litho1 0 an updated crust and lithospheric model of the earth we present the litho1 0 model which is a 1 tessellated model of the crust and uppermost mantle of the earth extending into the upper mantle to include the lithospheric lid and underlying asthenosphere the model is parameterized laterally by tessellated nodes and vertically as a series of geophysically identified layers such as water ice sediments crystalline crust lithospheric lid and asthenosphere litho1 0 is created by constructing an appropriate starting model and perturbing it to fit high resolution surface wave dispersion maps love and rayleigh group and phase over a wide frequency band 5 40 mhz we examine and discuss the model with respect to key lithospheric parameters such as average crustal velocity crustal thickness upper mantle velocity and lithospheric thickness we then compare the constructed model to those from a number of select studies at regional and global scales and find general consistency it appears that litho1 0 represents a reasonable starting model of the earth s shallow structure crust and uppermost mantle for the purposes in which these models are used such as traveltime tomography or in efforts to create a 3 d reference earth model the model matches surface wave dispersion over a frequency band wider than the band used in the inversion there are several avenues for improving the model in the future by including attenuation and anisotropy as well as making use of surface waves at higher frequency

plate boundary observatory and related networks gps data analysis methods and geodetic products the geodesy advancing geosciences and earthscope gage facility global positioning system gps data analysis centers produce position times series velocities and other parameters for approximately two thousand continuously operating gps receivers spanning a quadrant of earth s surface encompassing the high arctic north america and caribbean the purpose of this review is to document the methodology for generating station positions and their evolution over time and to describe the requisite tradeoffs involved with combination of results gage gps analysis involves formal merging within a kalman filter of two independent loosely constrained solutions one is based on precise point positioning produced with the gps inferred positioning system orbit analysis simulation gipsy oasis software at central washington university cwu and the other is a network solution based on phase and range double differencing produced with the gps at mit gamit software at new mexico institute of mining and technology nmt the primary products generated are the position time series that show motions relative to a north america reference frame and secular motions of the stations represented in the velocity field the position time series themselves contain a multitude of signals in addition to the secular motions co seismic and post seismic signals seasonal signals from hydrology and transient events some understood and other not yet fully explained are all evident in the time series and ready for further analysis and interpretation we explore the impact of analysis assumptions on the reference frame realization and on the final solutions and we compare within the gage solutions and with others

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

the seismic cycle in the area of the 2011 mw9 0 tohoku oki earthquake we model seismic and aseismic slip on the japan megathrust in the area of the m w9 0 2011 tohoku oki earthquake based on daily time series from 400 gps stations of the geonet network and campaign measurements of six sea floor displacements the coseismic and postseismic slip distributions are inverted simultaneously using principal component analysis based inversion method pcaim exploring a wide range of boundary conditions and regularization constraints we found the coseismic slip distribution to be quite compact with a peak slip between 30 and 50 m near the trench our model shows deep afterslip fringing the downdip edge of the coseismic rupture but also a dominant zone of shallow afterslip afterslip over the first 279 days following the main shock represents about 40 of the coseismic moment we compare the coseismic and postseismic models with an interseismic coupling model derived from inland and sea bottom measurements determined in a self consistent manner assuming that seismic and aseismic slip had to match the long term slip rate along the megathrust the recurrence time of m w9 0 earthquakes is estimated to 100 300 years while historical and paleotsunami records suggest a return period more of the order of 1000 years the discrepancy is smaller if the shallower portion of the megathrust is assumed to produce both aseismic slip as the afterslip model suggests and seismic slip during occasional large tsunamigenic earthquakes

source parameters and time dependent slip distributions of slow slip events on the cascadia subduction zone from 1998 to 2008 1 we invert for the time dependent slip history of slow slip events on the cascadia subduction zone using gps data from 1998 to 2008 the 16 slip transients have sufficient station coverage to solve for the slip distribution on the plate interface gps time series are inverted for fault slip using the extended network inversion filter limited station coverage south of portland 45 5 n latitude restricts our analysis to events on the northern half of the subduction zone slip is resolved at the base of the seismogenic zone and the slip distributions suggest a potential segment boundary near seattle 47 6 n that correlates roughly with geologic and tectonic boundaries events that initiate to the north and south tend to overlap at about this latitude we compile statistics on source parameters such as propagation rate recurrence interval and stress drop which can be used to constrain proposed models of the source mechanics over a 10 year period total strain release from slow slip events is nonuniform along strike with the greatest cumulative slip 27 cm centered beneath port angeles 48 1 n this slip patch also exhibits the most regular recurrence of mw 6 events relative to other locations along strike the spatial extent of the slip patch beneath port angeles correlates with the along strike bend of the cascadia subduction zone in northwestern washington suggesting that plate geometry plays an important role in controlling the along strike characteristics of slow slip

elevated pore pressure and anomalously low stress in regions of low frequency earthquakes along the nankai trough subduction megathrust 1 recent seismic reflection and ocean bottom seismometer obs studies reveal broad regions of low seismic velocity along the nankai subduction plate boundary megathrust offshore sw japan these low velocity zones lvz s extend 55 km landward from the trench corresponding to depths of 10 km below sea floor here we estimate the in situ pore pressure and stress state within these lvz s by combining p wave velocities obtained from the geophysical surveys with new well constrained empirical relations between p wave velocity porosity and effective mean stress defined by laboratory deformation tests on drill core samples of the incoming oceanic sediment we document excess pore pressures of 17 87 mpa that extend 55 km into the subduction zone indicating that trapped pore fluids support 45 91 of the overburden stress along the base of the upper plate and surrounding major fault zones the resulting effective stresses in the lvz are limited to 1 3 of the values expected for non overpressured conditions these low effective stresses should lead to a mechanically weak and predominantly aseismic plate boundary the region of lowest effective stress coincides with precisely located very low frequency earthquakes providing the first quantitative evidence linking these anomalous slip events to low stress and high pore pressure

