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 comparison of in situ bottom pressure array measurements with grace estimates in the kuroshio extension 1 ocean bottom pressure estimates from gravity recovery and climate experiment grace have been validated by comparisons with an array of in situ bottom pressure measurements the 600 km by 600 km array comprised 46 bottom pressure sensors that were part of the kuroshio extension system study kess validations in other ocean regions have been limited by available data to pointwise bottom pressure measurements spatially averaged monthly mean bottom pressure over the kess array is highly correlated with grace bottom pressure estimated at the center of the array the correlations are nearly equally high for three standard choices of spatial smoothing radius applied to grace estimates 300 500 and 750 km in contrast pointwise comparisons between grace and individual bottom pressures are high or low in sub regions of kess depending partially upon the local variance of deep mesoscale eddies whose energetic length scales are shorter than 300 km kess is a suitable validation experiment for the grace estimates at monthly scales with 300 to 750 km spatial radius of smoothing

gps constraints on the 2011 2012 oaxaca slow slip event that preceded the 2012 march 20 ometepec earthquake southern mexico

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

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

coseismic slip distribution of the 2011 off the pacific coast of tohoku earthquake m9 0 refined by means of seafloor geodetic data 1 on 11 march 2011 the devastating m9 0 tohoku earthquake occurred on the interface of the subducting pacific plate and was followed by a huge tsunami that killed about 20 000 people several geophysical studies have already suggested that the very shallow portion of the plate interface might have played an important role in producing such a large earthquake and tsunami however the sparsity of seafloor observations leads to insufficient spatial resolution of the fault slip on such a shallow plate interface for this reason the location and degree of the slip has not yet been estimated accurately enough to assess future seismic risks thus we estimated the coseismic slip distribution based on terrestrial gps observations and all available seafloor geodetic data that significantly improve the spatial resolution at the shallow portion of the plate interface the results reveal that an extremely large greater than 50 m slip occurred in a small about 40 km in width and 120 km in length area near the japan trench and generated the huge tsunami the estimated slip distribution and a comparison of it with the coupling coefficient distribution deduced from the analysis of the small repeating earthquakes suggest that the 2011 tohoku earthquake released strain energy that had accumulated over the past 1000 years probably since the jogan earthquake in 869 the accurate assessments of seismic risks on very shallow plate interfaces in subduction zones throughout the world can be obtained by improving the quality and quantity of seafloor geodetic observations

interplate coupling in the kanto district central japan and the boso peninsula silent earthquake in may 1996 i studied crustal deformation in the kanto district central japan based on continuous gps data horizontal as well as vertical displacement rate demonstrate significant interaction between the landward kanto block and the philippine sea plate although the subduction effect of the pacific plate is not apparent it is reasonable to consider the entire kanto district is displaced westward due to the interaction with the pacific plate the gps velocity data were inverted to estimate the slip deficit distribution on the sagami trough subduction zone the result delineates a strongly coupled region on the plate interface part of which corresponds to the 1923 kanto earthquake the strongly coupled region is located shallower than 20 km in addition the plate interaction is laterally heterogeneous even in the same depth range implying thermal structure is not the only factor controlling interplate coupling the gps data also detected a silent earthquake event on the interface of the philippine sea slab east of the boso peninsula in the middle of may 1996 the silent rupture propagated over a 50 km 50 km wide area during about a week the maximum slip was approximately 50 mm and the released seismic moment was 4 7 1018nm mw 6 4 there was a small seismicity triggered by this silent event the silent slip was located in the peripheral of the strongly coupled area suggesting that frictional properties and or stress conditions are inhomogeneous on the plate boundary interface

quasi dynamic 3d modeling of the generation and afterslip of a tohoku oki earthquake considering thermal pressurization and frictional properties of the shallow plate boundary the generation of the 2011 tohoku oki earthquake has been modeled by many authors by considering a dynamic weakening mechanism such as thermal pressurization tp because the effects of tp on afterslip have not been investigated this study develops a 3d quasi dynamic model of the earthquake cycle to investigate afterslip of the tohoku oki earthquake considering tp and the geometry of the plate boundary we employ several velocity weakening vw patches for mw 7 class events and two large shallow vw patches the frictional properties are set as velocity strengthening vs outside the vw patches the results show that during megathrust earthquakes fast slip propagates to the surrounding vs regions near the vw patches owing to weakening by tp following mw 9 events large afterslips occur in regions below the northern shallow rupture area in the off fukushima region close to the japan trench which is consistent with observations in the vs region near the vw patches during the early afterslip period frictional behavior exhibits less vs with increasing slip velocity due to pore pressure reduction we also consider the frictional properties of the shallow plate boundary fault off tohoku which exhibits a transition from vw to vs from low to high slip velocities the results show the occurrence of slow slip events sses at intervals of a few decades at the shallow plate boundary during megathrust events the vw property at low slip velocity promotes slip along the shallow sse region more than the case with vs property throughout the entire velocity range

