back arc opening in the western end of the okinawa trough revealed from gnss acoustic measurements we measured seafloor movement using a global navigation satellite systems gnss acoustic technique at the south of the rifting valley in the western end of the okinawa trough back arc basin 60 km east of northeastern corner of taiwan the horizontal position of the seafloor benchmark measured eight times between july 2012 and may 2016 showed a southeastward movement suggesting a back arc opening of the okinawa trough the average velocity of the seafloor benchmark shows a block motion together with yonaguni island the westernmost part of the ryukyu arc rotates clockwise and is pulled apart from the taiwan island which should cause the expansion of the yilan plain taiwan comparing the motion of the seafloor benchmark with adjacent seismicity we suggest a gentle episodic opening of the rifting valley accompanying a moderate seismic activation which differs from the case in the segment north off yonaguni island where a rapid dyke intrusion occurs with a significant seismic activity

three dimensional splay fault geometry and implications for tsunami generation megasplay faults very long thrust faults that rise from the subduction plate boundary megathrust and intersect the sea floor at the landward edge of the accretionary prism are thought to play a role in tsunami genesis we imaged a megasplay thrust system along the nankai trough in three dimensions which allowed us to map the splay fault geometry and its lateral continuity the megasplay is continuous from the main plate interface fault upwards to the sea floor where it cuts older thrust slices of the frontal accretionary prism the thrust geometry and evidence of large scale slumping of surficial sediments show that the fault is active and that the activity has evolved toward the landward direction with time contrary to the usual seaward progression of accretionary thrusts the megasplay fault has progressively steepened substantially increasing the potential for vertical uplift of the sea floor with slip we conclude that slip on the megasplay fault most likely contributed to generating devastating historic tsunamis such as the 1944 moment magnitude 8 1 tonankai event and it is this geometry that makes this margin and others like it particularly prone to tsunami genesis

paleotsunami research along the nankai trough and ryukyu trench subduction zones current achievements and future challenges abstract located near japan s most densely populated and industrially active region the nankai trough subduction zone has long been highlighted as a high risk area for damaging earthquakes and tsunamis in contrast less attention has been paid the adjacent ryukyu trench because historical and geological records are scarce in order to develop better quantitative estimates of the timing and size of the earthquakes and tsunamis generated along these subduction zones comprehensive studies using geological seismological and historical methods have been conducted since the 1990s studies of tsunami deposits in this region have contributed to our current understanding of the history of tsunamis over the last 6000 years following the 2011 t hoku earthquake and tsunami paleotsunami research has especially focused on guiding and enhancing tsunami disaster management and mitigation measures the last nine years have seen a rapid increase in paleotsunami data from the nankai trough and ryukyu trench coasts these recent studies reveal that there are significant differences in the size and recurrence pattern of earthquakes and tsunamis along these subduction zones for instance large earthquakes have repeatedly occurred along the nankai trough every 100 200 years on the other hand large earthquakes and tsunamis may not have occurred over the last few thousand years at the junction between these subduction zones there is also no evidence for the occurrence of large earthquakes along the northern and central ryukyu trench over this time period large earthquakes and tsunamis may have occurred every few hundred years at the southern end of the ryukyu trench nevertheless data on the occurrence of these earthquakes are still insufficient both in quantity and quality to estimate the maximum size or recurrence pattern

spatiotemporal distribution of interplate coupling in southwest japan from inversion of geodetic data 1 we determine the spatiotemporal distribution of slip or slip deficit on the subduction interface of the nankai trough over an entire earthquake cycle using geodetic data including leveling triangulation and trilateration sea level and gps surveys obtained during the past 100 years in southwest japan we develop a new inversion method that accounts for long term crustal deformation coseismic earthquake displacements and stress relaxation of the viscoelastic asthenosphere from this analysis we obtain a model that shows postseismic afterslip on the deeper part of the plate interface following the 1946 nankaido earthquake significant afterslip is found beneath central shikoku that totals about 0 8 m the slip deficit rate during the interseismic period is 5 6 cm year in the n50 w n60 w direction which is consistent with the relative plate motion between the philippine and amurian plates a fully locked region is found in the shallower portion 30 km and the slip deficit rate has a maximum at a depth of about 20 km the plate interface deeper than 30 km is slowly slipping the amount of slip deficit reaches about 3 3 m off shikoku and about 2 m off the kii peninsula 50 years after the 1946 earthquake this suggests that fault healing and full interplate coupling has occurred by this time along the nankai trough

predicting imminence of analog megathrust earthquakes with machine learning implications for monitoring subduction zones abstract subduction zones are monitored using space geodesy with increasing resolution with the aim of better capturing the deformation accompanying the seismic cycle here we investigate data characteristics that maximize the performance of a machine learning binary classifier predicting slip event imminence we overcome the scarcity of recorded instances from real subduction zones using data from a seismotectonic analog model monitored with a spatially dense continuously recording onshore geodetic network we show that a 70 85 km wide coastal swath recording interseismic deformation gives the most important information on slip imminence prediction performances are mainly influenced by the alarm duration amount of time that we consider an event as imminent with density of stations and record length playing a secondary role the techniques developed in this study are most likely applicable in regions of slow earthquakes where stick slip like failures occur at time intervals of months to years