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

body tides on a 3 d elastic earth toward a tidal tomography abstract the deformational and gravitational response of the earth to the tide generating potential has generally involved 1 d i e depth varying earth models progressive improvement in observational constraints on body tides generated from both ground and space based surveys suggests that an examination of the potential impact of lateral variations in earth structure is warranted we present a suite of predictions of the body tide response within the semi diurnal diurnal and long period tidal bands computed using a finite volume numerical code the calculations adopt 3 d density and elastic structure taken from seismic inferences and in a subset of the calculations dynamic topography on the surface and internal interfaces we find that perturbations in the radial displacement and surface gravity within the semi diurnal band reach 1 mm and 0 15 gal respectively the perturbations in the diurnal band are comparable to these values and within the long period band they are a factor of 3 5 smaller we also demonstrate that lateral variations in the elastic moduli which have been ignored in recent work contribute greater than 50 of the total perturbation the level of perturbation associated with 3 d structure exceeds the current observational uncertainty obtainable using space geodetic methods and this suggests the possibility of performing tidal tomographic inversions of such data

accuracy assessment of global barotropic ocean tide models the accuracy of state of the art global barotropic tide models is assessed using bottom pressure data coastal tide gauges satellite altimetry various geodetic data on antarctic ice shelves and independent tracked satellite orbit perturbations tide models under review include empirical purely hydrodynamic forward and assimilative dynamical i e constrained by observations ten dominant tidal constituents in the diurnal semidiurnal and quarter diurnal bands are considered since the last major model comparison project in 1997 models have improved markedly especially in shallow water regions and also in the deep ocean the root sum square differences between tide observations and the best models for eight major constituents are approximately 0 9 5 0 and 6 5 cm for pelagic shelf and coastal conditions respectively large intermodel discrepancies occur in high latitudes but testing in those regions is impeded by the paucity of high quality in situ tide records long wavelength components of models tested by analyzing satellite laser ranging measurements suggest that several models are comparably accurate for use in precise orbit determination but analyses of grace intersatellite ranging data show that all models are still imperfect on basin and subbasin scales especially near antarctica for the m2 constituent errors in purely hydrodynamic models are now almost comparable to the 1980 era schwiderski empirical solution indicating marked advancement in dynamical modeling assessing model accuracy using tidal currents remains problematic owing to uncertainties in in situ current meter estimates and the inability to isolate the barotropic mode velocity tests against both acoustic tomography and current meters do confirm that assimilative models perform better than purely hydrodynamic models

time dependent modeling of slow slip events and associated seismicity and tremor at the hikurangi subduction zone new zealand we present a time dependent slip model of 12 slow slip events sses occurring in the hikurangi margin of new zealand during 2010 and 2011 this model is obtained by inverting daily gps solutions from geonet s continuous gps network on the north island and northern south island we compare the properties of these sses to observations in japan cascadia and mexico and find that hikurangi sses have comparatively large amounts of slip up to 27 cm high slip rates up to 1 4 cm d and a large range of depths 10 40 km durations 7 270 days and sizes mw 5 9 6 9 we further investigate the relationship between the cape turnagain sse and an associated seismic swarm and find that observations are consistent with stress triggering outside the slowly slipping region however other explanations cannot be ruled out we also compare slip during the long term manawatu sse with the tremor epicenters found by ide 2012 and note that tremor locations are offset in the downdip direction relative to the slipping region similar to observations in the bungo channel of japan and guerrero mexico

engineering geological characteristics and processes of permafrost along the qinghai xizang tibet highway abstract engineering geological problems of thaw settlement and frost heave occur frequently along the qinghai xizang tibet highway qxh line and produce an adverse impact on roadbed stability eight monitoring sites were established along the qxh to investigate the engineering geological characteristics and environmental process of permafrost including the upper and lower boundary of the active layer under the natural surface the seasonal freeze thaw depth under the asphalt pavement the permafrost table temperature and roadbed stability the investigation results show that the active layer thickness and permafrost table temperature under an asphalt pavement are higher than under a natural surface due to the absorption heat and reduced evaporation capability of the asphalt pavement the implication for highway design and construction in permafrost areas are discussed

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

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

non volcanic tremor resulting from the combined effect of earth tides and slow slip events swarms of non volcanic tremor in southeastern japan are associated with slow slip events and tend to occur with a periodicity of 12 or 24 h this periodicity can be reproduced by a combination of stresses due to earth tides and transient stress changes caused by slow slip events non volcanic tremors may therefore be useful for understanding stress relaxation at the subduction zone interface slow slip events1 are accompanied by swarms of non volcanic tremor2 3 along the subduction zone of the philippine sea plate in southwest japan the swarms often occur with a periodicity of about 12 or 24 h refs 4 5 these episodic events are considered to be a manifestation of stress relaxation at the subducting plate interface1 6 7 here we analyse seismic data to record the locations and durations of non volcanic tremor swarms that occurred in may 2005 and february 2006 we evaluate the magnitude of stress changes produced by slow slip events as well as the effective normal stress on the plate interface where slow slip events occur we find that the observed periodicity in tremor occurrence originates from a combined effect of the periodic stress due to earth tides and the transient stress due to slow slip events our calculations show that non volcanic tremor is sensitive to stress change this phenomenon can therefore be effective in monitoring the process of stress relaxation at subducting plate interfaces

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

spatial and temporal evolution of stress and slip rate during the 2000 tokai slow earthquake 1 we investigate an ongoing silent thrust event in the tokai seismic gap along the suruga nankai trough central japan prior to the event continuous gps data from april 1996 to the end of 1999 show that this region displaced 2 cm yr to the northwest relative to the landward plate the gps time series show an abrupt change in rate in mid june 2000 that continues as of mid 2005 we model this transient deformation which we refer to as the tokai slow thrust slip event as caused by slip on the interface between the philippine sea and amurian plates the spatial and temporal distribution of slip rate is estimated with kalman filter based inversion methods our inversions reveal two slow subevents the first initiated in late june 2000 slightly before the miyake jima eruption the locus of slip then propagated southeast in the second half of 2000 with maximum slip rates of about 15 cm yr through 2001 a second locus of slip initiated to the northeast in early 2001 the depth of the slip zone is about 25 km which may correspond to the transition zone from a seismogenic to a freely sliding zone the cumulative moment magnitude of the slow slip event up to november 2002 is mw 6 8 we calculate shear stress changes on the plate interface from the slip histories stress change as a function of slip rate shows trajectories similar to that inferred for high speed ruptures however the maximum velocity is 8 orders of magnitude less than in normal earthquakes