slow slip history for the mexico subduction zone 2005 through 2011 to further our understanding of the seismically hazardous mexico subduction zone we estimate the first time dependent slip distributions and coulomb failure stress changes for the six major slow slip events sses that occurred below mexico between late 2005 and mid 2011 slip dist ributions are the first to be estimated from all continuous gps data in central and southern mexico which better resolves slow slip in space and time than was previously possible in this region below oaxaca slip during previously un modeled sses in 2008 9 and 2010 11 extended farther to the west than previous sses this constitutes the first evidence that slow slip accounts for deep slip within a previously noted gap between the oaxaca and guerrero sse source regions the slip that we estimate for the two sses that originated below guerrero between 2005 and 2011 agrees with slip estimated in previous mostly static offset sse modeling studies however we show that both sses migrated eastward toward the oaxaca sse source region in accord with previous work we find that slow slip below guerrero intrudes up dip into the potentially seismogenic region presumably accounting for some of the missing slip within the well described guerrero seismic gap in contrast slow slip below oaxaca between 2005 and 2011 occurred mostly down dip from the seismogenic regions defined by the rupture zones of large thrust earthquakes in 1968 and 1978 and released all of the slip deficit that accumulated in the down dip region during this period

non volcanic tremor associated with the march 2010 gisborne slow slip event at the hikurangi subduction margin new zealand 1 non volcanic tremor accompanies slow slip events at most circum pacific subduction zones previously the hikurangi subduction margin new zealand and the boso peninsula of japan have been noted as exceptions where slow slip which occurs at shallow depth compared to other subduction zones does not generate seismic tremor the lack of tremor observations raises questions whether tremor and slow slip are manifestations of the same process and whether different temperature and pressure conditions influence the physical mechanism of tremor production analysis of seismic data during the march 2010 gisborne slow slip event new zealand reveals that this slow slip event at the northern hikurangi margin is accompanied by tremor with distinctive characteristics compared to local microearthquakes both the gisborne area of new zealand and the boso peninsula of japan are underlain by thick accumulations of sedimentary rocks that likely inhibit the observation of low amplitude tremor due to high attenuation discovery of tremor in new zealand suggests that tremor may always accompany slow slip and that its apparent absence at the boso peninsula the hikurangi margin prior to this study and any future regions discovered to experience slow slip without concurrent tremor may be the effect of highly attenuating sediments

slow slip and aseismic deformation episodes associated with the subducting pacific plate offshore japan revealed by changes in seismicity 1 aseismic phenomena including slow slip can alter the surrounding seismicity we here investigate how seismicity can be used in order to reveal episodes of aseismic deformation an objective method is proposed that accounts for both earthquake interactions and transient loading applying it to the 1990 2011 pre tohoku seismicity of the japan subduction zone we find several significant instances of aseismic transients small scale and short duration transients are favored updip of the subducting plate large scale transients are mostly observed offshore ibaraki prefecture in a partly decoupled zone that extends downdip the four most intense of such transients have occurred periodically every 5 9years and are likely due to slow slip episodes other aseismic phenomena including possible fluid intrusion in the outer rise are also detected finally the seismicity in january and february 2011 close to the epicenter of the megathrust tohoku earthquake is found to be due to aseismic loading confirming previous studies although this transient is only one among others and is not the most intense nor the most significant for the 21year long period studied here

