low frequency earthquakes observed in close vicinity of repeating earthquakes in the brittle upper crust of hakodate hokkaido northern japan we conducted a detailed investigation of an earthquake cluster distributed from the lower crust to the upper crust beneath hakodate hokkaido which included both low frequency earthquakes lfes a

an autocorrelation method to detect low frequency earthquakes within tremor 1 recent studies have shown that deep tremor in the nankai trough under western shikoku consists of a swarm of low frequency earthquakes lfes that occur as slow shear slip on the down dip extension of the primary seismogenic zone of the plate interface the similarity of tremor in other locations suggests a similar mechanism but the absence of cataloged low frequency earthquakes prevents a similar analysis in this study we develop a method for identifying lfes within tremor the method employs a matched filter algorithm similar to the technique used to infer that tremor in parts of shikoku is comprised of lfes however in this case we do not assume the origin times or locations of any lfes a priori we search for lfes using the running autocorrelation of tremor waveforms for 6 hi net stations in the vicinity of the tremor source time lags showing strong similarity in the autocorrelation represent either repeats or near repeats of lfes within the tremor we test the method on an hour of hi net recordings of tremor and demonstrates that it extracts both known and previously unidentified lfes once identified we cross correlate waveforms to measure relative arrival times and locate the lfes the results are able to explain most of the tremor as a swarm of lfes and the locations of newly identified events appear to fill a gap in the spatial distribution of known lfes this method should allow us to extend the analysis of shelly et al 2007a to parts of the nankai trough in shikoku that have sparse lfe coverage and may also allow us to extend our analysis to other regions that experience deep tremor but where lfes have not yet been identified

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

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

coseismic slip resolution along a plate boundary megathrust the nankai trough southwest japan geodetic survey measurements are used to estimate the coseismic slip distribution in the 1944 tonankai mw 8 1 and 1946 nankaido mw 8 3 earthquakes and to assess quantitatively the degree to which this slip is resolved on the plate boundary megathrust data used include 798 angle changes from triangulation surveys 328 leveling section differences and 5 coseismic tidal gage offsets many of the nominally coseismic triangulation data span 50 years nearly half the earthquake cycle and correction for interseismic deformation using post 1950 observations is applied microseismicity is used to define the configuration of the plate boundary interface and approximate it with a continuous multisegment fault model because the onshore geodetic data have very limited resolving power for offshore fault segments offshore coseismic slip was constrained by satake s 1993 estimation based on tsunami data the majority of the coseismic slip occurs between 15 and 25 km depth although resolution declines toward the trench axis it is sufficiently good to define two distinct high slip regions one off southeastern shikoku island 11 m maximum and the other offshore of kii peninsula 3 m maximum the slip magnitude off southeastern shikoku coupled with the plate convergence rate would imply an recurrence interval of about 270 years much longer than the average repeat time of 120 years for historical great earthquakes on the nankai trough however the maximum coseismic slip is sensitive to the assumed fault geometry and slippage on trough parallel splay faults could significantly decrease the maximum slip to about 6 m

correcting high resolution borehole strainmeter data from complex external influences and partial solid coupling the case of trizonia rift of corinth greece high resolution borehole strainmeters are usually installed in tectonically active regions in order to detect slow slip events and to estimate slow transients related to earthquake swarms however they are also sensitive to other numerous influences internal or external furthermore the quality of their coupling to the rock through cementation and the mechanical properties of the rock mass around them have a critical influence on their records many of the existing strainmeters present such problems and the correction for these effects often remains a challenge in this paper we present the analysis of the records of a high resolution borehole dilatometer sacks evertson located in the seismically active rift of corinth greece station trz in the trizonia island we show that the instrument suffers from an only partial solid coupling and that the nearby sea tides have a direct through elastic response and indirect through pore pressure diffusion effect on the dilatation signal which adds up to the solid tidal strain source we propose a methodology that allows in a first step to better separate the internal solid tide from the external air pressure sea level influences by calculating a frequency dependent transfer function outside the range of the tidal periods we then extrapolate this function in particular at the tidal periods in a second step the resulting variation with frequency of the coupling coefficients with sea level led us to estimate the proportion of instrument not solidly cemented to rock thus in contact with water pore pressure which is about 90 of the total height despite the small proportion of solid coupling the sensor resolution remains very good up to a few tens of hours of a time period thanks to the confining effects of the rocks on the local pore pressure these results allow us to correct for the external effects and reduce the associated variance by 80 90 in the period range of minutes to days the empirical correction of the sea level effect could be explained using a simple boussinesq s approximation and 1d pore pressure diffusion model which contributed to better constraint of some of the poro elastic parameters in the vicinity of the instrument after correction the solid tidal signal at the 24 h period is almost anti correlated with those of the theoretical solid tide this surprising result is consistent with a similar anti correlation observed for the longest period surface waves 200 s comparing the trz dilatometer signals to the strain measured by a nearby borehole strainmeter mok 15 km this could be related to the presence of a shallow fault close to the instrument which would creep in response to seismic wave related stress