imaging of aseismic fault slip transients recorded by dense geodetic networks summary the large scale continuous gps networks that have emerged in the last decade have documented a wide range of aseismic deformation transients that resulted from physical processes such as aseismic fault slip and magma intrusion in particular a new class of m 7 slow earthquakes with durations ranging from days to months have been observed with gps arrays located above the downdip portion of subduction zone thrust interfaces interpretation of the displacement time series resulting from these events is not straightforward owing to the contaminating effects of multiple contributing signals such as fault slip local benchmark motion seasonal effects and reference frame errors we have developed a time dependent inversion algorithm based on the extended kalman filter which can separate the various signals and allow the space time evolution of these slow slip transients to be studied in detail we applied the inversion algorithm to the 1999 cascadia slow earthquake this event had two primary episodes of moment release separated by a two week period in which relatively little moment release occurred the cascadia event and other slow earthquakes share numerous similarities with both ordinary earthquakes and afterslip transients suggesting that they may represent fault slip under a conditionally stable regime

prevalence of viscoelastic relaxation after the 2011 tohoku oki earthquake seafloor global positioning system observations immediately after the great 2011 tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than just afterslip on the fault as is commonly assumed this paper presents revised estimates of the afterslip following the 2011 tohoku oki earthquake based on seafloor gps observations made immediately after the earthquake tianhaozhe sun et al obtain unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation rather than elastic afterslip on the fault as is commonly assumed they conclude that models which erroneously assume an elastic earth substantially overestimate afterslip downdip of the rupture zone and underestimate afterslip updip after a large subduction earthquake crustal deformation continues to occur with a complex pattern of evolution1 this postseismic deformation is due primarily to viscoelastic relaxation of stresses induced by the earthquake rupture and continuing slip afterslip or relocking of different parts of the fault2 3 4 5 6 when postseismic geodetic observations are used to study earth s rheology and fault behaviour it is commonly assumed that short term a few years deformation near the rupture zone is caused mainly by afterslip and that viscoelasticity is important only for longer term deformation6 7 however it is difficult to test the validity of this assumption against conventional geodetic data here we show that new seafloor gps global positioning system observations immediately after the great tohoku oki earthquake provide unambiguous evidence for the dominant role of viscoelastic relaxation in short term postseismic deformation these data reveal fast landward motion of the trench area opposing the seaward motion of gps sites on land using numerical models of transient viscoelastic mantle rheology we demonstrate that the landward motion is a consequence of relaxation of stresses induced by the asymmetric rupture of the thrust earthquake a process previously unknown because of the lack of near field observations our findings indicate that previous models assuming an elastic earth will have substantially overestimated afterslip downdip of the rupture zone and underestimated afterslip updip of the rupture zone our knowledge of fault friction based on these estimates therefore needs to be revised

a comparison of predicted and observed ocean tidal loading in alaska we investigate the elastic and anelastic response of the crust and upper mantle across alaska to mass loading by ocean tides gps inferred surface displacements recorded by the plate boundary observatory network are compared with predictions of deformation associated with the redistribution of ocean water due to the tides we process more than 5 yr of gps data from 131 stations using a kinematic precise point positioning algorithm and estimate tidal contributions using harmonic analysis we also forward calculate load induced surface displacements by convolving ocean tide models with load green s functions derived from spherically symmetric earth models we make the comparisons for dominant tidal harmonics in three frequency bands semidiurnal m diurnal o and fortnightly m f vector differences between predicted and observed ocean tidal loading otl displacements are predominantly sub mm in magnitude in all three frequency bands and spatial components across the network with larger residuals of up to several mm in some coastal areas accounting for the effects of anelastic dispersion in the upper mantle using estimates of q from standard earth models reduces the residuals for the m harmonic by an average of 0 1 0 2 mm across the network and by more than 1 mm at some individual stations for the relatively small m f tide the effects of anelastic dispersion 0 03 mm are undetectable within current measurement error incorporating a local ocean tide model for the northeastern pacific ocean reduces the m vertical residuals by an average of 0 2 mm with improvements of up to 5 mm at some coastal stations estimated rms observational uncertainties in the vertical component for the m and o tides are approximately 0 08 mm at the two sigma level 0 03 mm in the horizontal components and 0 21 mm for the m f harmonic 0 07 mm in the horizontal components for the m harmonic discrepancies between predicted and observed otl displacements exceed observational uncertainties by about one order of magnitude none of the ocean tide and earth model combinations is found to reduce the m residuals below the observational uncertainty and no single forward model provides a best fit to the observed displacements across all tidal harmonics and spatial components for the o harmonic discrepancies between predicted and observed displacements are generally several fold larger than the observational uncertainties for the m f harmonic the discrepancies are roughly within a factor of two of the observational uncertainties we find that discrepancies between predicted and observed otl displacements can be significantly reduced by removing a network uniform tidal harmonic displacement and that the remaining discrepancies exhibit some regional scale spatial coherency particularly for the m harmonic we suggest that the remaining discrepancies for the m o and m f tides cannot be fully explained by measurement error and instead convey information about deficiencies in ocean tide models and deviations from spherically symmetric earth structure

slow earthquakes and nonvolcanic tremor nonvolcanic tremor is observed in close association with geodetically observed slow slip events in subduction zones accumulating evidence points to these events as members of a family of slow earthquakes that occur as shear slip on the downdip extensions of fault zones in a regime that is transitional between a frictionally locked region above and a freely slipping region below by virtue of their locations and their properties slow earthquakes are certain to provide new insights into the behavior of earthquakes and faulting and into the hazard they embody

simulations of tremor related creep reveal a weak crustal root of the san andreas fault 1 deep aseismic roots of faults play a critical role in transferring tectonic loads to shallower brittle crustal faults that rupture in large earthquakes yet until the recent discovery of deep tremor and creep direct inference of the physical properties of lower crustal fault roots has remained elusive observations of tremor near parkfield ca provide the first evidence for present day localized slip on the deep extension of the san andreas fault and triggered transient creep events we develop numerical simulations of fault slip to show that the spatiotemporal evolution of triggered tremor near parkfield is consistent with triggered fault creep governed by laboratory derived friction laws between depths of 20 35 km on the fault simulated creep and observed tremor northwest of parkfield nearly ceased for 20 30 days in response to small coseismic stress changes of order 104 pa from the 2003 m6 5 san simeon earthquake simulated afterslip and observed tremor following the 2004 m6 0 parkfield earthquake show a coseismically induced pulse of rapid creep and tremor lasting for 1 day followed by a longer 30 day period of sustained accelerated rates due to propagation of shallow afterslip into the lower crust these creep responses require very low effective normal stress of 1 mpa on the deep san andreas fault and near neutral stability frictional properties expected for gabbroic lower crustal rock

