enhanced terrestrial weathering runoff and surface ocean carbonate production during the recovery stages of the paleocene eocene thermal maximum 1 the carbonate saturation profile of the oceans shoaled markedly during a transient global warming event known as the paleocene eocene thermal maximum petm circa 55 ma the rapid release of large quantities of carbon into the ocean atmosphere system is believed to have triggered this intense episode of dissolution along with a negative carbon isotope excursion cie the brevity 120 220 kyr of the petm reflects the rapid enhancement of negative feedback mechanisms within earth s exogenic carbon cycle that served the dual function of buffering ocean ph and reducing atmospheric greenhouse gas levels detailed study of the petm stratigraphy from ocean drilling program site 690 weddell sea reveals that the cie recovery period which postdates the cie onset by 80 kyr is represented by an expanded 2 5 m thick interval containing a unique planktic foraminiferal assemblage strongly diluted by coccolithophore carbonate collectively the micropaleontological and sedimentological changes preserved within the cie recovery interval reflect a transient state when ocean atmosphere chemistry fostered prolific coccolithophore blooms that suppressed the local lysocline to relatively deeper depths a prominent peak in the abundance of the clay mineral kaolinite is associated with the cie recovery interval indicating that continental weathering runoff intensified at this time as well robert and kennett 1994 such parallel stratigraphic changes are generally consonant with the hypothesis that enhanced continental weathering runoff and carbonate precipitation helped sequester carbon during the petm recovery period e g dickens et al 1997 zachos et al 2005

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

shallow creep along the 1999 izmit earthquake rupture turkey from gps and high temporal resolution interferometric synthetic aperture radar data 2011 2017 characterizing the spatiotemporal evolution of creep is essential to constrain fault slip budget and understand creep mechanism studies based on interferometric synthetic aperture radar and global positioning system gps satellite observations until 2012 have shown that the central segment of the 17 august 1999 mw 7 4 izmit earthquake on the north anatolian fault began slipping aseismically following the event in the present study we combine new interferometric synthetic aperture radar time series based on terrasar x and sentinel 1a b radar images acquired over the period 2011 2017 with near field gps measurement campaigns performed every 6 months from 2014 to 2016 the mean velocity fields reveal that creep on the central segment of the 1999 izmit fault rupture continues to decay more than 19 years after the earthquake in overall agreement with models of postseismic afterslip decaying logarithmically with time for a long period of time along the fault section that experienced supershear velocity rupture during the izmit earthquake creep continues with a rate up to 8 mm year a significant transient accelerating creep is detected in december 2016 on the sentinel 1 time series near the maximum creep rate location associated with a total surface slip of 10 mm released in 1 month only additional analyses of the vertical velocity fields show a persistent subsidence on the hanging wall block of the golcuk normal fault that also ruptured during the izmit earthquake our results demonstrate that afterslip processes along the north anatolian fault east southeast of istanbul are more complex than previously proposed as they vary spatiotemporally along the fault

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

moment release rate of cascadia tremor constrained by gps 1 a comparison of gps and seismic analyses of 23 distinct episodic tremor and slip events located throughout the cascadia subduction zone over an 11 year period yields a highly linear relationship between moment release as estimated from gps and total duration of nonvolcanic tremor as summed from regional seismic arrays the events last 1 5 weeks typically produce 5 mm of static forearc deformation and show cumulative totals of tremor that range from 40 to 280 h moment released by each event is estimated by inverting gps measured deformation which is sensitive to all rates of tremor synchronous faulting including aseismic creep for total slip along the north american juan de fuca plate interface tremor which is shown to be largely invariant in amplitude and frequency content both between events and with respect to its duration is quantified using several different parameterizations that agree to within 10 all known cascadia events detected since 1997 which collectively span the cascadia arc from northern california to vancouver island canada release moment during tremor at a rate of 5 2 0 4 1016 n m per hour of recorded tremor this relationship enables estimation of moment dissipation via seismic monitoring of tremor along the deeper cascadia subduction zone that poses the greatest threat to its major metropolitan centers

geodetic imaging of plate motions slip rates and partitioning of deformation in japan 1 interseismic deformation in japan results from the combined effects of tectonic processes including rotation of crustal blocks and the earthquake cycle process of elastic strain accumulation about upper plate faults and subduction zone interfaces we use spherical linear block theory constrained by geodetic observations from densely spaced global positioning system gps stations to estimate plate motions fault slip rates and spatially variable interplate coupling on the japan kuril sagami and nankai subduction zones the reference model developed in this paper consists of 20 blocks produces a mean residual velocity magnitude of 1 84 mm yr at 950 stations and accounts for 96 of the observed interseismic deformation signal we estimate fault slip rates in excess of 15 mm yr along the niigata kobe tectonic zone and itoigawa shizuoka tectonic line through central japan confirming their hypothesized roles as major tectonic boundaries oblique convergence across the nankai trough is partitioned with 3 4 of the 30 mm yr of trench parallel motion accommodated by strike slip motion on the subduction interface and the remaining 1 4 accommodated by right lateral slip on the median tectonic line in contrast our models suggest negligible slip partitioning in eastern hokkaido where oblique slip on the japan kuril subduction interface accommodates all of the trench parallel component of relative plate motion inferred spatial variations in the rake and magnitude of slip deficit on subduction zone interfaces reflect the influences of megathrust geometry and earthquake cycle processes such as enhanced elastic strain accumulation about seismic asperities and coseismic sense fault motion indicative of silent slip events or afterslip following large earthquakes