geodetic constraints on afterslip characteristics following the march 9 2011 sanriku oki earthquake japan 1 a magnitude 7 3 foreshock occurred at the subducting pacific plate interface on march 9 2011 51 h before the magnitude 9 0 tohoku earthquake off the pacific coast of japan we propose a coseismic and postseismic afterslip model of the magnitude 7 3 event based on a global positioning system network and ocean bottom pressure gauge sites the estimated coseismic slip and afterslip areas show complementary spatial distributions the afterslip distribution is located up dip of the coseismic slip for the foreshock and northward of hypocenter of the tohoku earthquake the slip amount for the afterslip is roughly consistent with that determined by repeating earthquake analysis carried out in a previous study the estimated moment release for the afterslip reached magnitude 6 8 even within a short time period of 51h a volumetric strainmeter time series also suggests that this event advanced with a rapid decay time constant compared with other typical large earthquakes

hydrocarbon inclusions in late calcite cements migration indicators in the great oolite group weald basin s england abstract the fluorescence responses of hydrocarbon inclusions in calcite and dolomite cements are used to indicate the timing and longevity of oil migration in great oolite reservoirs of the weald basin of southern england oil migration and late stage calcite cementation were penecontemporaneous processes the gravity of the included hydrocarbons increases towards the basin depocentre through the range of 20 to 40 api reflecting the maturity of the source rocks reservoirs with a spread in the gravity of oil within inclusions were charged throughout source rock maturation those reservoirs with oil inclusions of a single gravity were charged in a discrete event

similar scaling laws for earthquakes and cascadia slow slip events faults can slip not only episodically during earthquakes but also during transient aseismic slip events1 5 often called slow slip events previous studies based on observations compiled from various tectonic settings6 8 have suggested that the moment of slow slip events is proportional to their duration instead of following the duration cubed scaling found for earthquakes9 this finding has spurred efforts to unravel the cause of the difference in scaling6 10 14 thanks to a new catalogue of slow slip events on the cascadia megathrust based on the inversion of surface deformation measurements between 2007 and 201715 we find that a cubic moment duration scaling law is more likely like regular earthquakes slow slip events also have a moment that is proportional to a3 2 where a is the rupture area and obey the gutenberg richter relationship between frequency and magnitude finally these slow slip events show pulse like ruptures similar to seismic ruptures the scaling properties of slow slip events are thus strikingly similar to those of regular earthquakes suggesting that they are governed by similar dynamic properties a new catalogue of slow slip events on the cascadia megathrust shows that a cubic moment duration scaling law is likely with scaling properties strikingly similar to regular earthquakes

low frequency continuous tremor around the moho discontinuity away from volcanoes in the southwest japan 1 recent enhancement of seismic networks in the japan islands revealed occurrence of low frequency continuous tremors of a beltlike distribution in the southwest japan where the subducting philippine sea plate reaches depths of 30 40 km source depth of the tremor is estimated by selecting tremor segments with relatively clear p wave onsets the source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust mantle wedge and the subducting slab the long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor the most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments the northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water