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

precise gps acoustic positioning of seafloor reference points for tectonic studies abstract global networks for crustal strain measurement provide important constraints for studies of tectonic plate motion and deformation to date crustal strain measurements have been possible only in terrestrial settings on continental plates and island sites within oceanic plates we report the development of technology for horizontal crustal motion determination at seafloor sites allowing oceanic plates to be monitored where islands are not available seafloor crustal monitoring is an important component of global strain measurement because about 70 of the earth s surface is covered by water and this region contains most of the tectonic plate boundaries and zones of crustal deformation using the global positioning system gps satellites and underwater acoustics we have established a geodetic reference site on the juan de fuca plate at 2 6 km depth approximately 150 km off the northwest coast of north america we measure the baselines between this site and two terrestrial gps stations on vancouver island british columbia the juan de fuca plate site is an appropriate setting to develop seafloor observation methods since it is a well studied area easily accessible from west coast canadian and united states ports determination of seafloor motion at this site addresses questions related to convergence between the juan de fuca and north american plates across the cascadia subduction zone at the juan de fuca seafloor geodetic reference site we installed precision acoustic transponders on the seafloor and measured ranges to them from a sound source at a surface platform ship or buoy the platform is equipped with a set of three gps antennas allowing determination of the sound source position at times of signal transmission and reception merging the satellite and acoustic data allows determination of the transponder network location in global reference frame coordinates data processing to date suggests repeatabilities of 0 8 cm north and 3 9 cm east in the seafloor transponder network position relative to reference points on vancouver island

evidence of viscoelastic deformation following the 2011 tohoku oki earthquake revealed from seafloor geodetic observation the gps acoustic seafloor positioning has detected significant postseismic movements after the 2011 tohoku oki earthquake m9 0 just above the source region off the pacific coast of eastern japan in contrast to the coastal global navigation satellite systems sites where trenchward upward movements were reported the offshore sites above the main rupture zone in the northern part of the source region exhibit landward displacements of tens of centimeters with significant subsidence from almost 3 years of repeated observations at the sites above around the edge of the main rupture zone smaller amount of trench normal movements was found although the terrestrial movements were reasonably interpreted by afterslip beneath the coastal area these offshore results are rather consistent with effects predicted from viscoelastic relaxation in the upper mantle providing definitive evidence of its occurrence on the other hand the results in the southern part of the source region imply superposition of effects from viscoelastic relaxation and afterslip

introduction of covariance components in slip inversion of geodetic data following a non uniform spatial distribution and application to slip deficit rate estimation in the nankai trough subduction zone when spatial distribution of observation stations has bias in geodetic slip inversion modeling errors in the inversion scheme may result in significant unnatural short wave components in estimated slip distribution which overfit to data combined use of both land and seafloor geodetic data in slip inversion often leads to such situations to avoid overfitting i proposed a method to incorporate proper covariance components in the data covariance matrix originated by modeling errors in the geodetic slip inversion because linearity of the inversion problem is retained widely known approaches to introduce prior constraints to the inversion which assumes linear inversion are easily applied to the proposed method synthetic tests showed that the introduction of covariance components allowed for the estimation of slip distributions closer to the true one avoiding overfitting to geodetic data in biasedly distributed observation stations compared to a conventional approach that does not introduce covariance components i applied the proposed method to the estimation of the slip deficit rate in the nankai trough subduction zone using geodetic data of displacement rates provided by land gnss stations and seafloor gnss acoustic stations the proposed method estimated a reasonably smooth distribution of slip deficit rate compared to the conventional approach spatial distribution of residuals in the displacement rates suggested that the proposed method successfully avoids overfitting to the block motion at the south of the median tectonic line which the physical model i assumed here cannot describe

migration of shallow and deep slow earthquakes toward the locked segment of the nankai megathrust abstract the nankai megathrust is located offshore shikoku and kyushu japan and is characterized by various kinds of slow earthquakes whose relative motions across the plate boundary faults are slower than regular earthquakes in the area the interplate locking is stronger in the northern area offshore shikoku than in the southern area offshore kyushu and mw 8 earthquakes nankai earthquakes have occurred repeatedly in the northern area in this paper the spatio temporal distributions of slow earthquakes very low frequency earthquakes tremors and slow slip events are examined based on the analyses of repeating earthquakes and slow earthquakes with special focus on the interaction between different activities a comprehensive analysis of the seismic and geodetic data from 2003 to 2016 indicates complementary distribution of various types of slow earthquakes down to 35 50 km depth outside the nankai main locking area we also found interactions between different kinds of activities the interactions between the repeating earthquakes and slow earthquakes suggest that the area of the repeating earthquakes activity can be divided into deeper depth 20 km and shallower depth

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

suboceanic geodetic measurements this paper reviews the needs for geodetic ties among seafloor points and between such points and others on land as well as the environmental constraints on potential systems for making such measurements underwater acoustic techniques provide the best opportunities and an essential element on which to build acoustic systems a precision transponder system capable of making travel time measurements over ranges of several kilometers with an accuracy of a few microseconds is described finally three particular systems are discussed one uses direct transmission between transponders to achieve one part in 105 accuracy over ranges from a few meters to about a kilometer the second using a larger transponder network and an intermediate vehicle can achieve similar accuracy over ranges up to about 10 km the third is a composite acoustic global positioning system gps which should be able to achieve subdecimeter accuracy over ranges of a few hundred kilometers