possible deep fault slip preceding the 2004 parkfield earthquake inferred from detailed observations of tectonic tremor 1 earthquake predictability depends in part on the degree to which sudden slip is preceded by slow aseismic slip recently observations of deep tremor have enabled inferences of deep slow slip even when detection by other means is not possible but these data are limited to certain areas and mostly the last decade the region near parkfield california provides a unique convergence of several years of high quality tremor data bracketing a moderate earthquake the 2004 magnitude 6 0 event here i present detailed observations of tectonic tremor from mid 2001 through 2008 that indicate deep fault slip both before and after the parkfield earthquake that cannot be detected with surface geodetic instruments while there is no obvious short term precursor i find unidirectional tremor migration accompanied by elevated tremor rates in the 3 months prior to the earthquake which suggests accelerated creep on the fault 16 km beneath the eventual earthquake hypocenter

friction velocity dependence of clay rich fault material along a megasplay fault in the nankai subduction zone at intermediate to high velocities 1 the frictional properties of clay rich fault material collected from a megasplay fault within the nankai accretionary complex were examined in frictional experiments performed at a normal stress of 5 mpa under water saturated conditions for slip velocities from 0 0026 to 260 mm s with 250 mm of displacement our results reveal that the fault material can show two stages of velocity weakening behavior weakening at slow velocities v 26 mm s such a process of fault weakening may provide important constraints on models of faulting along a megasplay fault at slip velocities from 0 026 to 2 6 mm s there exist both velocity weakening and velocity strengthening fault materials the frictional coefficient values for slow slip velocities v 0 26 mm s are relatively low 0 28 0 35 for velocity strengthening samples compared with velocity weakening samples 0 38 0 49 microstructural analyses reveal that velocity strengthening samples show homogeneous deformation textures in which the entire gouge layer is deformed whereas velocity weakening materials show evidence of shear localization in which deformation is concentrated along narrow subsidiary shears

geology and petrology of ejecta from the 1999 eruption of shishaldin volcano alaska shishaldin volcano erupted repeatedly during april and may 1999 with major eruptive events on 19 april and 23 april tephra deposits 20 cm thick were distributed across the southern flanks and hyperconcentrated debris flows ran down the northern slope all analyzed clasts were basaltic in composition with abundant 29 vol phenocrysts of plagioclase olivine and magnetite glass inclusion analyses indicate low volatile contents 900 to 58 ppm respectively comparisons of sulfur contents in glass inclusions and groundmass glasses suggest significant degassing occurred even prior to eruption trace element studies suggest that the magma reservoir below shishaldin may not be a closed long lived chamber and u th ra isotopic analyses indicate short crustal residence times on the order of at most a few thousand years for the 1999 products comparison of the deposits from this eruption with other similarly sized eruptions suggests the 19 april explosive event should be classified as a sub plinian basaltic eruption such eruptions are rare the 19 april explosive event was the largest at shishaldin during the last 175 years however the petrology chemistry and deposit thickness and distribution resemble those of at least 11 scoria deposits in the last 9 000 years suggesting that this type of eruption is common for shishaldin

correlated transient fluid pulsing and seismic tremor in the costa rica subduction zone continuous measurements of fluid flow were made over a six month period across the nicoya peninsula costa rica pacific convergent margin utilizing osmotically driven fluid flow meters designed to quantify both inflow and outflow rates on the order of 10 5 to 3 cm d significant transience in flow was observed through the surface of the forearc three periods of correlated flow signals were seen on the subduction forearc among three instruments located in the out of sequence thrust oost zone over along margin strike distances of 30 km amplitudes of ground velocity recorded on collocated ocean bottom seismometers obs increase during the three correlated flow events the seismic signal has frequency characteristics that resemble volcanic and non volcanic tremor we hypothesize that repeated plate boundary slow slip events potentially originating at the up dip limit of the seismogenic zone generate the observed signals within the toe of the forearc we propose a model in which the poro elastic stress strain field around a series of creep dislocations simultaneously forces flow through fracture networks in the forearc and oceanic basement rocks and induces diffuse flow through the shallow sediments the former generates the seismic tremor like noise recorded by the obss and the latter generates the flow transients recorded by the fluid flow meters we suggest that high sensitivity fluid flow meters can be utilized to detect transient tectonic strain events in offshore environments where traditional geodetic techniques lack resolution or are not possible d 2005 elsevier b v all rights reserved