newly observed deep slow slip events at the central hikurangi margin new zealand implications for downdip variability of slow slip and tremor and relationship to seismic structure 1 we present previously undocumented deep 25 45 km depth moderate duration 2 3 months slow slip events sses directly downdip of known shallow 15 km depth short term 2 3 weeks sses at the central hikurangi margin new zealand the moderate duration sses produce 2 6 mm of horizontal displacement at continuous global positioning system stations in 2006 and 2008 similar to cascadia sses they involve 2 5 cm of slip over 5000 km2 of the subduction interface tremor occurs just downdip of the deep sse source area we also present results from a large shallow 12 km sse in 2013 just updip of the 2006 2008 sses the location of deep sses between shallow short term sses and tremor indicates strong downdip variation of subduction interface slip behavior at central hikurangi the deep sses occur where qp and vp vs data suggest an accumulation of fluid rich underplated sediment at the interface consistent with the idea that sses occur under high fluid pressure

possible slip history scenarios for the hyuga nada region and bungo channel and their relationship with nankai earthquakes in southwest japan based on numerical simulations the nankai earthquakes are great interplate earthquakes with recurrence intervals of 100 200 years occurring along the nankai trough southwestern japan new geological evidences suggest that the rupture area of the 1707 earthquake one of the largest extended farther westward than previously thought and similar magnitude events may have recurrence intervals of several hundred years west of the nankai earthquake segments in the bungo channel region slow slip events sses have occurred with recurrence intervals of several years since 1980 farther westward no m 7 5 interplate earthquakes have occurred except for one in 1968 in the northern hyuga nada region near the bungo channel we numerically simulated the generation cycles of nankai earthquakes hyuga nada earthquakes and bungo channel sses to obtain possible slip histories in these regions particularly during 1707 1980 we showed that the nankai and hyuga nada earthquakes occur mostly independently with average recurrence intervals of 151 and 117 years respectively an sse patch slipped coseismically during both the nankai and hyuga nada earthquakes the rupture of the nankai earthquakes extended to the hyuga nada region every 500 600 years and was followed by quiescence of sses for more than 200 years subsequently sses occurred repeatedly every 8 years current observational findings are generally consistent with the characteristics obtained from our scenarios except regarding the recurrence intervals of hyuga nada earthquakes for which few observations are available further evidence of the slip history in these regions will be required to use information from such simulations to forecast future earthquakes

the geologic record of deep episodic tremor and slip transient and episodic slow slip accommodates a great deal of tectonic strain and may be mechanically linked with locked regions of seismically hazardous faults best documented in subduction zones and associated with nonvolcanic tremor most proposed mechanisms for slow slip revolve around the transition between stable and unstable frictional sliding the dilemma is that slow slip is generated at a wide range of crustal depths including at pressure temperature conditions where frictional deformation mechanisms give way to predominantly viscous ones we present a model for how fracture and viscous flow within mid crustal shear zones can produce episodic creep transients our model for such transients stems from geological examples of shear zones that formed at temperatures and pressures of 500 c and 0 6 gpa during early orogenesis following late cretaceous subduction of a backarc ocean basin within these shear zones relatively strong lenses of metabasalt localized fluid filled fractures that were subsequently deformed by viscous flow in surrounding quartzofeldspathic gneiss the spatial and temporal characteristics of the modeled creep events are similar to those of slow slip events observed in modern subduction zones we therefore suggest that some episodic tremor and slip can originate through combined fracture and viscous flow across shear zones comprising mixtures of strong and weak materials

seismicity controlled by a frictional afterslip during a small magnitude seismic sequence m l 5 on the chihshang fault taiwan we report evidence for frictional afterslip at shallow depths about 5 to 7 km during a small magnitude seismic sequence with ml 5 along the chihshang fault a main active structure of the longitudinal valley in southeast taiwan the afterslip which was recorded by a nearby borehole dilatometer lasted about a month with a cumulative geodetic moment magnitude of 4 8 0 2 the afterslip comprised two stages and controlled the aftershock sequence the first postseismic stage which followed a ml 4 6 earthquake lasted about 6 h and mostly controlled the ruptures of neighboring asperities e g multiplets near the hypocenter then a 4 week duration large afterslip event following a ml 4 9 earthquake controlled the rate of aftershocks during its first 2 days through brittle creep the study presents a rare case of simultaneous seismological and geodetic observations for afterslip following earthquakes with magnitude lower than 5 furthermore the geodetic moment of the postseismic phase is at least equivalent to the coseismic moment of the sequence