imaging of the subducted kyushu palau ridge in the hyuga nada region western nankai trough subduction zone abstract we performed 3d seismic tomography of the hyuga nada region western nankai subduction zone to investigate the relationship of the subducted part of kyushu palau ridge kpr to coseismic rupture propagation seismicity and shallow very low frequency earthquakes combining active source and passive source data recorded both onshore and offshore we imaged the deep slab from near the trough axis to the coastal area our results show the subducted kpr as a low velocity belt oriented nw se extending down the plate boundary to around 30 km depth at this depth we suggest that the subducted kpr detaches from the slab and becomes underplated on the overriding continental plate as the coseismic slip areas of past large earthquakes do not extend into the subducted kpr we suggest that it may inhibit rupture propagation the interior of the subducted kpr shows active intraslab seismicity with a wide depth distribution shallow very low frequency earthquakes are continuously active above the location of the subducted kpr whereas they are intermittent to the northeast of the subducted kpr thus the subducted kpr appears to be an important factor in coseismic rupture propagation and seismic phenomena in this region

influence of enhanced abyssal diapycnal mixing on stratification and the ocean overturning circulation abstractthe meridional overturning circulation moc is composed of interconnected overturning cells that transport cold dense abyssal waters formed at high latitudes back to the surface turbulent diapycnal mixing plays a primary role in setting the rate and patterns of the various overturning cells that constitute the moc the focus of the analyses in this paper will be on the influence of sharp vertical variations in mixing on the moc and ocean stratification mixing is enhanced close to the ocean bottom topography where internal waves generated by the interaction of tides and geostrophic motions with topography break it is shown that the sharp vertical variations in mixing lead to the formation of three layers with different dynamical balances governing meridional flow specifically an abyssal bottom boundary layer forms above the ocean floor where mixing is largest and hosts the northward transport of the heaviest waters from the southern channel to the closed basins a deep layer forms above the b

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

subducted seamount imaged in the rupture zone of the 1946 nankaido earthquake the nankai trough is a vigorous subduction zone where large earthquakes have been recorded since the seventh century with a recurrence time of 100 to 200 years the 1946 nankaido earthquake was unusual with a rupture zone estimated from long period geodetic data that was more than twice as large as that derived from shorter period seismic data in the center of this earthquake rupture zone we used densely deployed ocean bottom seismographs to detect a subducted seamount 13 kilometers thick by 50 kilometers wide at a depth of 10 kilometers we propose that this seamount might work as a barrier inhibiting brittle seismogenic rupture

dynamic rupture scenarios of anticipated nankai tonankai earthquakes southwest japan 1 we investigated dynamic rupture scenarios of anticipated megathrust earthquakes on the nankai tonankai subduction zone southwest japan to improve the scenario reliability the model parameters should be constrained by available data or derived from their analysis we employed the three dimensional plate interface geometry and the slip deficit rate on the interface accumulated slip deficit was used to obtain the stress drop distribution of anticipated earthquakes the estimated stress drop distribution is consistent with the seismogenic asperity locations known from the analysis of past earthquakes fault friction constitutive parameters however had to be assumed from indirect observations because they cannot be constrained directly by the data based on various geophysical observations we defined three regions where larger fracture energy is required these are the eastern edge of the tonankai area the western edge of the nankai area and the region between the tonankai and nankai areas beneath the kii peninsula such lateral heterogeneity promoted the segmented rupture along the nankai trough with predefined stress drop and constitutive parameters various rupture scenarios for tonankai and nankai asperities were obtained for different initiation locations in some cases a single segment is ruptured while in other cases all the segments are broken due to dynamic linkage at the segment boundary causing a giant earthquake the initiation location is a critical parameter that controls the rupture propagation across the segment boundary these scenarios will be extremely useful to evaluate deterministically the strong ground motions and tsunami hazards caused by the next major earthquakes in southwest japan

roughness characteristics of oceanic seafloor prior to subduction in relation to the seismogenic potential of subduction zones we have developed a new approach to characterize the seafloor roughness seaward of the trenches as a proxy for estimating the roughness of the subduction interface we consider that abrupt elevation changes over given wavelengths play a larger role in the seismogenic behavior of the subduction interface than the amplitude of bathymetric variations alone the new database subrough provides roughness parameters at selected spatial wavelengths here we mainly discuss the spatial distribution of short 12 20 km and long wavelength 80 100 km roughness rsw and rlw respectively along 250 km wide strips of seafloor seaward of the trenches compared with global trend seamounts show distinct roughness signature of much larger amplitudes at both wavelengths whereas aseismic ridges only differ from the global trend at long wavelengths fracture zones cannot be distinguished from the global trend which suggests that their potential effect on rupture dynamics is not the consequence of their roughness at least not at these wavelengths based on rlw amplitude segments along subduction zones can be defined from rough to smooth subduction zones like the solomons or the ryukyus appear dominantly rough whereas others like the andes or cascadia are dominantly smooth the relative contribution of smooth versus rough areas in terms of respective lateral extents probably plays a role in multipatch rupture and thus in the final earthquake magnitude we observe a clear correlation between high seismic coupling and relatively low roughness and conversely between low seismic coupling and relatively high seafloor roughness

wedge geometry frictional properties and interseismic coupling of the java megathrust abstract the mechanical interaction between rocks at fault zones is a key element for understanding how earthquakes nucleate and propagate therefore estimating frictional properties along fault planes allows us to infer the degree of elastic strain accumulation throughout the seismic cycle the java subduction zone is an active plate boundary where high seismic activity has long been documented however very little is known about the seismogenic processes of the megathrust especially its shallowest portion where onshore geodetic networks are insensitive to recover the pattern of elastic strain here we use the geometry of the offshore accretionary prism to infer frictional properties along the java subduction zone using coulomb critical taper theory we show that large portions of the inner wedge in the eastern part of the java subduction megathrust are in a critical state where the wedge is on the verge of failure everywhere we identify four clusters with an internal coefficient of friction int of 0 8 and hydrostatic pore pressure within the wedge the average effective coefficient of friction ranges between 0 3 and 0 4 reflecting a strong decollement our results also show that the aftershock sequence of the 1994 mw 7 9 earthquake halted adjacent to a critical segment of the wedge suggesting that critical taper wedge areas in the eastern java subduction interface may behave as a permanent barrier to large earthquake rupture in contrast in western java topographic slope and slab dip profiles suggest that the wedge is mechanically stable i e deformation is restricted to sliding along the decollement and likely to coincide with a seismogenic portion of the megathrust we discuss the seismic hazard implications and highlight the importance of considering the segmentation of the java subduction zone when assessing the seismic hazard of this region