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

global positioning system gps and gps acoustic observations insight into slip along the subduction zones around japan the global positioning system gps is one of the most powerful tools available for observation of earth s surface deformation in particular coseismic postseismic slow transient and interseismic deformation have all been observed globally by gps over the past two decades especially in subduction zones moreover gps acoustic techniques have been developed for practical use in the past decade allowing observation of offshore deformation immediately above slip regions here we describe the application of gps and gps acoustic observations to the detection of deformation due to plate boundary slip for interplate earthquakes as well as afterslip and slow slip events in subduction zones around japan where geodetic data coverage is particularly dense the data demonstrate temporally variable strain accumulation in the source region of the 2011 mw 9 0 tohoku oki earthquake and observation of the huge slip of the tohoku oki earthquake near the trench using gps acoustic methods has considerably advanced o

a tremor and slip event on the cocos caribbean subduction zone as measured by a global positioning system gps and seismic network on the nicoya peninsula costa rica in may 2007 a network of global positioning systems gps and seismic stations on the nicoya peninsula of northern costa rica recorded a slow slip event accompanied by seismic tremor the close proximity of the nicoya peninsula to the seismogenic part of the cocos caribbean subduction plate boundary makes it a good location to study such events several centimeters of southwest motion were recorded by the gps stations over a period of several days to several weeks and the seismic stations recorded three distinct episodes of tremor during the same time span inversion of the surface displacement data for the depth and pattern of slip on the plate interface shows peak slip at a depth of 25 30 km downdip of the main seismogenic zone estimated temperatures here are 250 300 c lower than in other subduction zones where events of this nature have been previously identified there may also be a shallower patch of slip at 6 km depth these results are significant in that they are the first to suggest that slow slip can occur at the updip transition from stick slip to stable sliding and that a critical temperature threshold is not required for slow slip tremor and low frequency earthquake locations are more difficult to determine our results suggest they occur on or near the plate interface at the same depth range as the deep slow slip but not spatially colocated

along strike variations in short term slow slip events in the southwest japan subduction zone 1 short term slow slip events accompanied by nonvolcanic deep low frequency tremors and deep very low frequency earthquakes in southwest japan were investigated systematically by means of ground tilting studies the change in tilt usually lasts for several days by using a genetic algorithm and a least squares method we inverted the data for tilt steps that were caused by slow slip events and were detected by at least four stations situated near the source of the tremor fault parameters were estimated for 54 slow slip episodes that occurred mainly in the western shikoku northeastern kii and tokai regions from 2001 to 2008 in eastern shikoku two slow slip episodes were detected quantitatively for the first time the fault geometries of all the slow slip events were located within the belt like distribution of tremors in the transition zone between the locked and aseismic slip zones at the plate interface of the subducting philippine sea plate the spatial extent of the fault geometry corresponds roughly to the distribution of clusters of nonvolcanic tremors and very low frequency earthquakes the moment magnitudes ranged from 5 4 to 6 2 and the slip was 1 cm for each slow slip event the rate of moment release by the detected slow slip events was 40 60 of the moment accumulation expected from the relative plate motion and it showed regional differences they may reflect the along strike variations in plate convergence and or the characteristic size of the slow slip fault plane on the plate interface

slow slip rate and excitation efficiency of deep low frequency tremors beneath southwest japan abstract we estimated the long term average slip rate on the plate interface across the nankai subduction zone during 2002 2013 using deep low frequency tremors as a proxy for short term slow slip events based on empirical relations between the seismic moment of short term slow slip events and tremor activities the slip rate in each region is likely to compensate for differences between the convergence rate and the slip deficit rate of the subducting philippine sea plate estimated geodetically although the uncertainty is large this implies that the strain because of the subduction of the plate is partially stored as the slip deficit and partially released by slow slip events during the interseismic period the excitation efficiency of the tremors for the slow slip events differs among regions it is high in the northern kii region some events in the western shikoku region show a somewhat large value antigorite serpentinite of two types exists in the mantle wedge beneath southwest japan slips with more effective excitation of tremors presumably occur in high temperature conditions in the antigorite olivine stability field other slip events with low excitation efficiency are distributed in the antigorite brucite stability field considering the formation reactions of these minerals and their characteristic structures events with high excitation efficiency can be correlated with a high pore fluid pressure condition this result suggests that variation in pore fluid pressure on the plate interface affects the magnitude of tremors excited by slow slip events

detailed spatial slip distribution for short term slow slip events along the nankai subduction zone southwest japan short term slow slip events s sses intensively occur at the transition zone along the nankai subduction zone southwest japan because crustal deformation due to a single s sse is small the sour

detection of short term slow slip events along the nankai trough via groundwater observations 1 in order to develop new tools or techniques to detect short term slow slip events s sses along subduction zones we attempted to detect s sses by conducting groundwater pressure observations at ano station which is a groundwater observation station operated by the geological survey of japan the national institute of advanced industrial science and technology for earthquake prediction research groundwater pressures changed due to six s sses that occurred near ano from june 2011 to april in 2013 the fault models of these s sses which were estimated mainly by observing the crustal strains and tilts explained the changes in the groundwater pressures if the strain sensitivity of the observed groundwater pressure or level is larger than 1 mm nstrain and the noise level is smaller than 50 mm day it is possible to detect s sses that occur in southwest japan by conducting groundwater pressure or level observations

deep low frequency tremors as a proxy for slip monitoring at plate interface 1 we propose a new method to monitor slip at the plate interface using non volcanic deep low frequency dlf tremors we assume that a dlf tremor is the superposition of frequently excited intermittent events meaning that the envelope of the reduced displacement of the dlf tremor provides an apparent moment rate function we estimate a conversion factor from the apparent moment to the seismic moment with an assumption that a total size of dlf tremors of an episode is proportional to the size of corresponding slow slip event sse the cumulative seismic moment estimated by dlf tremors is consistent with that estimated from geodetic methods and provides appropriate slip and slip rate at the plate interface this proves our assumptions and demonstrates that dlf tremors are useful tool for real time monitoring of the slip at the plate interface