triggering of tremors and slow slip event in guerrero mexico by the 2010 mw 8 8 maule chile earthquake 1 we investigate the triggering of seismic tremor and slow slip event in guerrero mexico by the february 27 2010 maule earthquake mw 8 8 triggered tremors start with the arrival of s wave generated by the maule earthquake and keep occurring during the passing of scs ss love and rayleigh waves the rayleigh wave dispersion curve footprints the high frequency energy envelope of the triggered tremor indicating a strong modulation of the source of tremors by the passing surface wave this correlation and modulation by the passing waves is progressively lost with time over a few hours the tremor activity continues during the weeks months after the earthquake gps time series suggest that the second sub event of the 2009 2010 sse in guerrero is actually triggered by the maule earthquake the southward displacement of the gps stations starts coincidently with the earthquake and tremors the long duration of tremors indicate a continuing deformation process at depth which we propose to be the second sub event of the 2009 2010 sse we show a quasi systematic correlation between surface displacement rate measured by gps and tremor activity suggesting that the nvt are controlled by the variations in the slip history of the sse this study shows that two types of tremors emerge 1 those directly triggered by the passing waves and 2 those triggered by the stress variations associated with slow slip this indicates the prominent role of aseismic creep in the mexican subduction zone response to a large teleseismic earthquake possibly leading to large scale stress redistribution

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

stresses in the subducting slab beneath southwest japan and relation with plate geometry tectonic forces slab dehydration and damaging earthquakes 1 we infer stresses in the subducting slab beneath southwest japan from focal mechanisms and discuss their geodynamical implications the majority of the 824 fault plane solutions used in this study were obtained by the japan meteorological agency for earthquakes that occurred during 1970 2002 and were previously unpublished the focal mechanisms are believed to reflect stresses in both the untransformed slab crust and the slab mantle the stresses are controlled by tectonic forces and the earthquakes are facilitated by local dehydration the slab experiences a regional e w stretch that is downdip and margin parallel tension at the kyushu and nankai margins respectively we propose that the margin parallel component of mantle resistance to the obliquely subducting young slab at nankai provides an easterly stretch acting against the westerly slab pull of the older and colder part of the slab at northern kyushu despite the complex slab geometry along the nankai margin the direction of tension is largely parallel with the local strike of the slab indicating that the slab is a stress guide the complex slab geometry is not related to the present stress regime but likely reflects severe deformation in the past when an extremely young and incompetent plate was forced to subduct against its own buoyancy the maximum margin parallel stretch and a sharp bending of the slab both occur in the area of the 2001 m 6 7 geiyo earthquake using a simple strength envelope model we demonstrate that normal faulting failure of the slab mantle can occur under such conditions

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

precise comparisons of bottom pressure and altimetric ocean tides 1 a new set of pelagic tide determinations is constructed from seafloor pressure measurements obtained at 151 sites in the deep ocean to maximize precision of estimated tides only stations with long time series are used median time series length is 567 days geographical coverage is considerably improved by use of the international tsunami network but coverage in the indian ocean and south pacific is still weak as a tool for assessing global ocean tide models the data set is considerably more reliable than older data sets the root mean square difference with a recent altimetric tide model is approximately 5 mm for the m2 constituent precision is sufficiently high to allow secondary effects in altimetric and bottom pressure tide differences to be studied the atmospheric tide in bottom pressure is clearly detected at the s1 s2 and t2 frequencies the altimetric tide model is improved if satellite altimetry is corrected for crustal loading by the atmospheric tide models of the solid body tide can also be constrained the free core nutation effect in the k1 love number is easily detected but the overall estimates are not as accurate as a recent determination with very long baseline interferometry

slip rate and tremor genesis in cascadia at many plate boundaries conditions in the transition zone between seismogenic and stable slip produce slow earthquakes in the cascadia subduction zone these events are consistently observed as slow aseismic slip on the plate interface accompanied by persistent tectonic tremor however not all slow slip at other plate boundaries coincides spatially and temporally with tremor leaving the physics of tremor genesis poorly understood here we analyze seismic geodetic and strainmeter data in cascadia to observe for the first time a large tremor generating slow earthquake change from tremor genic to silent and back again the tremor falls silent at reduced slip speeds when the migrating slip front pauses as it loads the stronger adjacent fault segment to failure the finding suggests that rheology and slip speed regulated stressing rate control tremor genesis and the same section of fault can slip both with and without detectable tremor limiting tremor s use as a proxy for slip

dynamic deformation of the accretionary prism excites very low frequency earthquakes 1 we have detected anomalous very low frequency earthquakes within the accretionary prism along the nankai trough southwestern japan centroid moment tensor inversion analysis reveals that the earthquake hypocenters are distributed at 10 km depth above the upper surface of the subducting philippine sea plate and within 50 70 km landward of the trough axis the focal mechanisms indicate reverse faulting their hypocenters are distributed beneath a deformation zone of an accretionary prism in sea floor topography these observations suggest that the occurrence of very low frequency earthquakes is related to numerous reverse fault systems within the accretionary prism and that the earthquakes reflect the dynamics of deformation within this accretionary prism

shortening of recurrence interval of boso slow slip events in japan a slow slip event occurred off the coast of the boso peninsula japan from approximately 28 december 2013 to 10 january 2014 the estimated aseismic slip expanded slightly southward and westward over time with a moment magnitude of 6 5 which was the smallest value since 1996 the recurrence interval has decreased from approximately 6 4 to 2 2 years from 1996 to 2014 one explanation of this shortening is the change in coulomb failure stress due to the 2011 mw9 0 tohoku earthquake and its afterslip another interpretation is related to a scenario observed in several numerical simulation studies in which the recurrence interval of slow slip becomes shorter as the time nears a large earthquake this case will constrain the physical processes of a slip cycle the boso slow slip events together with the tohoku earthquake and its afterslip changed the stress state for the anticipated interplate earthquake near the sagami trough