interseismic seafloor crustal deformation immediately above the source region of anticipated megathrust earthquake along the nankai trough japan 1 we monitored seafloor crustal deformation using the gps acoustic seafloor geodetic observation technique at three sites on the kumano basin off southwestern japan which is located immediately above the source region of the anticipated tonankai megathrust earthquake we directly measured landward crustal movements of 40 mm y in the n80 w direction with respect to the amurian plate on the seafloor the directions were found to be the same as those measured at the on land gps stations the magnitudes of the velocity vectors indicated significant crustal shortenings of approximately 10 20 mm y between the kumano basin and the southeastern coast of the kii peninsula of the japanese islands the present observational results show strong and direct evidence for interplate locking during the interseismic period coupling ratios were roughly estimated at 0 6 0 8 on the plate interface up to at least 10 km in depth

a comprehensive analysis of the illapel 2015 mw8 3 earthquake from gps and insar data the september 16 2015 mw8 3 illapel earthquake occurred on a locked segment of the south american subduction in chile this segment ruptured during comparable size earthquakes in the past in 1880 and 1943 suggesting a somehow regular pattern of characteristic mw 8 earthquakes occurring every 60 to 80 years this recurrence is in agreement with the accumulation of elastic deformation in the upper plate due to the nazca south america subduction at a constant rate of 6 5 cm year leading to a deficit of 4 5 meters of slip to be released every 70 years previous studies consistently imaged the distribution of co seismic slip along the fault based on geodetic seismological and far field tsunami data and all described a significant amount of shallow slip resulting in a large tsunami in addition some models highlighted an apparent mismatch between the modeled rake of slip and the direction of plate convergence suggesting the buildup of large strike slip deficit some of these important questions remain open is shallow slip really well resolved and substantiated is the apparent principal direction of slip during the earthquake really required by the geodetic data here using a comprehensive analysis of continuous gps sites including high rate and static displacements and new survey data from acquired over more than 50 pre existing sites complemented with insar data we show that the 2015 rupture overlaps very well the 1943 rupture with the absence of significant slip south of 32 s and north of 30 2 s peninsula lingua de vaca despite the wealth of geodetic data the shallowest part of the subduction interface remains poorly resolved we also show that the rake of the earthquake is fully compatible with the oblique plate convergence direction rather than perpendicular to the trench meaning that no subsequent trench parallel motion is required by the data we propose that the large low coupling zone lcz at the latitude of la serena revealed by present day coupling distribution is stable over at least two seismic cycles inside the coupled area peak coseismic slip is located precisely offshore the highest coastal topography and elevated terraces adding weight to a potential correlation between the seismic cycle and long term permanent deformation finally we show that early post seismic after slip occurs mostly down dip of co seismic asperity ies extending north and south of the 2015 rupture area

heterogeneous coupling of the sumatran megathrust constrained by geodetic and paleogeodetic measurements geodetic and paleogeodetic measurements of interseismic strain above the sumatran portion of the sunda subduction zone reveal a heterogeneous pattern of coupling annual banding in corals provides vertical rates of deformation spanning the last half of the 20th century and repeated gps surveys between 1991 and 2001 and continuous measurements at gps stations operated since 2002 provide horizontal velocities near the equator the megathrust is locked over a narrow width of only a few tens of kilometers in contrast the locked fault zone is up to about 175 km wide in areas where great interplate earthquakes have occurred in the past formal inversion of the data reveals that these strongly coupled patches are roughly coincident with asperities that ruptured during these events the correlation is most spectacular for rupture of the m w 8 7 nias simeulue earthquake of 2005 which released half of the moment deficit that had accumulated since its previous rupture in 1861 suggesting that this earthquake was overdue beneath the mentawai islands strong coupling is observed within the overlapping rupture areas of the great earthquakes of 1797 and 1833 the accumulated slip deficit since these events is slowly reaching the amount of slip that occurred during the 1833 earthquake but already exceeds the slip that occurred during the 1797 earthquake thus rerupture of part of the mentawai patch in september 2007 was not a surprise in contrast coupling is low below the batu islands near the equator and around enggano island at about 5 s where only moderate earthquakes m w 8 0 have occurred in the past two centuries the correlation of large seismic asperities with patches that are locked during the interseismic period suggests that they are persistent features this interpretation is reinforced by the fact that the large locked patches and great ruptures occur beneath persistent geomorphologic features the largest outer arc islands depth and convergence rate dependent temperature might influence the pattern of coupling through its effect on the rheology of the plate interface but other influences are required to account for the observed along strike heterogeneity of coupling in particular subduction of the investigator fracture zone could be the cause for the low coupling near the equator