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

active thrusting of the longquan fault in the central sichuan basin china and the seismotectonic behavior in the longmen shan fold and thrust belt present day convergence within the longmen shan fold and thrust belt lsftb was released by the 2008 mw 7 9 wenchuan earthquake which ruptured multiple thrust ramps beneath the range front structures however it is still unclear whether fault slip propagated eastward into the foreland closer to densely populated areas around chengdu in this study we provide constraints on the 3 d subsurface structure fault activity and seismic hazards of the longquan fault located in the central sichuan basin 100 km east of the range front structures of the lsftb we develop a seismotectonic model and assess the activity of the longquan fault by a combination of methods including interpretation of seismic reflection profiles analysis of satellite images field mapping trench logging and radiocarbon dating our survey reveals that at least two surface rupturing events occurred on the longquan fault in the holocene our 3 d structural model and evidence for late holocene faulting events on the longquan fault reveals that upper crustal shortening in the sichuan basin is accommodated by a frontal thrust system that is linked to the recently active range front blind structures by a shallow detachment we suggest that dynamic weakening following fault activity at the longmen shan range front might unlock the up dip portion of this shallow detachment sending slip eastward into the foreland and to the surface along the longquan thrust ramps our results have important implications for seismic hazards assessment of active frontal thrusts linked by upper crustal detachments in active fold and thrust belts around the world

slow earthquakes and great earthquakes along the nankai trough abstract we have reexamined reports indicating that slow deformation occurred before the great japan earthquakes of 1944 tonankai and 1946 nankaido and find that the observations are well founded although no quantitative models have previously been proposed to explain all of the relevant data we show that they are satisfied by a simple model for both earthquakes the model based on known properties of subduction zones has slow slip on the subduction interface in an area deeper than the seismic rupture if this model is correct and a similar physical situation holds for an anticipated tokai earthquake existing instruments will be able to reveal the pre slip in real time while differences among the deformation time series at different sites will provide strong constraints on the slow rupture propagation these differences could result in delaying the recognition of a coherent event

synchronous changes in the seismicity rate and ocean bottom hydrostatic pressures along the nankai trough a possible slow slip event detected by the dense oceanfloor network system for earthquakes and tsunamis donet abstract we detected long term hydrostatic pressure changes at ocean bottom stations of the dense oceanfloor network system for earthquakes and tsunamis donet along the nankai trough off southwestern japan we detected these changes after removing the contributions of ocean mass variations and sensor drift from the records in addition we detected a decrease in the background seismicity rate of a nearby earthquake cluster that was synchronous with the hydrostatic pressure changes we interpreted these observed hydrostatic pressure changes to reflect vertical deformation of the ocean floor of 3 8 cm and we consider the cause of the seafloor crustal deformation to be a slow slip event sse beneath the stations because the pressure changes were observed at stations with distances less than 20 km to each other we inferred that the sse occurred in the shallow part of the sedimentary wedge such as on a splay fault system the synchronous observation of an sse and a seismicity rate change suggests that both were triggered by a change in the regional stress that may be associated with stress accumulation and release processes occurring along the nankai trough these data show that continuous and careful monitoring of crustal activities by donet stations provides an effective way to detect seismic and geodetic signals related to the occurrence of megathrust or other types of large earthquakes

the 2011 tohoku oki earthquake displacement reaching the trench axis we detected and measured coseismic displacement caused by the 11 march 2011 tohoku oki earthquake moment magnitude mw 9 0 by using multibeam bathymetric surveys the difference between bathymetric data acquired before and after the earthquake revealed that the displacement extended out to the axis of the japan trench suggesting that the fault rupture reached the trench axis the sea floor on the outermost landward area moved about 50 meters horizontally east southeast and 10 meters upward the large horizontal displacement lifted the sea floor by up to 16 meters on the landward slope in addition to the vertical displacement

silica diagenesis and its effect on interplate seismicity in cold subduction zones abstract the diagenesis and deformation processes of ribbon cherts embedded in a jurassic accretionary complex central japan were investigated in detail to gain a better understanding of the mechanical behavior of the plate boundary at depth in cold subduction zones the analyzed cherts record two stages of deformation 1 map to outcrop scale ductile folding and 2 subsequent brittle faulting the ductile deformation was facilitated by silica dehydration precipitation and is represented by multiple phases of vein networks the folds are cut by brittle faults indicating lithification and the concurrent mechanical transition from ductile to brittle behavior slip zones along the faults are typically filled with brecciated chert in a chlorite matrix geothermometry analysis of the matrix chlorite suggests that faulting occurred following the completion of opal ct to quartz transition reaction this is also confirmed by the kinetic simulation of silica conversion reactions the results suggest that ductile deformation of thick pelagic deposits with abundant fluids results in an aseismic plate boundary whereas chemical diagenesis of the deposits producing crystalline cherts results in interplate coupling in cold subduction zones such as the japan trench