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

low friction and fault weakening revealed by rising sensitivity of tremor to tidal stress at subduction zones deep parts of the fault can slip slowly generating tremor analysis of tremor in cascadia reveals increasing sensitivity of slip to tidal stresses over several days implying that the fault is weak and weakens as it slips

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

a numerical simulation of earthquake cycles along the nankai trough in southwest japan lateral variation in frictional property due to the slab geometry controls the nucleation position abstract the occurrence pattern of historical great earthquakes along the nankai trough indicates the existence of rupture segments that seem to correlate with 100 km scale lateral variation in the dip angle of the subducting philippine sea plate for instance the latest earthquakes the 1944 tonankai and the 1946 nankai earthquakes initiated their ruptures off kii peninsula where the dip angle of the slab is steeper than in adjacent areas to investigate how such heterogeneity in slab geometry affects the occurrence of earthquakes we conducted a three dimensional 3d numerical simulation of earthquake cycles for a large source area about 700 km long along the trough and 300 km wide in the dip direction based on a rate and state dependent friction law we used a simple flat dipping plane to model the plate boundary frictional parameters and effective normal stress were assumed to depend on the estimated depth of the real plate boundary based on seismic surveys and seismicity data the depth dependent frictional parameters were mapped on the flat model plane this made lateral variation in frictional property due to the variation in the dip angle of the slab the plate convergence rate in the model decreased eastward along the trough consistent with a recent global positioning system gps analysis in the simulation results preslip occurred and rupture started off kii peninsula both effects of a narrower locked area due to the higher dip angle and a higher plate convergence rate caused the highest stress accumulation rate to be in this area promoting slip nucleation our simple simulation suggests that lateral variation in the dip angle of the slab is one of the factors controlling the nucleation position of great interplate earthquakes

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

modeling short and long term slow slip events in the seismic cycles of large subduction earthquakes 1 slow slip events sses occur in the deeper extents of areas where large interplate earthquakes are expected in subduction zones such as the nankai region of japan and the cascadia region of north america in the nankai region sses are divided into long and short term sses depending on their duration and recurrence interval we modeled and examined the occurrence of long and short term sses and changes in their behavior during the seismic cycles of large interplate earthquakes in these numerical simulations we adopted a rate and state dependent friction law with cutoff velocities and assumed that the distribution of pore fluid controls the recurrence interval of both long and short term sses the recurrence intervals of reproduced short term sses decrease during a long term sse as observed in western shikoku in the nankai region the recurrence intervals of both types of sses become shorter in the later stages of interseismic periods large interplate earthquakes nucleate between the region where sses occur and the locked region of the large earthquakes as suggested from observations of the 1944 tonankai earthquake our numerical results suggest that the stress buildup process in a seismic cycle affects the recurrence behavior of sses

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

crustal deformation caused by magma migration in the northern izu islands japan intense crustal activity including earthquake swarms eruptions and a caldera formation in the northern izu islands started on june 26 2000 accompanied with large crustal deformation permanent gps data reveals the spatial pattern and time evolution of ground deformation the observations reveal shrinking and subsidence of miyakejima and extension between kouzushima and niijima we constructed a source model to explain the observed displacements during the period between june 26 and the end of august the model consists of a deflation source 0 12km beneath miyakejima tensile faults 1 04km located between miyakejima and kouzushima and several shear faults mass balance considerations suggest that a large amount of magma migrated 30km from miyakejima toward kouzushima

short term slow slip and correlated tremor episodes in the tokai region central japan 1 we observe the related phenomenon of short term slow slip event sse and low frequency nonvolcanic tremor on the deeper extension of the 1944 tonankai and the anticipated tokai earthquake rupture areas central japan japan nation wide seismometer and tiltmeter array nied hi net has recorded these correlated episodes of sse and tremor known as episodic tremor and slip ets in 2004 and 2005 the events are located on two areas in the tokai region one is near the shima peninsula and the other is around the aichi area both episodes have a typical duration of 2 3 days and released seismic moment corresponding to mw 6 0 moreover these episodes repeatedly occur with a recurrence interval of about six months in both areas this evidence suggests that the coincidence between the sse and the tremor is a characteristic behavior in the whole tremor belt like zone in the nankai trough subduction zone

continuous observation of groundwater and crustal deformation for forecasting tonankai and nankai earthquakes in japan in 2006 we started construction of an observation network of 12 stations in and around shikoku and the kii peninsula to conduct research for forecasting tonankai and nankai earthquakes the purpose of the network is to clarify the mechanism of past preseismic groundwater changes and crustal deformation related to tonankai and nankai earthquakes construction of the network of 12 stations was completed in january 2009 work on two stations hongu mikoshi hgm and ichiura icu was finished earlier and they began observations in 2007 these two stations detected strain changes caused by the slow slip events on the plate boundary in june 2008 although related changes in groundwater levels were not clearly recognized

split philippine sea plate beneath japan 1 the shape of the philippine sea plate subducting beneath western japan is a crucial factor in understanding earthquakes and volcanic activity we propose that the subducted plate was split along an extinct ridge due to an abrupt change of subduction direction followed by elastic deformation of the plate and an accumulation of stress near the ridge this shape is consistent with receiver function images the distribution of deep tremor sources the seismicity and focal mechanisms of intraplate earthquakes and the distribution of anomalous ratios of helium isotopes in ground water the movement history of the plate can explain active tectonics in western japan in the last 2 4 ma the location history of the volcanic front and the tear control where fluids ascend in the crust and these fluids are responsible for the generation of large earthquakes and volcanoes