3 d modelling of plate interfaces and numerical simulation of long term crustal deformation in and around japan we developed a 3 d simulation model for long term crustal deformation due to steady plate subduction in and around japan by incorporating viscoelastic slip response functions into a realistic 3 d plate interface model constructed on the basis of the topography of ocean floors and hypocenter distributions of earthquakes the lithosphere asthenosphere system is modelled by an elastic surface layer overlying a maxwellian viscoelastic half space kinematic interaction at plate interfaces is rationally represented by the increase of tangential displacement discontinuity fault slip across the interfaces with this model giving the steady slip rates at plate interfaces calculated from nuvel 1a we simulated long term crustal deformation due to steady plate subduction in and around japan the simulated crustal deformation pattern is characterized by steep uplift at island arcs sharp subsidence at ocean trenches and gentle uplift at outer rises the numerical results show the strong dependence of the deformation pattern on the 3 d geometry of plate interfaces

modeling of long period ground motions in the nankai subduction zone model simulation using the accretionary prism derived from oceanfloor local s wave velocity structures the accretionary prism in the subduction zone which consists of thick low velocity oceanic sediments significantly affects the propagation of seismic waves for shallow offshore earthquakes including large interplate earthquakes in order to simulate long period 5 s ground motions in the nankai subduction zone we constructed a three dimensional 3d seismic velocity structure model of the accretionary prism by interpolation extrapolation of local s wave velocity structures beneath 46 oceanfloor seismic stations donet which are deployed just above the accretionary prism off the southern kii and eastern shikoku regions we modeled local s wave velocity structures using a simple two parameter depth varying velocity function to investigate the effects of the accretionary prism on ground and seafloor motions we conducted numerical simulations of seismic wave propagation for three local earthquakes that occurred in southwestern japan the simulations reasonably reproduced the observed seismograms not only for the period ranges of the moment tensor inversion 50 s but also for the strong long period ground motions in the sedimentary basins 5 s especially in the region where donet stations are densely deployed since depth varying local s wave structures significantly improve the reproducibility of long period ground motions our modeling procedure is useful for modeling long period ground motions of local and regional offshore subduction zone earthquakes

slow earthquakes linked along dip in the nankai subduction zone we identified a strong temporal correlation between three distinct types of slow earthquakes distributed over 100 kilometers along the dip of the subducting oceanic plate at the western margin of the nankai megathrust rupture zone southwest japan in 2003 and 2010 shallow very low frequency earthquakes near the nankai trough as well as nonvolcanic tremor at depths of 30 to 40 kilometers were triggered by the acceleration of a long term slow slip event in between this correlation suggests that the slow slip might extend along dip between the source areas of deeper and shallower slow earthquakes and thus could modulate the stress buildup on the adjacent megathrust rupture zone

measuring the onset of locking in the peru chile trench with gps and acoustic measurements the subduction zone off the west coast of south america marks the convergence of the oceanic nazca plate and the continental south america plate nazca south america convergence over the past 23 million years has created the 6 km deep peru chile trench 150 km offshore high pressure between the plates creates a locked zone leading to deformation of the overriding plate the surface area of this locked zone is thought to control the magnitude of co seismic release and is limited by pressure temperature sediment type and fluid content1 here we present seafloor deformation data from the submerged south america plate obtained from a combination of global positioning system gps receivers and acoustic transponders we estimate that the measured horizontal surface motion perpendicular to the trench is consistent with a model having no slip along the thrust fault between 2 and 40 km depth a tsunami in 1996 200 km north of our site was interpreted as being the result of an anomalously shallow interplate earthquake2 seismic coupling at shallow depths such as we observe may explain why co seismic events in the peruvian subduction zone create large tsunamis

tsunami scenarios based on interseismic models along the nankai trough japan from seafloor and onshore geodesy the recent availability of global positioning system acoustic seafloor geodetic observations enables us to resolve the spatial distribution of the slip deficit rate near the nankai trough southwestern japan considering a tectonic block model and the transient deformation due to the major earthquakes in this area the slip deficit rate between the two relevant blocks can be estimated in this study we remove the time dependent postseismic deformation of the 2004 southeastern off the kii peninsula earthquakes mjma 7 1 7 4 which had led to the underestimation of the slip deficit rate in earlier studies we model the postearthquake viscoelastic relaxation using the 3d finite element model with bi viscous burgers rheology as well as the afterslip on the finite faults the corrected global positioning system acoustic and land based global navigation satellite systems data are aligned to the existing tectonic model and used to estimate the slip deficit rate on the plate boundary we then calculate the coseismic displacements and tsunami wave propagation with the simple assumption that a hundred years of constant slip deficit accumulation was released instantaneously to evaluate the influence of uncertainties in the plate interface geometry on a tsunami model for the nankai trough we investigated two different geometries and performed checkerboard inversion simulations although the two models indicate roughly similar results the peak height of the tsunami wave and its arrival time at several points are significantly different in terms of the expected hazard

itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters 1 unlike the past international terrestrial reference frame itrf versions where global long term solutions were combined the itrf2005 uses as input data time series weekly from satellite techniques and 24 h session wise from very long baseline interferometry of station positions and daily earth orientation parameters eops the advantage of using time series of station positions is that it allows to monitor station non linear motion and discontinuities and to examine the temporal behavior of the frame physical parameters namely the origin and the scale the itrf2005 origin is defined in such a way that it has zero translations and translation rates with respect to the earth center of mass averaged by the satellite laser ranging slr time series spanning 13 years of observations its scale is defined by nullifying the scale and its rate with respect to the very long baseline interferometry vlbi time series spanning 26 years of observations the itrf2005 orientation at epoch 2000 0 and its rate are aligned to the itrf2000 using 70 stations of high geodetic quality the estimated level of consistency of the itrf2005 origin at epoch 2000 0 and its rate with respect to the itrf2000 is respectively 0 1 0 8 5 8 mm and 0 2 0 1 1 8 mm yr along the x yand z axis we estimate the formal errors on these components to be 0 3 mm and 0 3 mm yr we believe that this low level of agreement between the two frame origins is most probably due to the poor slr network geometry and its degradation over time the itrf2005 combination involving 84 co location sites revealed a scale inconsistency of 1 ppb 6 3 mm at the equator at epoch 2000 0 and 0 08 ppb yr between the slr and vlbi long term solutions as obtained by the stacking of their respective time series possible causes of this inconsistency may include the poor slr and vlbi networks and their co locations local tie uncertainties systematic effects and possible inconsistent model corrections used in the data analysis of both techniques for the first time of the itrf history the itrf2005 rigorous combination provides self consistent series of eops including polar motion from vlbi and satellite techniques and universal time and length of day from vlbi only a velocity field of 152 sites with an error less than 1 5 mm yr is used to estimate absolute rotation poles of 15 tectonic plates that are consistent with the itrf2005 frame this new absolute plate motion model supersedes and significantly improves that of the itrf2000 which involved six major tectonic plates citation altamimi z x collilieux j legrand b garayt and c boucher 2007 itrf2005 a new release of the international terrestrial reference frame based on time series of station positions and earth orientation parameters j geophys res 112 b09401

2010 maule earthquake slip correlates with pre seismic locking of andean subduction zone analysis of seismic data and global positioning system gps observations from the region around the site of the recent magnitude 8 8 maule earthquake in chile have been combined with modelling of the andean subduction zone to build up a detailed image of the event the earthquake occurred at a seismic gap part of the fault that has not experienced a major earthquake since 1835 and it seems to have released most of the stress accumulated since that time the observations suggest that coseismic slip heterogeneity at the scale of single asperities and therefore the seismic potential of future great earthquakes might be anticipated by geodetic observations these authors show evidence for a high coherence between the slip distribution inferred from the 2010 maule earthquake chile and the patchwork of interseismic locking distribution derived from global positioning system observations during the previous decade their work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future earthquakes which thus might be anticipated by geodetic observations the magnitude 8 8 maule chile earthquake of 27 february 2010 ruptured a segment of the andean subduction zone megathrust that has been suspected to be of high seismic potential1 2 3 4 5 6 it is the largest earthquake to rupture a mature seismic gap in a subduction zone that has been monitored with a dense space geodetic network before the event this provides an image of the pre seismically locked state of the plate interface of unprecedentedly high resolution allowing for an assessment of the spatial correlation of interseismic locking with coseismic slip pre seismic locking might be used to anticipate future ruptures in many seismic gaps6 7 8 9 10 11 12 given the fundamental assumption that locking and slip are similar this hypothesis however could not be tested without the occurrence of the first gap filling earthquake here we show evidence that the 2010 maule earthquake slip distribution correlates closely with the patchwork of interseismic locking distribution as derived by inversion of global positioning system gps observations during the previous decade the earthquake nucleated in a region of high locking gradient and released most of the stresses accumulated in the area since the last major event in 1835 two regions of high seismic slip asperities appeared to be nearly fully locked before the earthquake between these asperities the rupture bridged a zone that was creeping interseismically with consistently low coseismic slip the rupture stopped in areas that were highly locked before the earthquake but where pre stress had been significantly reduced by overlapping twentieth century earthquakes our work suggests that coseismic slip heterogeneity at the scale of single asperities should indicate the seismic potential of future great earthquakes which thus might be anticipated by geodetic observations

creeping subduction zones are weaker than locked subduction zones faults that are fully or partially locked pose the greatest seismic hazard because they accumulate stress that can then be released in large earthquakes in contrast other faults continuously creep the creeping versus locked behaviour is probably related to the frictional properties of the fault and the effective normal stress on the fault but it is unclear whether locked faults are weaker or stronger than creeping faults here we use stress orientations in subduction zones from inversion of earthquake moment tensors and find that geodetically determined creeping versus locked behaviour is correlated with the orientation of the subduction zone plate boundary fault relative to the principal stress axes globally locked subduction zones appear well oriented for failure assuming a typical laboratory friction coefficient creeping subduction zones are more poorly oriented implying a lower apparent friction coefficient due to either low intrinsic friction or reduced effective normal stress the spatial variations of stress orientation on the japan trench are similarly correlated with spatial variations in coupling with creeping regions having a lower apparent friction coefficient than locked regions the absolute strength of faults is influenced by the ambient fluid pressure which is often elevated in subduction zones this suggests low overall strength for locked subduction zone faults and additional strength reduction in creeping zones that may be due to transient elevated fluid pressures the faults in creeping segments of subduction zones are weaker than those in locked segments according to analyses of stress orientations and gps data from subduction zones globally