slow earthquake in afghanistan detected by insar 1 the chaman fault system forms a prominent 900 km long left lateral transform plate boundary between the indian and eurasian plates in afghanistan and pakistan here we show satellite radar interferometry data that revealed an afterslip or slow earthquake signal following an earthquake of magnitude 5 0 this slow slip episode lasted for more than a year and accompanied a widespread creep signal that occurred at least 50 km along the fault we detected no surface slip before the earthquake during the 1 5 years sampled by our data this finding of long lasting widespread afterslip demonstrates that the plate motion along the chaman fault is accommodated by slow slip episodes following moderate earthquakes and suggests that a potential for magnitude 7 class earthquakes was significantly reduced the duration and moment release of the detected afterslip do not fit the recently proposed scaling law for slow earthquakes

the slip distribution of the 1946 nankai earthquake estimated from tsunami inversion using a new plate model abstract a new model for the shape of the philippine sea plate psp subducting beneath southwest japan was constructed by combining marine seismic survey results and seismicity data this resulted in a plate model that is generally 3 5 km shallower than previous estimates and contains new details of plate boundary structure near the nankai trough axis we estimated the slip distribution of the 1946 nankai earthquake by inverting tsunami waveforms using the new plate boundary model and found that the large slip off cape muroto and seismic moment were reduced by about 10 from the previous estimate of tanioka and satake 2001a however we also found reason to suspect the tide gauge closest to the epicenter at shimotsu and this resulted in a much more substantial reduction in the amount of slip in the eastern segment of the rupture area we also find that our new rupture model correlates well with features of the subducting plate boundary such as a large subducting seamount off cape muroto kodaira et al 2000a this suggests that such features have an important effect on either earthquake rupture propagation or the interseismic accumulation of elastic strain energy or both

a generalization of the stochastic summation scheme of small earthquakes to simulate strong ground motions a generalization of the stochastic summation scheme of small earthquakes following a general form of the source spectrum n model is developed to estimate the proper probability density functions for rupture propagation over the fault and to simulate site specific strong ground motions in two independent stages the probability density functions for rupture propagation are first developed for a single corner frequency source model and then extended to multiplicative and additive double corner frequency source models to partially account for the effects of finite fault rupture such as fault geometry rise time and rupture time on ground motions and to better match observed fourier amplitude spectra fas the generalized two stage stochastic summation scheme developed in this study can be used to simulate realistic strong ground motion time histories from small events represented as empirical green s functions egfs by specifying only two source parameters of the seismic moment and stress drop for a given site the proposed two stage stochastic summation schemes are tested using numerical examples following the theoretical source models as well as observed ground motions of the 2011 mw 9 0 tohoku earthquake in japan and the 1994 mw 6 7 northridge earthquake in california to verify the applicability of the approach comparisons between the observed and simulated time histories for these two earthquakes their response spectra and fas show satisfactory performance of the proposed approach for engineering purposes the results of these comparisons indicate that the proposed stochastic summation of small events as egfs can adequately replicate observed ground motions and evaluate uncertainties in ground motions with the generation of many time history realizations corresponding to a multitude of possible rupture processes the proposed approach can also be used to generate multiple realistic acceleration time histories matched on average to the target response spectra for use in earthquake performance design and to develop ground motion models for low seismicity regions where there is a lack of recording of strong ground motions

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

spectrum of slip behaviour in tohoku fault zone samples at plate tectonic slip rates the tohoku earthquake ruptured a fault that also generates slow slip events laboratory experiments on rock samples from the fault show that this spectrum of slip behaviours is a natural consequence of shearing at slow plate convergence rates

slow slip events and time dependent variations in locking beneath lower cook inlet of the alaska aleutian subduction zone we identify a series of abrupt changes in gps site velocities in lower cook inlet alaska in late 2004 early 2010 and late 2011 the site motions during each time period are nearly linear the surface deformations inferred from gps for pre 2004 and 2010 2011 are similar to each other as are 2004 2010 and post 2011 we estimate the slip distribution on the alaska aleutian subduction plate interface accounting for upper plate block rotations and interpret this toggling between two deformation patterns as caused by transient slip we find that by allowing negative slip deficit rates i e creep rates in excess of relative plate motion the data in lower cook inlet are fit significantly better during pre 2004 and 2010 2011 suggesting the occurrence of slow slip events sses there during those time periods the earlier sse lasted at least 9 years observations in that area began in 1995 with mw 7 8 the latter sse had almost the same area as the earlier one and a duration of 2 years with mw 7 2 during 2004 2010 and post 2011 the inversions result in only positive slip deficit rates i e locking in lower cook inlet slip rates are nearly constant during the lower cook inlet sses and the events start and stop abruptly both of these properties contrast with observations of sses in upper cook inlet and elsewhere the lower cook inlet sses are consistent with previously proposed duration magnitude scaling laws and demonstrate that slow slip events can last as long as a decade