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

the 2011 magnitude 9 0 tohoku oki earthquake mosaicking the megathrust from seconds to centuries geophysical observations from the 2011 moment magnitude m w 9 0 tohoku oki japan earthquake allow exploration of a rare large event along a subduction megathrust models for this event indicate that the distribution of coseismic fault slip exceeded 50 meters in places sources of high frequency seismic waves delineate the edges of the deepest portions of coseismic slip and do not simply correlate with the locations of peak slip relative to the m w 8 8 2010 maule chile earthquake the tohoku oki earthquake was deficient in high frequency seismic radiation a difference that we attribute to its relatively shallow depth estimates of total fault slip and surface secular strain accumulation on millennial time scales suggest the need to consider the potential for a future large earthquake just south of this event

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

geochemistry of premetamorphic hydrothermal alteration of metasedimentary rocks associated with the gorob massive sulfide prospect damara orogen namibia five massive sulfide lenses and several smaller sulfide occurrences at gorob namibia are hosted by metaturbidites of the kuiseb formation and are associated with amphibolites of the matchless member the strata at gorob are overturned and regionally metamorphosed at staurolite kyanite sillimanite grade in the stratigraphic footwall of the sulfide lenses zones of premetamorphic hydrothermal alteration can be identified which are discordant to the lithostratigraphy hydrothermal alteration of the original sediments is related to submarine exhalative ore forming processes this alteration led to a general enrichment of mg fe mn cu zn ba and p and depletion of ca na k rb sr and ce as demonstrated by comparison with the geochemistry of unaltered kuiseb formation metasediments from gorob and elsewhere on this basis alteration indices can be constructed for major and trace elements these indices show an increase toward the mineralization and a sharp decrease in the stratigraphic hanging wall of the ore zones they are independent of the composition of the original sediment as monitored by the tio 2 zr ratio which remained constant during hydrothermal alteration and metamorphism with the possible exception of ce concentrations of rare earth elements were not modified by the alteration process and may provide information on the provenance of the original sediments

evidence for aseismic deformation rate changes prior to earthquakes abstractfor ten earthquakes in nonmagmatic settings there are credible published accounts of pre earthquake deformation rate changes lasting hundreds of seconds to more than a decade although most m 7 5 earthquakes have occurred without detectable pre earthquake deformation the detection threshold for aseismic deformation remains high in that aseismic slip with moment equivalent to an m5 earthquake would in most although not all cases have been missed interseismic deformation rates vary without being followed by earthquakes and a strain rate change prior to the 1989 mw6 9 loma prieta california earthquake is shown to be similar in size to many other rate changes that have occurred since that time most examples of pre earthquake aseismic deformation lasting hundreds of seconds or more probably originate adjacent to or downdip of the seismic rupture plane rather than within the zone that undergoes seismic failure

laboratory micro seismic signature of shear faulting and fault slip in shale this article reports the results of a triaxial deformation experiment conducted on a transversely isotropic shale specimen this specimen was instrumented with ultrasonic transducers to monitor the evolution of the micro seismic activity induced by shear faulting triaxial failure and subsequent fault slip at two different rates the strain data demonstrate the anisotropy of the mechanical quasi static compliance of the shale the p wave velocity data demonstrate the anisotropy of the elastic dynamic compliance of the shale the spatio temporal evolution of the micro seismic activity suggests the development of two distinct but overlapping shear faults a feature similar to relay ramps observed in large scale structural geology the shear faulting of the shale specimen appears quasi aseismic at least in the 0 5 mhz range of sensitivity of the ultrasonic transducers used in the experiment concomitantly the rate of micro seismic activity is strongly correlated with the imposed slip rate and the evolution of the axial stress the moment tensor inversion of the focal mechanism of the high quality micro seismic events recorded suggests a transition from a non shear dominated to a shear dominated micro seismic activity when the rock evolves from initial failure to larger and faster slip along the fault the frictional behaviour of the shear faults highlights the possible interactions between small asperities and slow slip of a velocity strengthening fault which could be considered as a realistic experimental analogue of natural observations of non volcanic tremors and very low frequency earthquakes triggered by slow slip events