high vp vs zone accompanying non volcanic tremors and slow slip events beneath southwestern japan abstract in southwestern japan the philippine sea plate subducts beneath the eurasian plate non volcanic tremors and slow slow slip events are observed beneath southwestern japan seismic tomography based on the data obtained from the dense seismic network revealed the velocity structure in and around the subducting philippine sea plate the oceanic crust of the philippine sea plate subducting from the suruga and nankai troughs can be imaged clearly beneath the tokai region and the kii peninsula non volcanic tremors and short term slow slip events may occur in the high vp vs zones owing to the fluid dehydrated from the subducting plate where the oceanic crust of the philippine sea plate encounters the serpentinized wedge mantle of the eurasian plate these tremors and short term slow slip events occur in the high vp vs zone at depths of 30 40 km beneath the tokai region the landward edge of the high vp vs zone beneath the kii peninsula and eastern shikoku region and the seaward edge of the high vp vs zone beneath the western shikoku region long term slow slip events were observed beneath the tokai region and the bungo channel and both these events are located on the seaward side of a high vp vs zone these long term slow slip events are considered to be caused at the plate boundary between the oceanic crust of the philippine sea plate and the lower crust of the eurasian plate by the high pore fluid pressure caused by the fluid dehydrated from the subducting plate the existence of the high vp vs lower crust of the eurasian plate may control the occurrence of the long term slow slip events

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

ocean tide loading displacements in western europe 2 gps observed anelastic dispersion in the asthenosphere gps observed vertical ocean tide loading displacements show in cornwall southwest england and in brittany northwest france discrepancies of 2 3 mm with predicted values based on the isotropic preliminary reference earth model for the main tidal harmonic m2 yet in central europe the agreement is better than 0 5 mm by comparison of ocean tide models and validation with tide gauge observations we demonstrate that the uncertainties in the former are too small to cause this disagreement furthermore we find that different local models of the crust and different global elastic reference models derived from seismological observations can only reduce the observed discrepancies to 1 2 mm which still exceeds the gps observational uncertainty of 0 2 0 4 mm it is customary to use the elastic properties of the earth as given by seismic models previously there has been insufficient evidence to determine how to modify these properties during the transformation from seismic to tidal frequencies to account for possible anelastic dispersion in the asthenosphere and so this effect has been ignored if we include this effect then our discrepancies reduce further to 0 2 0 4 mm this value is of the same order as the sum of the remaining errors due to uncertainties in the ocean tide models and in the gps observations themselves this research provides evidence in western europe of a reduction of around 8 10 of the seismic shear modulus in the asthenosphere at tidal frequencies in addition we find that the asthenosphere absorption band frequencies can be represented by a constant quality factor q

the boso slow slip events in 2007 and 2011 as a driving process for the accompanying earthquake swarm near the boso peninsula central japan slow slip events sses accompanied by earthquake swarms repeatedly occur every 4 to 7 years we apply a network inversion filter to tilt change and global navigation satellite systems displacement data simultaneously in order to obtain the spatiotemporal slip evolution of the boso peninsula sses in 2007 and 2011 slip initiates on the eastern offshore area in both of the events and propagates to the northwestward in 2007 whereas the 2011 slip propagates to the west these slip propagations correlate well both spatially and temporally with the migration of the accompanying seismicity this indicates that the boso slow slip is a major driving process for earthquake swarm activities and that monitoring of interplate slip has the potential to be used in assessing the possibility of an earthquake in near real time

ocean tide loading displacements in western europe 1 validation of kinematic gps estimates gps has been extensively used to estimate tidal ground displacements but the accuracy of this has not been systematically verified using more than 20 sites distributed across western europe we show that postprocessed kinematic precise point positioning gps with appropriately tuned process noise constraints is capable of recovering synthetic tidal displacements inserted into real data with a typical accuracy of 0 2 mm depending on the time series noise the kinematic method does not result in erroneous propagation of signals from one coordinate component to another or to the simultaneously estimated tropospheric delay parameters it is robust to the likely effects of day to day equipment and reference frame changes and to outages in the data a minimum data span of 4 years with at least 70 availability is recommended finally we show that the method of reducing apparent coordinate time series noise by constraining the tropospheric delay to values previously estimated in static batch gps analysis in fact results in the suppression of true tidal signals using our kinematic gps analysis approach periodic displacements can be reliably observed at the 0 2 mm level which is suitable for the testing and refinement of ocean tide and solid earth response models

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

preceding coseismic and postseismic slips of the 2011 tohoku earthquake japan 1 we estimated the spatial and temporal evolution of the preceding aseismic slip from january 2003 to january 2011 the coseismic slip of the tohoku earthquake and the postseismic slip after the earthquake based on global positioning system gps data time dependent analysis indicates aseismic slip offshore of miyagi and fukushima prefectures from 2004 associated with a series of subduction earthquakes that overlap the aseismic slip area these preceding aseismic and coseismic slip areas are centered between the centers of the coseismic and afterslip areas of the tohoku earthquake offshore of miyagi prefecture while they overlap the coseismic and afterslip areas of the tohoku earthquake off fukushima prefecture the timing of moment magnitude nine mw9 class earthquakes appears to be controlled by multiple preceding slip events smaller earthquakes and their afterslip the preceding aseismic and coseismic slip decreased the coupling rate off the tohoku coast suggesting the possibility that the preceding slip represented a precursive stage of the tohoku earthquake the afterslip of the tohoku earthquake occurred in an area where the coseismic slip was not large complementing the large coseismic slip zone the afterslip along iwate miyagi extends up to 80 km in depth and is currently the sole mechanism of strain release in this depth range the source region of the anticipated miyagi oki earthquake shows small postseismic slip after the tohoku earthquake reflecting the energy release at the time of the earthquake aftershock activity is roughly governed by an afterslip process