episodic slow slip events in the japan subduction zone before the 2011 tohoku oki earthquake abstract we describe two transient slow slip events that occurred before the 2011 tohoku oki earthquake the first transient crustal deformation which occurred over a period of a week in november 2008 was recorded simultaneously using ocean bottom pressure gauges and an on shore volumetric strainmeter this deformation has been interpreted as being an m6 8 episodic slow slip event the second had a duration exceeding 1 month and was observed in february 2011 just before the 2011 tohoku oki earthquake the moment magnitude of this event reached 7 0 the two events preceded interplate earthquakes of magnitudes m6 1 december 2008 and m7 3 march 9 2011 respectively the latter is the largest foreshock of the 2011 tohoku oki earthquake our findings indicate that these slow slip events induced increases in shear stress which in turn triggered the interplate earthquakes the slow slip event source area on the fault is also located within the downdip portion of the huge coseismic slip area of the 2011 earthquake this demonstrates episodic slow slip and seismic behavior occurring on the same portions of the megathrust fault suggesting that the faults undergo slip in slow slip events can also rupture seismically

influence of depth focal mechanism and tectonic setting on the shape and duration of earthquake source time functions source time functions of 255 moderate to great earthquakes obtained from inversions of teleseismic body waves by tanioka and ruff 1997 and coworkers were compared in a systematic way they were scaled to remove the effect of moment and to allow the direct comparison and averaging of time function shape as well as duration time function durations picked by tanioka and ruff 1997 are proportional to the cube root of seismic moment if moments from the harvard centroid moment tensor catalog are used the average duration of scaled time functions is shorter and the average shape has a more abrupt termination for deeper events than shallower ones with a distinct change occurring at 40 km depth the complexity of the time functions as quantified by the number of subevents appears to decrease below 40 km depth furthermore among events shallower than 40 km the average duration of scaled time functions is shorter and their average shape has a more abrupt termination 1 for events with strike slip focal mechanisms compared to thrust events and 2 for the few thrust events associated with an intraplate setting compared to the majority associated with an interplate subduction boundary in each of these cases events in more technically and seismically active settings have a longer duration and a more gradual termination this can be interpreted in terms of lower stress drops and or slower rupture velocities at active plate boundaries suggesting that fault rheology depends on slip rate and may evolve as total fault slip accumulates furthermore differences in average time function shape and duration associated with different subduction zones suggest that differences exist in the rheology on the plate boundaries at the various subduction zones supporting data table is available via web browser or via anonymous ftp from ftp kosmos agu org directory append username anonymous password guest subdirectories in the ftp site are arranged by paper number information on seraching and submitting electronic supplements is found at http www agu org pubs esupp about html

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

quantifying the time function of nonvolcanic tremor based on a stochastic model 1 nonvolcanic tremor is the seismically observable component of slow earthquakes which have been recently discovered in subduction zones around the world including major study areas at the nankai and cascadia subduction zones although tremor appears to occur randomly in both areas cascadia tremor has a longer duration than nankai tremor in the present study this difference in tremor duration is quantified using a brownian slow earthquake model that explains several features of tremor and slow earthquakes a previous brownian model is improved and applied to explain the cumulative distribution function of tremor amplitude which is approximated by a 2 distribution the model also shows that the power spectrum of tremor amplitude has a simple analytic formula including a characteristic time an inversion method is developed to measure the characteristic time from the tremor spectrum in the presence of non gaussian background noise the method is applied to several tremor sequences in the nankai and cascadia subduction zones to quantitatively confirm the apparent differences in tremor behavior between the two areas the constants for cascadia and nankai tremor are 1000 3000 s and 100 1000 s respectively with temporal increases in these values observed over the course of 1 day records of activity the difference in characteristic time between the two areas may reflect geometric constraints such as the width of the tremor region