depth dependent activity of non volcanic tremor in southwest japan 1 with a new location method we obtained a high resolution map of non volcanic tremor along the subducting philippine sea plate in southwest japan and clarified the depth dependent behavior of the tremor activity a bimodal distribution of tremor along dip is apparent in regions where short term slow slip events sses and very low frequency earthquakes are frequently detected the separation of bimodal peaks is 5 to 10 km in depth the updip tremor activity occurs episodically coincident with major bursts that often accompany geodetically detectable sses the downdip tremor activity is however rather stable with frequent minor bursts this depth dependent tremor activity likely reflects variation of interplate slip properties specifically weakening with increasing depth and temperature in westernmost shikoku anomalous tremor activity was detected in only the updip section in late 2003 this is interpreted as being triggered by a long term sse in the shallower edge of the tremor zone

future cascadia megathrust rupture delineated by episodic tremor and slip 1 a suite of 15 episodic tremor and slip events imaged between 1997 and 2008 along the northern cascadia subduction zone suggests future coseismic rupture will extend to 25 km depth or 60 km inland of the pacific coast rather than stopping offshore at 15 km depth an ets derived coupling profile accurately predicts gps measured interseismic deformation of the overlying north american plate as measured by 50 continuous gps stations across western washington state when extrapolated over the 550 year average recurrence interval of cascadia megathrust events the coupling model also replicates the pattern and amplitude of coseismic coastal subsidence inferred from previous megathrust earthquakes here for only the washington state segment of the cascadia margin this translates into an mw 8 9 earthquake with significant moment release close to its metropolitan centers

m w dependence of the preseismic ionospheric electron enhancements ionospheric electron enhancement was reported to have occurred 40 min before the 2011 tohoku oki mw9 0 earthquake japan by observing total electron content tec with global navigation satellite systems receivers their reality has been repeatedly questioned due mainly to the ambiguity in the derivation of the reference tec curves from which anomalies are defined here we propose a numerical approach based on akaike s information criterion to detect positive breaks sudden increase of tec rate in the vertical tec time series without using reference curves we demonstrate that such breaks are detected 25 80 min before the eight recent large earthquakes with moment magnitudes mw of 8 2 9 2 the amounts of precursory rate changes were found to depend upon background tec as well as mw the precursor times also showed mw dependence and the precursors of intraplate earthquakes tend to start earlier than interplate earthquakes we also performed the same analyses during periods without earthquakes to evaluate the usefulness of tec observations for short term earthquake prediction

the slow earthquake spectrum in the japan trench illuminated by the s net seafloor observatories investigating slow earthquake activity in subduction zones provides insight into the slip behavior of megathrusts which can provide important clues about the rupture extent of future great earthquakes using the s net ocean bottom seismograph network along the japan trench we mapped a detailed distribution of tectonic tremors which coincided with very low frequency earthquakes and a slow slip event compiling these and other related observations including repeating earthquakes and earthquake swarms we found that the slow earthquake distribution is complementary to the tohoku oki earthquake rupture we used our observations to divide the megathrust in the japan trench into three along strike segments characterized by different slip behaviors we found that the rupture of the tohoku oki earthquake which nucleated in the central segment was terminated by the two adjacent segments

slab dehydration in warm subduction zones at depths of episodic slip and tremor abstract non volcanic tremor nvt and episodic slow slip events sses have been observed below the seismogenic zone of relatively warm subduction zones for the past 20 years geophysical and geologic observations show that this portion of the subduction interface is fluid rich and many models for these slip behaviors necessitate high pore fluid pressures however whether these fluids are sourced from local dehydration reactions in particular lithologies or require up dip transport from greater depths is not known we present thermodynamic models of the petrologic evolution of four lithologies typical of the plate interface average morb seafloor altered morb hydrated depleted morb mantle and metapelite along predicted plate boundary pressure temperature p t paths at several warm subduction segments where nvt and sses are observed at depths between 25 65 km the models suggest that 1 2 wt h2o is released at the depths of nvt sses in jalisco colima guerrero cascadia and shikoku due to punctuated dehydration reactions within morb primarily through chlorite and or lawsonite breakdown these reactions produce sufficient in situ fluid across a narrow p t range to cause high pore fluid pressures at nvt sse depths dehydration of hydrated peridotite is minimal at these depths for most margins and metapelite releases h2o

detection of short term slow slip events along the nankai trough southwest japan using gnss data 1 we detected short term slow slip events sses previously observable only with tilt and strain data along the nankai trough southwest japan using gnss global navigation satellite system data offsets detected in gnss time series using akaike s information criterion helped automatically identify 207 episodes with a motion direction opposite to that of the relative plate motion from june 1996 to january 2012 by nonlinear inversion of the detected displacement we estimated rectangular fault models for 133 probable and 25 possible short term sses over 15 years the sse moment magnitudes range from 5 5 to 6 3 most sse fault models are located in a narrow band of non volcanic tremors on the interfaces of the subducting philippine sea plate large sses moment magnitude mw 6 often occur in western and central shikoku the cumulative slip is distributed heterogeneously along the strike generally decreasing eastward with the maximum slip 50 cm in western shikoku no definite short term sses were found in the kii channel but several short term sses occurred in ise bay both regions are known as tremor gaps the local maximum of the cumulative slip fills in the tremor gap located in ise bay the long term rate of short term sse cumulative moment increased by threefold around 2003 in eastern shikoku whereas it was almost constant in other regions comparison with short term sse catalogues using tilt data suggests that both this study and previous studies missed some sses along the nankai trough a combination of geodetic data is important in the monitoring of the spatiotemporal distribution of short term sses