slow slip events in the early part of the earthquake cycle in february 2014 a mw 7 0 slow slip event sse took place beneath the nicoya peninsula costa rica this event occurred 17 months after the 5 september 2012 mw 7 6 earthquake and along the same subduction zone segment during a period when significant postseismic deformation was ongoing a second sse occurred in the middle of 2015 21 months after the 2014 sse and 38 months after the earthquake the recurrence interval for nicoya sses was unchanged by the earthquake however the spatial distribution of slip for the 2014 event differed significantly from previous events having only deep 40 km slip compared to previous events which had both deep and shallow slip the 2015 sse marked a return to the combination of deep plus shallow slip of preearthquake sses however slip magnitude in 2015 was nearly twice as large mw 7 2 as preearthquake sses we employ coulomb failure stress change modeling in order to explain these changes stress changes associated with the earthquake and afterslip were highest near the shallow portion of the megathrust where preearthquake sses had significant slip lower stress change occurred on the deeper parts of the plate interface perhaps explaining why the deep 40 km region for sses remained unchanged the large amount of shallow slip in the 2015 sse may reflect lack of shallow slip in the prior sse these observations highlight the variability of aseismic strain release rates throughout the earthquake cycle

propagation of an earthquake triggering front from the 2011 tohoku oki earthquake 1 increases in seismicity have been widely observed at varying distances from the source area following large earthquakes the increased number of earthquakes are usually called aftershocks if the area is within a rupture length of the mainshock and called remotely triggered events if they are well beyond that distance these earthquakes can be explained as being induced by static and or dynamic stress changes due to the mainshock however clear observations of dynamic triggering have been inadequate to differentiate between the two mechanisms this study shows that early post seismic events triggered by the 2011 mw 9 0 tohoku oki earthquake systematically propagated over japan in a southwestern direction associated with the strong seismic waves from the source the propagation front was consistent with the arrivals of large amplitude surface waves traveling at 3 1 to 3 3 km s and extending to a distance of 1 350 km there were no observations of triggered earthquakes in the northern direction dynamic stress changes toward the north were comparable to or smaller than those necessary for triggering in the southwestern direction static stress changes were one to two orders smaller than dynamic stress changes at remote distance indicating that static stress was not the main mechanism of the triggering furthermore the dynamic stress strain changes play an important role for remote triggering if the value is more than 500 kpa in stress or 10 6 in strain

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

spatiotemporal variations of the slow slip event between 2008 and 2013 in the southcentral alaska subduction zone we apply a kalman filter based time dependent slip inversion method to model a long term slow slip event sse in the southcentral alaska subduction zone from 2008 to 2013 this event occurred downdip of the asperity that ruptured in the 1964 earthquake the same part of plate interface that slipped during a previous sse between 1998 and 2001 most of the slip deficit that accumulated during the steady period between 2001 and 2008 8 years total in the sse source region was released by this sse our results indicate both lateral and downdip propagation during this event the sse started at the end of 2008 at the upper section of the slip patch and gradually propagated to the east and to the deeper part of the interface our results indicate no connection between this sse in upper cook inlet and another sse in lower cook inlet that started in 2010 analysis of the earthquake catalog in the southcentral alaska subduction zone shows a clear increase in seismicity associated with the 2008 2013 sse with the data from a newly available continuous gps site we now can better constrain the start time of the 1998 2001 sse as 1998 58

global variations of stress drop for moderate to large earthquakes 1 we investigate the global variation of earthquake stress drops using spectra of about 2000 events of mb 5 5 between 1990 and 2007 we use an iterative least squares method to isolate source displacement spectra from travel path and receiver contributions based on a convolutional model the observed p wave source spectra are corrected with a globally averaged empirical correction spectrum and estimates of near source attenuation assuming a brune type source model we estimate corner frequencies and compute stress drops stress drop estimates for individual earthquakes range from about 0 3 to 50 mpa but the median stress drop of about 4 mpa does not vary with moment implying earthquake self similarity over the mw 5 2 to 8 3 range of our data a comparison of our results with previous studies confirms this observation over most of the instrumentally observable magnitude range while the absolute values of our estimated stress drops depend upon the assumed source model we identify relative regional variations of stress drop that are robust with respect to the processing parameters and modeling assumptions which includes an inherent assumption of constant rupture velocity we find a dependence of median stress drop on focal mechanism with a factor of 3 5 times higher stress drops for strike slip earthquakes and also find a factor of 2 times higher stress drops for intraplate earthquakes compared to interplate earthquakes

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

estimation of interplate coupling in the nankai trough japan using gps data from 1996 to 2006 we used three component surface velocities in southwest japan to estimate plate coupling on the subducting plate interface at the nankai trough we analyzed continuous gps data from the japanese geonet network from 1996 to 2006 using a consistent analysis strategy that generates bias fixed solutions for the entire network we applied systematic time series analysis methods to estimate common mode error which improved position solutions for the entire network to allow for differences in regional deformation sources we modelled the plate coupling on the plate interface beneath shikoku island to kii peninsula and the tokai suruga trough separately the results show strong coupling at a depth of 10 30 km off shikoku and kii peninsula the spatial variation in plate coupling coincides well with the coseismic rupture zones of the past large earthquakes maximum slip deficit rates of 2 3 cm yr 1 at the depth of 5 25 km are found beneath the tokai area consistent with results from other studies the downdip limits of the highly coupled areas and transition zones beneath shikoku and the kii peninsula correspond approximately to estimates of the 450 c isotherms good correlation is observed between the lateral variations of the slip deficit distribution low frequency earthquakes and coseismic slip this correlation suggests that temperature and possibly fluid variations contribute to such correlation in space the interplate slip deficit derived from the gps velocities over the 10 yr of observations is generally compatible with the results over shorter time spans suggesting that plate coupling in sw japan does not change significantly over the period of these gps measurements