statistical significance of precursory gravity changes before the 2011 mw 9 0 tohoku oki earthquake author s wang l burgmann r abstract 2019 american geophysical union all rights reserved it is of paramount importance to independently assess the spatiotemporal uniqueness of a proposed regional precursor initiated a few months before the 2011 mw 9 0 tohoku oki earthquake the precursor has been inferred from grace derived gravitational gradient changes and has been interpreted as a large scale aseismic movement of the subducting plate along the japan trench we design a hypothesis test which enables the rigorous assessment of the statistical significance of short term gradient anomalies at any time in any place and the quantitative comparison of the resolved anomalies with the proposed precursory signal we find that the proposed precursory changes are not statistically unique either in time or in space therefore the precursor cannot be attributed to the proposed dynamic acceleration of the subduction process instead such transient features more likely represent temporally correlated grace observation errors or signals associated with other processes

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

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

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

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

frontal wedge deformation near the source region of the 2011 tohoku oki earthquake 1 we report an uplift of 5 m with a horizontal displacement of more than 60 m due to the 2011 tohoku oki earthquake the uplift was measured by an ocean bottom pressure gauge installed before the earthquake on a frontal wedge which formed an uplift system near the japan trench horizontal displacements of the frontal wedge were measured using local benchmark displacements obtained by acoustic ranging before and after the earthquake the average displacements at the frontal wedge were 58 m east and 74 m east southeast these results strongly suggest a huge coseismic slip beneath the frontal wedge on the plate boundary the estimated magnitude of the slip along the main fault was 80 m near the trench our results suggest that the horizontal and vertical deformations of the frontal wedge due to the slip generated the tremendous tsunami that struck the coastal area of northeastern japan

a large slow slip event on the central hikurangi subduction interface beneath the manawatu region north island new zealand 1 we present continuous gps observations of a surface deformation episode in the manawatu region of the north island new zealand lasting 18 months from january 2004 to june 2005 we invert vertical and horizontal displacements of gps sites during the event for slow slip on the hikurangi subduction thrust we find that up to 350 mm of slip occurred on the thrust in the transition zone between strong interseismic coupling and aseismic creep if the entire slip in the manawatu slow slip event had occurred instantaneously it would have resulted in an mw 7 0 earthquake given the large amount of slip we expect that the recurrence interval for similar slow slip events may be ten years or more

nucleation of frictional instability caused by fluid pressurization in subducted blueschist pore pressure is an important factor in controlling the slip instability of faults and thus the generation of earthquakes particularly slow earthquakes are widespread in subduction zones and usually linked to the occurrence of high pore pressure yet the influence of fluid pressure and effective stress on the mechanics of earthquakes is poorly understood therefore we performed shear experiments on blueschist fault rocks which likely exist at depth in cold and old subduction zones to investigate the influence of effective stress on frictional behavior our results show potentially unstable behavior at temperatures characterizing the seismogenic zone as well as a transition from stable to unstable behavior with decreasing effective normal stress which is mechanically equivalent to increasing fluid pressure this transition is a prerequisite for generating slow earthquakes our results imply that high pore pressures are a key factor for nucleating slip leading to both megathrust and slow earthquakes

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

variability of near term probability for the next great earthquake on the cascadia subduction zone the threat of a great m 9 earthquake along the cascadia subduction zone is evidenced by both paleoseismology data and current strain accumulation along the fault on the basis of recent information on the characteristics of this subduction system we estimate the conditional probabilities of a great earthquake occurring within the next 50 years and their variabilities the most important vari ation is associated with the existence of episodic slow slip on the deep portion of the subduction interface we show that these events modulate the conditional probability dramatically over their 14 month cycle during the 2 week slow slip events the weekly probability of a great earthquake is about 30 to 100 times as high as it is during any week of the rest of the year near term probabilities also vary significantly with the assumed distribution of earthquake recurrence intervals under a reference scenario of unimodal distribution of recurrence intervals about 500 600 years the 50 year conditional probability is low 0 12 at a 95 confidence interval how ever under a tantalizing bimodal distribution hypothesis this probability could be either four times as high 6 45 or four times as low less than 1 depending on whether the current interval is short 350 years or long 850 years