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

splay fault branching along the nankai subduction zone seismic reflection profiles reveal steeply landward dipping splay faults in the rupture area of the magnitude m 8 1 tonankai earthquake in the nankai subduction zone these splay faults branch upward from the plate boundary interface that is the subduction zone at a depth of approximately 10 kilometers approximately 50 to 55 kilometers landward of the trough axis breaking through the upper crustal plate slip on the active splay fault may be an important mechanism that accommodates the elastic strain caused by relative plate motion

spatial and temporal distributions of b values related to long term slow slip and low frequency earthquakes in the bungo channel and hyuga nada regions japan abstract long term slow slip events sses and low frequency earthquakes lfes repeatedly occur in the area encompassing the bungo channel and hyuga nada region in japan sses are slow earthquake events with a duration of months to years characterized by a type of slip that is considered transitional between the fast rupture of regular earthquakes and stable sliding along a plate interface and have characteristics sensitive to stress states near the plate interface in addition since lfes are also thought to occur at the plate interface it would be useful to infer the stress state in this region this study focuses on the stress dependent characteristics of the b values of regular earthquakes sses and lfes as well as the spatio temporal relationships between b values and these events in this area using the japan unified high resolution relocated catalog for earthquakes juice the b value which represents the relative proportion of large to small earthquakes is inversely related to differential stress or effective stress the b values are moderate to low b 0 6 1 1 in regions with a high incidence of long term sses this spatial b value anomaly is attributed to the partial release of accumulated stress in regions with a relatively high differential stress due to sse activity furthermore the b value distributions estimated in this study provide constraints on the mechanisms that generate lfes on the other hand the b values increase and decrease before and during periods of enhanced lfe activity in the bungo channel respectively the increase and following decrease in b values are thought to reflect episodes of low and high shear strength along the plate interface which were caused by the presence of abundant slab derived fluids under undrained conditions above the plate interface and decreased pore pressure related to fluid depletion via lfe generation respectively

deformation cycles of subduction earthquakes in a viscoelastic earth subduction zones produce the largest earthquakes over the past two decades space geodesy has revolutionized our view of crustal deformation between consecutive earthquakes the short time span of modern measurements necessitates comparative studies of subduction zones that are at different stages of the deformation cycle piecing together geodetic snapshots from different subduction zones leads to a unifying picture in which the deformation is controlled by both the short term years and long term decades and centuries viscous behaviour of the mantle traditional views based on elastic models such as coseismic deformation being a mirror image of interseismic deformation are being thoroughly revised snapshots of subduction zones using space geodesy reveal that the viscous behaviour of the mantle controls crustal deformation requiring the revision of traditional elastic models for earthquake risk assessment space geodesy the use of satellites to monitor earth has revolutionized our view of crustal deformation between consecutive earthquakes however the brevity of such measurements means that studies must be done by comparing multiple subduction zones at different stages of the earthquake cycle by piecing together geodetic snapshots from the sumatra chile and cascadia subduction zones this review presents a unifying picture in which deformation is controlled by the viscous behaviour of the mantle in both the short term years and the long term decades to centuries

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

near field observations of an offshore mw 6 0 earthquake from an integrated seafloor and subseafloor monitoring network at the nankai trough southwest japan an mw 6 0 earthquake struck 50 km offshore the kii peninsula of southwest honshu japan on 1 april 2016 this earthquake occurred directly beneath a cabled offshore monitoring network at the nankai trough subduction zone and within 25 35 km of two borehole observatories installed as part of the international ocean discovery program s nantroseize project the earthquake s location close to the seafloor and subseafloor network offers a unique opportunity to evaluate dense seafloor geodetic and seismological data in the near field of a moderate sized offshore earthquake we use the offshore seismic network to locate the main shock and aftershocks seafloor pressure sensors and borehole observatory data to determine the detailed distribution of seafloor and subseafloor deformation and seafloor pressure observations to model the resulting tsunami contractional strain estimated from formation pore pressure records in the borehole observatories equivalent to 0 37 to 0 15 strain provides a key to narrowing the possible range of fault plane solutions together these data show that the rupture occurred on a landward dipping thrust fault at 9 10 km below the seafloor most likely on the plate interface pore pressure changes recorded in one of the observatories also provide evidence for significant afterslip for at least a few days following the main shock the earthquake and its aftershocks are located within the coseismic slip region of the 1944 tonankai earthquake mw 8 0 and immediately downdip of swarms of very low frequency earthquakes in this region illustrating the complex distribution of megathrust slip behavior at a dominantly locked seismogenic zone

seismic and aseismic slip on the central peru megathrust slip on a subduction megathrust can be seismic or aseismic with the two modes of slip complementing each other in time and space to accommodate the long term plate motions although slip is almost purely aseismic at depths greater than about 40 km heterogeneous surface strain suggests that both modes of slip occur at shallower depths with aseismic slip resulting from steady or transient creep in the interseismic and postseismic periods thus active faults seem to comprise areas that slip mostly during earthquakes and areas that mostly slip aseismically the size location and frequency of earthquakes that a megathrust can generate thus depend on where and when aseismic creep is taking place and what fraction of the long term slip rate it accounts for here we address this issue by focusing on the central peru megathrust we show that the pisco earthquake with moment magnitude m w 8 0 ruptured two asperities within a patch that had remained locked in the interseismic period and triggered aseismic frictional afterslip on two adjacent patches the most prominent patch of afterslip coincides with the subducting nazca ridge an area also characterized by low interseismic coupling which seems to have repeatedly acted as a barrier to seismic rupture propagation in the past the seismogenic portion of the megathrust thus appears to be composed of interfingering rate weakening and rate strengthening patches the rate strengthening patches contribute to a high proportion of aseismic slip and determine the extent and frequency of large interplate earthquakes aseismic slip accounts for as much as 50 70 of the slip budget on the seismogenic portion of the megathrust in central peru and the return period of earthquakes with m w 8 0 in the pisco area is estimated to be 250 years