temperature distribution of the upper surface of the subducted philippine sea plate along the nankai trough southwest japan from a three dimensional subduction model relation to large interplate and low frequency earthquakes summary the nankai subduction fault in southwest japan is a plate boundary along which large megathrust earthquakes have repeatedly occurred a previous 2 d thermal model suggested that the updip and downdip limits of the seismogenic zone are closely related to the temperature of the plate interface we estimated a new temperature distribution for the plate interface based on a 3 d thermal convection model that incorporates revised governing equations temporal changes in relative plate motion the shape of the subducted slab temperature variations related to basin evolution and more heat flow data and model regions than have been used in previous models the margin parallel spatial variation in the temperature of the plate interface was caused by spatio temporal changes associated with the cooling of the shikoku basin the updip limit of the thermally delineated seismogenic zone thermal seismogenic zone was approximately parallel to the trough axis due to a spreading rate that increased with distance from a fossil ridge although the margin parallel age dependency of the subducting plate was taken into account the downdip limit of the thermal seismogenic zone was determined by temperature except in eastern kyushu where it was determined by a boundary between the continental moho depth and the upper surface of the subducting plate the maximum coseismic slip associated with the 1944 tonankai m 7 9 and the 1946 nankai m 8 0 earthquakes and a strongly coupled region estimated from gps data inversion obtained by previous studies were both located in the thermal seismogenic zone on the plate interface low frequency earthquakes located at the downdip of the thermal seismogenic zone took place at temperatures of about 400 500 c this may be related to the phase transformation of hydrous minerals in oceanic crust from lawsonite blueschist jadeite to amphibole eclogite and the associated decreases in water content of approximately 2 4 wt the thermal seismogenic zone is narrowest off the kii peninsula where the hypocentres of the tonankai and nankai earthquakes were located the narrow seismogenic zone may have determined the rupture initiation points for these earthquakes as was previously demonstrated by numerical simulations of the earthquake cycle

the tidal displacement field at earth s surface determined using global gps observations 1 we investigate the 3 d tidal displacement field on earth s surface recorded globally by 456 continuous global positioning system gps stations of igs spanning 1996 2011 for eight principal diurnal and semidiurnal tidal constituents in phase and quadrature amplitudes of the residual tidal displacements after removal of an a priori body tide model are estimated using the precise point positioning ppp technique on the daily gps data the resultant daily estimates are combined to derive final estimates for each tide at each station the results are compared with the predictions of eight recent global ocean tide models separately for coastal 307 and inland 149 stations we show that gps can provide tidal displacement estimates accurate to the level of 0 12 mm horizontal and 0 24 mm vertical for the lunar only constituents m2 n2 o1 and q1 and less favorably for solar related tidal constituents s2 k2 k1 and p1 although improved by ambiguity resolution most recent ocean tide models fit the gps estimates equally well on the global scale but do not agree well between them in certain coastal areas especially for the vertical displacements suggesting the existence of model uncertainties near shallow seas the tidal residuals for the inland stations after removing both body tides and ocean tidal loading otl furthermore show clear continental scale spatial coherence implying deficiencies of the a priori body tide modeling in catching lateral heterogeneity in elastic as well as inelastic properties in the earth s deep interior we assert that the gps tidal displacement estimates now achieve sufficient accuracy to potentially provide constraints on the earth s structure

tsunamigenic potential of the shallow subduction plate boundary inferred from slow seismic slip at subduction zones slip along the shallowest parts of the plate boundary is generally thought to be aseismic observations of very low frequency earthquakes occurring at shallow levels on the plate boundary of the nankai trough subduction zone imply that slow but seismic slip can occur there and could potentially generate tsunamigenic earthquakes

probing asthenospheric density temperature and elastic moduli below the western united states periodic ocean tides continually provide a cyclic load on earth s surface the response to which can be exploited to provide new insights into earth s interior structure we used geodetic observations of surface displacements induced by ocean tidal loads to constrain a depth dependent model for the crust and uppermost mantle that provides independent estimates of density and elastic moduli below the western united states and nearby offshore regions our observations require strong gradients in both density and elastic shear moduli at the top and bottom of the asthenosphere but no discrete structural discontinuity at a depth of 220 kilometers the model indicates that the asthenosphere has a low density anomaly of 50 kilograms per cubic meter a temperature anomaly of 300 c can simultaneously explain this density anomaly and inferred colocated minima in elastic moduli

the sensitivity of surface mass loading displacement response to perturbations in the elastic structure of the crust and mantle surface mass loads generate a rich spectrum of deformation responses in the solid earth that might be exploited to probe the material properties of the crust and mantle here we present a detailed examination of load induced surface displacements and their sensitivities to systematic perturbations in elastic earth structure we compute love numbers and displacement load green s functions lgfs by integrating the equations of motion for spheroidal deformation of a radially heterogeneous and self gravitating earth sensitivity kernels are derived for individual love numbers numerically using finite differences and quasi analytically using calculus of variations we then generate sensitivity kernels for displacement lgfs by systematically perturbing the preliminary reference earth model we find that displacement lgfs are most sensitive to elastic structural perturbations within 500 km depth from the surface and for short source receiver distances for separate perturbations to the shear modulus bulk modulus and density within the crust and mantle the sensitivity kernels exhibit unique patterns consistent with the possibility to constrain the parameters independently given a spatially distributed set of sufficiently accurate loading response observations the sensitivity to density structure however is generally weak in comparison to elastic structure we also examine the sensitivity of surface displacements caused by m 2 ocean tidal loading otl to systematic perturbations in the elastic moduli and density since otl induced surface displacements are load and site dependent we focus on high resolution profiles across iceland as a case study the sensitivity kernels constitute a key element in the formulation of the inverse problem with application to geodetic tomography

repeated large slow slip events at the southcentral alaska subduction zone abstract we identify and study an ongoing slow slip event sse in the southcentral alaska subduction zone using gps measurements this is the second large sse in this region since modern geodetic measurements became available in 1993 we divide the ongoing sse into two phases according to their transient displacement time evolution their slip distributions are similar to each other but slip rates are slightly different this ongoing sse occurs downdip of the main asperity that ruptured in the 1964 alaska earthquake on the same part of the subduction interface as the earlier 1998 2001 sse the average slip rate of this sse is 4 5 cm yr with a cumulative moment magnitude of mw 7 5 mw 7 3 and mw 7 1 for phases i and ii respectively through the end of 2012 the time and space dependence of the gps displacements suggest that the slip area remained nearly the same during phase i while the slip rate increased with time the sses occur on a transitional section of the subduction plate interface between the fully locked updip part and the freely slipping deeper part during the 1964 earthquake slip on the region of the sse was much lower than slip in the updip region based on this observation and the repeated sses we conclude that this part of the interface slips repeatedly in sses throughout the interseismic period and does not build up a large slip deficit to be released through large slip in earthquakes