trench normal variation in observed seafloor displacements associated with the 2011 tohoku oki earthquake 1 seafloor geodetic measurements using the gps acoustic technique just above the rupture area of the 2011 tohoku oki earthquake revealed strong trench normal variation in the horizontal crustal displacement associated with the earthquake one set of observations at a site only 50 km away from the trench yielded the most trench ward data ever reported with an accuracy better than 1 m it showed a coseismic displacement of up to 31 m whereas another set of observations 100 km away from the trench showed a 15 m displacement these horizontal data as well as vertical data from pressure gauges and tsunami observations strongly indicate that the seismic slip reached the trench they are also likely to contribute quantitatively to further investigations that reveal the coseismic behavior of the frontal wedge of the overriding plate in the source region along the japan trench

continuous gps array and present day crustal deformation of japan a gps array with about 1 000 permanent stations is under operation in japan the gps array revealed coseismic deformations associated with large earthquakes and ongoing secular deformation in the japanese islands based on daily coordinate data of the gps stations strain rate distribution is estimated most regions with a large strain rate are related to plate boundaries and active volcanoes in addition the niigata kobe tectonic zone nktz is recognized as a region of large strain rate along the japan sea coast and in the northern chubu and kinki districts this newly found tectonic zone may be related to a hypothetical boundary between the eurasian or amurian and the okhotsk or north america plates precise observation of crustal deformation provides important boundary conditions on numerical modeling of earthquakes and other crustal activities appropriate computation methods of continuous deformation field are directly applicable to data assimilation for such numerical simulations

recurring slow slip events and earthquake nucleation in the source region of the m 7 ibaraki oki earthquakes revealed by earthquake swarm and foreshock activity

displacement above the hypocenter of the 2011 tohoku oki earthquake the moment magnitude m w 9 0 2011 tohoku oki mega thrust earthquake occurred off the coast of northeastern japan combining global positioning system gps and acoustic data we detected very large sea floor movements associated with this event directly above the focal region an area with more than 20 meters of horizontal displacement that is four times larger than those detected on land stretches several tens of kilometers long along the trench the largest amount reaches about 24 meters toward east southeast just above the hypocenter furthermore nearly 3 meters of vertical uplift occurred contrary to observed terrestrial subsidence

effective resolution and drift of paroscientific pressure sensors derived from long term seafloor measurements 1 starting with the installation of the noaa tsunami early warning system dart in 1983 the paroscientific digiquarz broadband depth sensor has been deployed for long term ocean bottom pressure measurements in numerous marine investigations the sensor turned out to be very reliable with a good signal repeatability within a broad measuring range and high resolution however up to now its long term drift noise level and effective resolution under in situ conditions at the seafloor are only known from a few published studies and for a few sensors in this study we analyze 118 long term seafloor pressure time series longer than 2 months and up to a maximum time period of 9 years to investigate effective resolution and long term drift under in situ conditions the data are from dart ifm geomar lolem and cork stations the noise level of the data and therefore the mean sensor resolution are lower than an upper threshold of 20 7 pa corresponding to 2 07 mm equivalent water level for stations installed directly on the seafloor the noise level of cork sensors is much larger with a median value of 127 pa long term sensor drift is assumed to be composed of an initial exponential part and a subsequent linear drift in situ mean drift is 0 88 0 73 kpa a determined from all available data with a slight increase of drift with deployment depth for the first time we are able to quantify effective pressure resolution and drift of the widely used paroscientific pressure gauges under in situ conditions our results provide important constrains for the interpretation of seafloor pressure records however in situ self calibration procedures for the paroscientific sensors are still needed in order to benefit from high effective resolution and long term stability and also to increase accuracy especially for the monitoring of geodynamic processes at the seafloor