slow slip phenomena in cascadia from 2007 and beyond a review recent technological advances combined with more detailed analyses of seismologic and geodetic observations have fundamentally changed our understanding of the ways in which tectonic stresses arising from plate motions are accommodated by slip on faults the traditional view that relative plate motions are accommodated by a simple cycle of stress accumulation and release on locked plate boundary faults has been revolutionized by the serendipitous discovery and recognition of the significance of slow slip phenomena mostly in the deeper reaches of subduction zones the cascadia subduction zone located in the pacific northwest of the conterminous united states and adjacent canada is an archetype of exploration and learning about slow slip phenomena these phenomena are manifest as geodetically observed aseismic transient deformations accompanied by a previously unrecognized class of seismic signals although secondary failure processes may be involved in generating the seismic signals the primary origins of both aseismic and seismic phenomena appear to be episodic fault slip probably facilitated by fluids on a plate interface that is critically stressed or weakened in cascadia this transient slip evolves more slowly and over more prolonged durations relative to the slip in earthquakes and it occurs between the 30 and 40 km depth contours of the plate interface where information was previously elusive although there is some underlying organization that relaxes nearly all the accrued plate motion stresses along the entirety of cascadia we now infer that slow slip evolves in complex patterns indicative of propagating stress fronts our new understanding provides key constraints not only on the region where the slow slip originates but also on the probable characteristics of future megathrust earthquakes in cascadia herein we review the most significant scientific issues and progress related to understanding slow slip phenomena in cascadia and highlight some of their societal implications we provide a comprehensive review from the big picture as inferred from studies of regional scale monitoring data to the details revealed by innovative focused experiments and new instrumentation we focus on what has been learned largely since 2007 when several major investments in monitoring and temporary deployments dramatically increased the quality and quantity of available data

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

an integrated global model of present day plate motions and plate boundary deformation summary in this paper we present a global model gsrm 1 of both horizontal velocities on the earth s surface and horizontal strain rates for almost all deforming plate boundary zones a model strain rate field is obtained jointly with a global velocity field in the process of solving for a global velocity gradient tensor field in our model we perform a least squares fit between model velocities and observed geodetic velocities as well as between model strain rates and observed geological strain rates model velocities and strain rates are interpolated over a spherical earth using bi cubic bessel splines we include 3000 geodetic velocities from 50 different mostly published studies geological strain rates are obtained for central asia only and they are inferred from quaternary fault slip rates for all areas where no geological information is included a priori constraints are placed on the style and direction but not magnitude of the model strain rate field these constraints are taken from a seismic strain rate field inferred from normalized focal mechanisms of shallow earthquakes we present a global solution of the second invariant of the model strain rate field as well as strain rate solutions for a few selected plate boundary zones generally the strain rate tensor field is consistent with geological and seismological data with the assumption of plate rigidity for all areas other than the plate boundary zones we also present relative angular velocities for most plate pairs we find that in general there is a good agreement between the present day plate motions we obtain and longterm plate motions but a few significant differences exist the rotation rates for the indian arabian and nubian plates relative to eurasia are 30 13 and 50 per cent slower than the nuvel1a estimate respectively and the rotation rate for the nazca plate relative to south america is 17 per cent slower on the other hand caribbean north america motion is 76 per cent faster than the nuvel 1a estimate while crustal blocks in the india eurasia collision zone move significantly and self consistently with respect to bounding plates only a very small motion is predicted between the nubian and somalian plates by integrating plate boundary zone deformation with the traditional modelling of angular velocities of rigid plates we have obtained a model that has already been proven valuable in for instance redefining a no net rotation model of surface motions and by confirming a global correlation between seismicity rates and tectonic moment rates along subduction zones and within zones of continental deformation

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

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

seismic and geodetic constraints on cascadia slow slip 1 automatically detected and located tremor epicenters from episodic tremor and slip ets episodes in northern cascadia provide a high resolution map of washington s slow slip region thousands of epicenters from the past four ets events from 2004 to 2008 provide detailed map view constraints that correlate with geodetic estimates of the simultaneous slow slip each of these ets events exhibits remarkable similarity in the timing and geographic distribution of tremor density and geodetically inferred slip analysis of the latest 15 month inter ets period also reveals ageodetic tremor activity similar both in duration and extent to ets tremor epicenters from both ets and inter ets tremor are bounded between the 30 and 45 km plate interface depth contours and locate approximately 75 km east of previous estimates of the locked portion of the subducting juan de fuca plate inter ets tremor overlaps but is generally downdip of ets tremor and does not yet correlate with geodetically observed slip but this is likely because the slip is below current gps detection levels based on the tremor and slip correlation and the tremor duration and slip magnitude relationship we suggest that the well resolved sharp updip edge of tremor epicenters reflects a change in plate interface coupling properties the region updip of this boundary may accumulate stress with the potential for coseismic shear failure during a megathrust earthquake alternatively plate convergence in this region could be accommodated by continuous slow slip with no detectable tremor or by slow slip events with sufficiently long recurrence intervals that none have been detected during the past 10 years of gps observations

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 event within a gap between tremor and locked zones in the nankai subduction zone we report on two small long term slow slip events sses within a gap between tremor and locked zones in the nankai subduction zone southwest japan the sses were detected by subtracting the steady state component and postseismic effects of large earthquakes from long term and high density global navigation satellite system data both sses occurred in adjacent regions of the bungo channel following long term sses in the bungo channel in 2003 and 2010 the estimated slip was 1 5 cm year that lasted at least 1 2 years after 2004 and 2011 partly accommodating plate convergence as the low frequency tremor in the downdip region is activated at the same time as the bungo channel long term sse a spatiotemporal correlation was observed between the detected sses and long term tremor activity in the downdip region this correlation indicates along dip interaction of the slips on the subducting plate interface

characteristic silent earthquakes in the eastern part of the boso peninsula central japan 1 analysis of global positioning system gps data shows transient crustal deformation in the boso peninsula central japan for about fifty days from october 2002 the southeastward horizontal displacements detected suggest the occurrence of interplate aseismic slip between the philippine sea plate and the north american plate six years after a similar event in 1996 we estimate an area of aseismic slip with moment magnitude mw 6 6 centered off the boso peninsula adjacent to associated seismic activity slip evolution of the 2002 aeismic slip started on october 4 and migrated from north to south for about ten days followed by gradual subsidence and restarting of slip which lasted until december 2 propagating more southward similarities in focal area and slip process between the 1996 and the 2002 events suggest the boso aseismic slips as characteristic silent earthquakes together with the repetitive occurrence of seismic swarm in a similar region every six to seven years a more tightly coupled southern area that did not release enough energy in the 1996 event may have caused the differences in magnitude central slip area and duration between the 1996 and the 2002 events if the hypothesized recurrence interval for strain accumulation is true based on swarm seismicity