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

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

a new test of earth tide models in central europe new improved ocean tide models allow a corresponding improvement in ocean tide loading computations during recent years various groups have made more accurate tidal gravity observations in central europe using gravimeters carefully calibrated on various calibration lines this progress with tidal gravity measurements and ocean loading corrections now allows a more comprehensive test of body tide models than was possible previously it is shown that the o1 and m2 gravimetric factors corrected using the latest ocean tide models are very consistent between the sites despite the different instruments and gravity calibration lines that have been used these observations allow constraints to be put on the anelasticity of the earth at tidal frequencies the corrected gravimetric factors are consistent with recent model results for both the elastic prem model and with 0 09 for an anelastic prem model with the q for dissipation in shear varying as frequency to the power

strain release at the trench during shallow slow slip the example of nicoya peninsula costa rica the near trench behavior of subduction megathrust faults is critical for understanding earthquake hazard and tsunami generation the shallow subduction interface is typically located in unconsolidated sediments that are considered too weak to accumulate elastic strain however the spectrum of shallow fault slip behavior is still elusive due in large part to the lack of near field observations here we combine measurements from seafloor pressure sensors near the trench and an onshore gps network in a time dependent inversion to image the initiation and migration of a well documented slow slip event sse in 2007 at the nicoya peninsula costa rica our results show that the shallow sse initiated on the shallow subduction interface at a depth of 15 km where pore fluid pressure is inferred to be high and propagated all the way to the trench the migrating event may have triggered a second subevent that occurred one month later our results document release of elastic strain at the shallow part of the subduction megathrust and suggest prior accumulation of elastic strain in conjunction with near trench shallow slow slip recently reported for the hikurangi subduction zone and trench breaching ruptures revealed in some large earthquakes our results suggest that near trench strain accumulation and release at the shallower portions of the subduction interface is more common than previously thought

intense interface seismicity triggered by a shallow slow slip event in the central ecuador subduction zone we document a 1 week long slow slip event sse with an equivalent moment magnitude of 6 0 6 3 which occurred in august 2010 below la plata island ecuador south of the rupture area of the 1906 mw 8 8 megathrust earthquake gps data reveal that the sse occurred at a depth of about 10 km within the downdip part of a shallow 15 km isolated locked patch along the subduction interface the availability of both broadband seismometer and continuous geodetic station located at the la plata island 10 km above the sse enables a careful analysis of the relationships between slow and rapid processes of stress release along the subduction interface during the slow slip sequence the seismic data show a sharp increase of the local seismicity with more than 650 earthquakes detected among which 50 have a moment magnitude between 1 8 and 4 1 however the cumulative moment released through earthquakes accounts at most for 0 2 of the total moment release estimated from gps displacements most of the largest earthquakes are located along or very close to the subduction interface with focal mechanism consistent with the relative plate motion while the earthquake sizes show a classical distribution gutenberg richter law with a b value close to 1 the space time occurrence presents a specific pattern first the largest earthquakes appear to occur randomly during the slow slip sequence which further evidence that the seismicity is driven by the stress fluctuations related to aseismic slip moreover the seismicity observed during the sse consists in individual events and families of repeating earthquakes these observations indicate that the stress increment induced by the episodic aseismic slip may lead both to sudden seismic moment release and to progressive rupture within small locked patches this study offers an a posteriori interpretation of the seismogenesis in the central ecuador subduction zone where intense seismic swarms have been regularly observed 1977 1998 2002 and 2005 these swarms have likely been triggered by large magnitude slow slip events

spatiotemporal evolution of aseismic interplate slip between 1996 and 1998 and between 2002 and 2004 in bungo channel southwest japan 1 interplate aseismic slip in the bungo channel area southwest japan occurred during 1996 1998 and 2002 2004 we employed a square root information filter following the time dependent inversion technique to time series of daily coordinates of global positioning system gps sites the results show that aseismic interplate slip occurred beneath the southwestern part of shikoku island from late 1996 then shifted southwestward to the bungo channel area from may 1997 to february 1998 and subsided over time with a moment magnitude mw of 7 1 in contrast the 2002 2004 event shows slip in the area beneath the bungo channel in an early stage from march 2003 to august 2003 from august 2003 to january 2004 the slip area expanded by around 30 km northeastward to the southwestern part of shikoku island and the northern part of the bungo channel and then decayed over time with mw reaching 7 1 in the 2002 2004 event the start of the northeastward expansion and acceleration of the aseismic slip coincided with the occurrence of a short term slow slip event and low frequency earthquakes in a deep area this is a different spatiotemporal evolution from that of the 1996 1998 event despite having occurred in almost the same area with similar moment magnitudes a balance of slip deficit and forward aseismic slip on the plate boundary suggests that part of the bungo channel area releases strain energy mainly by episodic long term slow slip events

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

an integrated perspective of the continuum between earthquakes and slow slip phenomena slow slip a mechanism by which faults can relieve stress was thought to be distinct from earthquakes however a global review of slow slip phenomena suggests that instead there is a continuum between the two types of event

validation of ocean tide models around antarctica using onshore gps and gravity data 1 ocean tide models around antarctica are presently only sparsely tested against independent data ocean tide modeling errors along with subsequent ocean tide loading otl displacement modeling errors alias into altimetry and time variable gravity e g gravity recovery and climate experiment grace time series for example to validate various ocean tide models around antarctica gps data from 15 sites have been used to derive three dimensional displacement estimates at eight diurnal and semidiurnal tidal frequencies using hundreds of days of gps data harmonic parameters were estimated on a daily basis then combined these were then compared with otl displacement estimates derived from global and regional ocean tide models in east antarctica where the tides are well defined submillimeter differences are demonstrated in each coordinate component with the lunar n2 and q1 constituents in closest agreement as found in other studies k1 and especially k2 agree less well the spatial variation in the misfits for these two constituents indicates a site dependency with the k2 errors also suggesting an interaction with satellite dependent effects in west antarctica where sites are nearer the largest ice shelves agreement with the older models csr3 and tpxo 2 and nao 99b is poor for all constituents modeled tidal gravity variations were also compared with gravity measurements at the south pole overall the gps and gravity data agree best with newer tide models namely tpxo 6 cada00 10 fes99 and cats02 01 however validation data are lacking at the southern extents of the large ice shelves and hence some uncertainty still exists in all ocean tide models in these regions