hydrologic detection and finite element modeling of a slow slip event in the costa rica prism toe 1 we investigate transient fluid flux through the seafloor recorded near the costa rica trench during the 2000 costa rica seismogenic zone experiment using a 2 d fully coupled poroelastic finite element model we demonstrate that the observed hydrologic anomalies are consistent with a model of propagating slow slip at the subduction interface between the frontal prism and downgoing plate there are two sources of volumetric strain that drive fluid flux at the seafloor in response to fault slip at depth 1 compression and dilation in the vicinity of the tips of a slipping patch and 2 extension and compression due to flexure of the seafloor the superposition of these two effects results in distinctive spatial and temporal patterns of fluid flow through the seafloor in a forward modeling approach time series from shear ruptures with a range of fault length to depth ratios in a heterogeneous crust are generated and compared with flow rate observations assuming a constant propagation rate and an elliptical profile for the distribution of slip along the decollement the set of model predictions enables us to infer the probable rupture location extent propagation velocity and duration from a single flow rate time series the best fit model suggests that the slow slip event initiated within the toe at a depth of less than 4 km and propagated bilaterally at an average rate of 0 5 km d 1 this interpretation implies that stress in the shallow subduction zone is relieved episodically furthermore the costa rica data suggest that episodic slow slip events may initiate in the prism toe without being triggered by a seismic event further downdip

slow and fast ruptures on a laboratory fault controlled by loading characteristics recent geodetic observations indicate that a single fault may slip slowly and silently or fast and seismically in different circumstances we report laboratory experiments that demonstrate how the mode of faulting can alternate between fast stick slip events 70 to 500 mm s sliding rates and slow silent events 0 001 to 30 mm s as a result of loading conditions rather than friction properties or stiffness of the loading machine the 760 mm long granite sample is close to the critical nucleation length scale for unstable slip so small variations in nucleation properties result in measurable differences in slip events slow events occur when instability cannot fully nucleate before reaching the sample ends dynamic events occur after long healing times or abrupt increases in loading rate which suggests that these factors shrink the spatial and temporal extents of the nucleation zone arrays of slip strain and ground motion sensors installed on the sample allow us to quantify seismic coupling and study details of premonitory slip and afterslip we find that seismic coupling decreases when slip rates fall below about 70 mm s the slow slip events we observe are primarily aseismic less than 1 of the seismic coupling of faster events and produce swarms of very small m 6 to m 8 events these mechanical and seismic interactions suggest that faults with transitional behavior where creep small earthquakes and tremor are often observed could become seismically coupled if loaded rapidly either by a slow slip front or dynamic rupture of an earthquake that nucleated elsewhere

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

far field triggering of foreshocks near the nucleation zone of the 5 september 2012 m w 7 6 nicoya peninsula costa rica earthquake abstract on 5 september 2012 a moment magnitude mw 7 6 earthquake occurred directly beneath the nicoya peninsula an area with dense seismic and geodetic network coverage the mainshock ruptured a portion of a previously identified locked patch that was recognized due to a decade long effort to delineate the megathrust seismic and aseismic processes in this area here we conduct a comprehensive study of the seismicity prior to this event utilizing a matched filter analysis that allows us to decrease the magnitude of catalog completeness by 1 unit we observe a statistically significant increase in seismicity rate below the nicoya peninsula following the 27 august 2012 mw 7 3 el salvador earthquake about 450 km to the northwest and 9 days prior to the nicoya earthquake additionally we identify a cluster of small magnitude

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

low frequency tremors associated with reverse faults in a shallow accretionary prism abstract the shallow part of a seismogenic subduction zone is thought to play an important role in tsunami genesis during large interplate thrust earthquakes near the updip portion of the seismogenic zone along the nankai trough splay faults which are major active reverse faults in the accretionary prism likely rupture during large interplate earthquakes such as the 1944 m w 8 2 tonankai earthquake off kii peninsula we observed low frequency tremors associated with reverse faults in a shallow accretionary prism off kii peninsula at close range by using ocean bottom seismographs the tremors were characterized by a dominant frequency range of 2 8 hz and a lack of energy in the frequency range above 10 hz their duration ranged from tens of seconds to a few minutes their source locations lay in three clusters on the landward slope of the nankai trough activity in each cluster continued for from one day to two weeks many of the low frequency tremors were located near the shallowest part of a major splay fault the episodic activity of low frequency tremors and of previously reported very low frequency earthquakes which indicate reverse faulting in the shallow accretionary prism suggests that the reverse faults in the accretionary prism are conditionally stable faults that can become unstable under sufficiently strong dynamic loading such as that caused by a large earthquake such reverse faults as typified by a splay fault can rupture during large interplate earthquakes and generate large tsunamis

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