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

crustal motions in great britain evidence from continuous gps absolute gravity and holocene sea level data two independent continuous global positioning system cgps processing strategies based on a double difference regional network and a globally transformed precise point positioning solution provide horizontal and vertical crustal motion estimates for great britain absolute gravity and geological information from late holocene sea level data further constrain the vertical motion estimates for 40 cgps stations we estimate station velocities and associated uncertainties using maximum likelihood estimation assuming the presence of white and coloured noise horizontal station velocity estimates agree to 1 mm yr 1 between the two cgps processing strategies and closely follow predicted plate motions residual velocities generally 1 mm yr 1 follow no regular pattern that is there is no discernible internal deformation nor any dependence on station monumentation or time series length vertical station velocity estimates for the two cgps processing strategies agree to similar to 1 mm yr 1 but show an offset of similar to 1 mm yr 1 with respect to the absolute gravity ag estimates we attribute this offset to a bias related to known issues in current cgps results and correct for it by ag alignment of our cgps estimates of vertical station velocity both cgps estimates and ag aligned cgps estimates of present day vertical crustal motions confirm the pattern of subsidence and uplift in great britain derived from holocene sea level data for the last few thousand years ongoing subsidence on shetland uplift in most areas of scotland and subsidence in large areas of england and wales

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

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

continental lithospheric thickness and deglaciation induced true polar wander the secular drift of the earth s rotation pole which is evident in ils data is a memory of the planet of the last deglaciation event of the current ice age in order to fit the observed rate and direction of drift with an earth model whose viscosity profile is capable of reconciling the free air gravity and relative sea level data of postglacial rebound requires a lithospheric thickness which is substantially in excess of that which might be considered an appropriate average thickness for the entire planet this required thickness which is greater than 250 km is nevertheless in accord with independent estimates of the thickness of the continental lithosphere

transient crustal movement in the northern izu bonin arc starting in 2004 a large slow slip event or a slow back arc rifting event abstract the izu bonin arc lies along the convergent boundary where the pacific plate subducts beneath the philippine sea plate horizontal velocities of continuous global navigation satellite system stations on the izu islands move eastward by up to 1 cm year relative to the stable part of the philippine sea plate suggesting active back arc rifting behind the northern part of the arc here we report that such eastward movements transiently accelerated in the middle of 2004 resulting in 3 cm extra movements in 3 years we compare three different mechanisms possibly responsible for this transient movement i e 1 postseismic movement of the 2004 september earthquake sequence off the kii peninsula far to the west 2 a temporary activation of the back arc rifting to the west dynamically triggered by seismic waves from a nearby earthquake and 3 a large slow slip event in the izu bonin trench to the east by comparing crustal movements in different regions the first possibility can be shown unlikely it is difficult to rule out the second possibility but current evidence support the third possibility i e a large slow slip event with moment magnitude of 7 5 may have occurred there

subduction of the philippine sea plate beneath southwestern japan slab geometry and its relationship to arc magmatism 1 we carry out high resolution three dimensional seismic tomography of the crust and upper mantle beneath southwestern sw japan using arrival time data obtained from the nationwide seismograph network the tomographic images provide new insights into the configuration of the philippine sea slab and arc magmatism the results confirm the existence of an aseismic portion of the philippine sea slab at greater depths beyond the seismic portion the philippine sea slab is subducting aseismically down to at least a depth of 200 km in chubu 60 80 km in kinki and 60 km in chugoku and is subducting seismically to depths of 150 200 km in kyushu in the chubu district it is subducting seismically at a shallow dip and then bends downward beneath the volcanic area whereas in the kinki district it is subducting subhorizontally as far as the japan sea the differences in the slab geometry between adjacent regions correlate with the differences in volcanic activity suggesting the importance of the geometry of the philippine sea slab on arc magmatism our tomographic images further imply subduction of the philippine sea slab down to a depth of around 70 km northwest of the izu peninsula the philippine sea slab in that region might have split into western and eastern parts separated by a slab tear and collided with the pacific slab at depths of 150 200 km

high precision slip distribution of the 1944 tonankai earthquake inferred from tsunami waveforms possible slip on a splay fault abstract inversion of tsunami waveforms is a well established technique for estimating the slip distributions of subduction zone earthquakes with some of the most detailed results having been obtained for earthquakes in the nankai trough sw japan the present study although it uses a method and tsunami waveform data set almost identical to previous study aims to improve on previous work by using a more precise specification of initial conditions for the calculation of tsunami green s functions specifically we incorporated four improvements in the present study 1 we used a realistic plate model based only on seismic survey results and assumed it to be the fault plane of the 1944 tonankai earthquake 2 the smallest subfaults consistent with the long wavelength approximation were used in the tsunami inversion analysis 3 we included the effect of horizontal displacement of the ocean bottom on tsunami generation and 4 we performed a checkerboard resolution test as obtained in previous studies a zone of high slip 2 0 m was resolved off the shima peninsula however the more precise calculation of tsunami green s functions has revealed additional detail that was not evident in previous studies which we demonstrate is resolvable and correlates with the position of known faults in the accretionary prism while there was little or no slip near the trench axis in the eastern part of the rupture zone there was up to 1 5 m of slip resolved within 30 km of the trough axis in the western part along the coast of the kii peninsula this troughward slip zone coincides with the position of a large splay fault mapped in multichannel reflection surveys furthermore it is also clear that the upper edge of the enshu fault off shima and atsumi peninsulas is consistent with the up dip limit of slip in the eastern part of our model we tested the possibility that slip occurred on the former splay fault instead of on the plate interface during the 1944 tonankai earthquake and find that slip on this splay fault is also consistent with the data although we cannot distinguish whether slip was dominant on the splay fault or on the plate interface we further suggest that the position of the enshu fault may be determined by the subduction of topographic highs and that such faults may have an important influence on the up dip rupture limit of the 1944 tonankai and potentially other subduction zone earthquakes

slow slip evolves into megathrust earthquakes in 2d numerical simulations 1 slow slip events sse in many subduction zones incrementally stress the adjacent locked megathrust suggesting that they could potentially either trigger or evolve into damaging earthquakes we explore this with 2d quasi dynamic simulations with rate state friction dilatancy and coupled 1d pore fluid and heat transport steady state weakening friction allows transient slip to nucleate but is inhibited by dilatant strengthening and destabilized by thermal pressurization sse spontaneously nucleate in low effective stress velocity weakening lesvw regions if the dimension of the lesvw is relatively small the sse are trapped at its updip end imparting a strong stress concentration in the locked zone after several centuries sse penetrate into the region of higher effective stress where thermal pressurization eventually leads to dynamic rupture for larger lesvw regions sse tend to increase in length with time ultimately higher slip speeds enhance thermal weakening leading to dynamic instability within the sse zone in both cases the onset of the ultimate sse is essentially indistinguishable from preceding events

spatiotemporal evolution of long and short term slow slip events in the tokai region central japan estimated from a very dense gnss network during 2013 2016

southern california permanent gps geodetic array spatial filtering of daily positions for estimating coseismic and postseismic displacements induced by the 1992 landers earthquake the june 28 1992 m w 7 3 landers california earthquake was the first earthquake to be surveyed by a continuously operating global positioning system gps array the coordinate time series of seven sites are evaluated for station displacements during an interval of 100 days centered on the day of the earthquake we employ a new spatial filtering technique that removes common mode errors from the coordinate time series this approach provides precise estimates of site specific displacements compared to the cumbersome method of analyzing baselines between pairs of stations all sites indicate significant coseismic horizontal displacements of 5 65 mm with uncertainties of 1 2 mm horizontal displacements are in general agreement with elastic dislocation models in particular for sites closer to the epicenter vertical displacements range from 13 to 7 mm with uncertainties of 2 4 mm the observed vertical displacements in all cases show 5 10 mm more subsidence than expected from geodetic and seismic geologic models significant postseismic horizontal displacements totaling 6 2 mm 10 20 of the coseismic displacement are detected at the three sites closest to the epicenter these displacements are modeled as a short term exponential relaxation with a decay time of 22 10 days superimposed on a longer term linear interseismic trend scaling the observed coseismic and postseismic displacements at one of the sites with the distance to the epicenter provides a measure of site strain which agrees well with the direction and magnitude determined from more precise laser strain meter data the time series do not show any detectable preseismic displacements

automated detection of slow slip events within the nankai subduction zone 1 we have developed a new automated method for the identification and location of slow slip events sses during episodic tremor and slip ets in the nankai subduction zone without any tremor information sse models are estimated from continuous tilt data using the kalman filter algorithm and a grid search and are eventually identified through statistical evaluations we applied this method to data recorded for two years in shikoku japan and successfully detected four sses coincident with major tremor bursts before the onset of sses precursory minor tremor activities usually occur around the fault where sses are subsequently detected when tremor migrates into the sse faults this suggests that an ets episode begins with geodetically undetectable small slip around the main fault and grows to a detectable sse such evolution of sse and tremor activity would reflect the spatial change in the slip property on the plate interface

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

dissolution susceptibility of paleocene eocene planktic foraminifera implications for palaeoceanographic reconstructions abstract we investigated shell characteristics and differential dissolution susceptibility of planktic foraminiferal species derived from upper paleocene and lower eocene deep sea sequences ocean drilling program odp site 865 allison guyot and sites 1209b 1210b and 1212a shatsky rise in the north pacific ocean the purposes of this study are 1 assessing the effects of differential dissolution on upper paleocene lower eocene planktic foraminiferal assemblages at species level and within different biozones to quantify dissolution susceptibility of genera and species 2 investigating the differences in shell characteristics 3 revealing the relationship between shell parameters and dissolution robustness of taxa and 4 identifying the key shell parameter s influencing the dissolution susceptibility of foraminiferal taxa two independent experiments were carried out one focusing on gradual qualitative deterioration of taxa by dissolution and the other documenting the weight loss of taxa shell parameters such as wall thickness porosity and pore size were determined through scanning electron microscopy sem and image analysis jmicrovision we found that the large muricate acarinina and morozovella are most resistant followed by the cancellate subbotina and the small muricate igorina confirming results of previous work at species level the thick walled acarinina soldadoensis acarinina subsphaerica and the large morozovella subbotinae are the most resistant species most of the large morozovella species such as morozovella aequa morozovella formosa gracilis morozovella velascoensis and morozovella pasionensis together with acarinina nitida show intermediate dissolution resistance whereas the small muricate igorina species the cancellate subbotina velascoensis and the thin walled morozovella acuta and morozovella occlusa are the most vulnerable species we propose a formula for calculating the dissolution resistance of taxa based on their wall thickness and size two key parameters in dissolution resistance of a species application of this formula reveals good agreement between the calculated and measured dissolution resistance indicating its robustness furthermore the agreement between our experimental results in situ experimental results on live foraminifera and natural quantitative qualitative records suggests that our experiments accurately mimic natural dissolution processes consequently these experimental results strongly bear on interpretations of foraminiferal dissolution in natural environments especially in studies on early paleogene climatic events that are often associated with dissolution phenomena more generally a proper assessment of taphonomic alteration by dissolution should be part of every paleoenvironmental reconstruction based on quantitative foraminiferal records

time dependent inversion study of the slow thrust event in the nankai trough subduction zone southwestern japan we estimate time variation of interplate coupling between the subducting philippine sea and the overriding continental plates along the western part of the nankai trough japan during the period between 1996 and 1999 after subtracting annual components and average annual velocities deviation from steady crustal deformation in the shikoku and kyushu islands is examined around 15 gps stations facing the bungo channel detected the following three stage ground displacements of up to 3 cm in 1997 with a duration of 1 year 1 increased displacement rate associated with the 1996 hyuga nada earthquakes 2 an increasingly rapid anomalous period of deformation from june 1997 to the end of 1997 and 3 a slowdown period and return to normal rates of deformation after the end of 1997 linearized least squares locate the slip area of this slow event near the plate boundary beneath the bungo channel the estimated slip is opposite the motion of the philippine sea plate these results support the hypothesis that the observed anomalous caistal deformation is due to a rebound process of the philippine sea plate time dependent inversion analysis shows the following slip history during the initial period of increased displacement rate a visible slip area is resolved beneath the coastal area of southwestern shikoku in the next stage of accelerated displacements the slip area expanded southwestward to the bungo channel beginning around june 1997 when postseismic slip of the 1996 hyuga nada earthquakes almost ended after this accelerated period the estimated thrust slip ends with time

three dimensional seismic velocity structure and configuration of the philippine sea slab in southwestern japan estimated by double difference tomography 1 three dimensional seismic velocity structure in and around the philippine sea plate subducting beneath southwestern sw japan is determined by applying double difference tomography method to arrival time data for earthquakes obtained by a dense nationwide seismic network in japan a region of low s wave velocity and high vp vs of several kilometers in thickness is recognized immediately above the region of intraslab seismicity in a wide area from tokai to kyushu this characteristic layer dips shallowly in the direction of slab subduction compared with the upper surface of the philippine sea slab based on seismic reflection and refraction surveys on seven survey lines we interpret that the low vs and high vp vs layer corresponds to the oceanic crust of the philippine sea slab on the basis of the position of the low vs and high vp vs layer and the precisely relocated hypocenter distribution of intraslab earthquakes the upper surface of the philippine sea slab is reliably determined for the entire area of sw japan nonvolcanic deep low frequency earthquakes that occurred associated with the subduction of the philippine sea slab are distributed along the isodepth contour of 30 km in sw japan except for the tokai district where the depth of deep low frequency earthquakes becomes gradually deeper toward northeast

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

centroid moment tensor inversions of offshore earthquakes using a three dimensional velocity structure model slip distributions on the plate boundary along the nankai trough due to complex three dimensional 3d heterogeneous structures conventional one dimensional 1d analysis techniques using onshore seismograms can yield incorrect estimation of earthquake source parameters especially dip angles and centroid depths of offshore earthquakes combining long term onshore seismic observations and numerical simulations of seismic wave propagation in a 3d model we conducted centroid moment tensor cmt inversions of earthquakes along the nankai trough between april 2004 and august 2019 to evaluate decade scale seismicity green s functions for cmt inversions of earthquakes with moment magnitudes of 4 3 6 5 were evaluated using finite difference method simulations of seismic wave propagation in the regional 3d velocity structure model significant differences of focal mechanisms and centroid depths between previous 1d and our 3d catalogues were found in the solutions of offshore earthquakes by introducing the 3d structures of the low velocity accretionary prism and the philippine sea plate dip angles and centroid depths for offshore earthquakes were well constrained teleseismic cmt also provides robust solutions but our regional 3d cmt could provide better constraints of dip angles our 3d cmt catalogue and published slow earthquake catalogues depicted spatial distributions of slip behaviours on the plate boundary along the nankai trough the regular and slow interplate earthquakes were separately distributed with these distributions reflecting the heterogeneous distribution of effective strengths along the nankai trough plate boundary by comparing the spatial distribution of seismic slip on the plate boundary with the slip deficit rate distribution regions with strong coupling were clearly identified

spatial distribution of seismic energy rate of tectonic tremors in subduction zones the sizes of deep tectonic tremors have never been accurately evaluated as a physical quantity here we estimate tremor size as the band limited seismic energy rate at 2 8 hz with accurate evaluation of the path attenuation and site amplification of seismic waves in four subduction zones nankai cascadia jalisco and south chile the size frequency statistics of seismic energy rate which are characterized by the median measure for each subregion are spatially variable the spatial variations are categorized into three types with each type corresponding to a different tremor migration behavior in type a regions where tremor zone is wider seismic energy rates are highly variable in the dip direction and tremor activities are usually initiated in the less energetic tremor zone some of them further penetrate into the energetic tremor zone and subsequently migrate for long distances in the strike direction type b regions are characterized by relatively narrow tremor zones minor variations in energy rates in the dip direction and long distance migration in the strike direction type c regions are characterized by isolated clusters of tremor activities without migration and by independent failure of each small tremor cluster given that the spatial distributions of tremor energy rates reflect heterogeneities in the strength of the plate interface such distributions which would be controlled by the width of tremor zone may determine the regional style of slow earthquake behavior some energetic tremor regions act as switches that trigger large slow slip events especially in type a regions

an early eocene carbon cycle perturbation at 52 5 ma in the southern alps chronology and biotic response an early eocene carbon cycle perturbation at 52 5 ma from the southern alps chronology and biotic response

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