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

seafloor geodetic constraints on interplate coupling of the nankai trough megathrust zone seafloor geodetic data from the nankai trough off southwestern japan show that most offshore sites in this earthquake prone region have high slip deficit rates revealing previously unknown locations that could be important for the mitigation of future earthquake and tsunami associated disasters yusuke yokota et al have used seafloor geodetic observations to visualize the seismogenic zone along the nankai trough off southwestern japan which is thought to be one of the most dangerous megathrust zones in the world they suggest that most offshore sites in this region have positive slip deficit rates revealing previously unknown locations that could be potential sources of future earthquakes and tsunamis low slip deficit rates are observed in other regions consistent with distributions of shallow slow earthquakes and subducting seamounts interplate megathrust earthquakes have inflicted catastrophic damage on human society such an earthquake is predicted to occur in the near future along the nankai trough off southwestern japan an economically active and densely populated area in which megathrust earthquakes have already occurred1 2 3 4 5 megathrust earthquakes are the result of a plate subduction mechanism and occur at slip deficit regions also known as coupling regions 6 7 where friction prevents plates from slipping against each other and the accumulated energy is eventually released forcefully many studies have attempted to capture distributions of slip deficit rates sdrs in order to predict earthquakes8 9 10 however these studies could not obtain a complete view of the earthquake source region because they had no seafloor geodetic data the hydrographic and oceanographic department of the japan coast guard jhod has been developing a precise and sustainable seafloor geodetic observation network11 in this subduction zone to obtain information related to offshore sdrs here we present seafloor geodetic observation data and an offshore interplate sdr distribution model our data suggest that most offshore regions in this subduction zone have positive sdrs specifically our observations indicate previously unknown regions of high sdr that will be important for tsunami disaster mitigation and regions of low sdr that are consistent with distributions of shallow slow earthquakes and subducting seamounts this is the first direct evidence that coupling conditions might be related to these seismological and geological phenomena our findings provide information for inferring megathrust earthquake scenarios and interpreting research on the nankai trough subduction zone

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

contiguous rupture areas of two nankai trough earthquakes revealed by high resolution tsunami waveform inversion 1 we have developed a new method for inverting tsunami waveforms that reveals considerable detail in megathrust slip during subduction zone earthquakes previous methods have ensured compliance with the shallow water theory used to compute tsunami waveforms by using large subfaults that generate only long wavelength seafloor deformation we show that a better approach is to use small subfaults coupled with a smoothing criterion that ensures compliance with the shallow water approximation in an application of the method to historical earthquakes in the nankai trough southwestern japan we find that the areas with slip 1 m for the earthquakes of 1944 and 1946 which ruptured adjacent segments of the subduction zone are separated by a sharp non overlapping boundary this establishes that interseismic accumulation of strain energy extends very close to the boundary between rupture zones and strongly suggests that this boundary is associated with a physical barrier to rupture

viscoelastic relaxation following subduction earthquakes and its effects on afterslip determination afterslip is commonly thought to be the controlling process in postseismic deformation immediately following a great megathrust earthquake and is usually inferred from geodetic observations using purely elastic models however observed motion reversal of the near trench area right after the 2011 mw 9 tohoku oki earthquake demonstrates the dominance of viscoelastic relaxation of coseismically induced stresses to understand the importance of incorporating viscoelasticity in afterslip determination we employ biviscous burgers mantle rheology and use finite element models to explore how viscoelastic relaxation in short term postseismic deformation is controlled by various geometrical and rheological factors our results indicate that immediately after large megathrust earthquakes mw 8 0 viscoelastic deformation should always cause opposing motion of inland and trench areas and subsidence around landward termination of the rupture although the rate of such postseismic motion depends on local conditions such as the age and hence thickness of the slab and transient mantle viscosity values while elastic models may be adequate for afterslip estimation for earthquakes of mw 7 5 neglect of viscoelasticity for larger events leads to overestimate of afterslip downdip of the rupture and underestimate of afterslip at shallower depths reassessing shallow afterslip following the 2005 mw 8 7 nias earthquake using 2 d viscoelastic models suggests that the actual afterslip may be greater than that estimated using an elastic model by more than 50 similarly interpreting trenchward motion of some seafloor gps sites following the tohoku oki earthquake using a viscoelastic model suggests large shallow afterslip outside of the main rupture area

a subducted oceanic ridge influencing the nankai megathrust earthquake rupture megathrust earthquake rupture is highly influenced by seafloor bathymetric features such as oceanic fracture zones seamounts and ridges in convergent plate margins where these features subduct recent seismic reflection and refraction data reveal a trough parallel subducted oceanic ridge that is attached to the descending philippine sea plate beneath the accretionary wedge of the overriding eurasian plate in the eastern nankai trough subduction zone consisting of the tonankai and tokai segments the seismic survey data confirm the existence of subducted paleo zenisu ridge that was suggested by just magnetic data and as a result expands its distribution to the west the newly constrained subducted ridge that spans the two segments is estimated to be a maximum of 2 5 km high 20 30 km wide and 200 km long spatial mapping of the ridge shows that it is located roughly at the seaward edge of the coseismic rupture zone of the 1944 tonankai earthquake m 8 1 this ridge appears to be in close contact with the seaward end of the rigid backstop in the tonankai segment both the spatial correlation and the ridge backstop collision geometry suggest that the subducted ridge might be strongly mechanically coupled and may thus play a significant role as a seaward barrier inhibiting the 1944 earthquake rupture from propagating farther seaward

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

migrating tremor off southern kyushu as evidence for slow slip of a shallow subduction interface detection of shallow slow earthquakes offers insight into the near trench part of the subduction interface an important region in the development of great earthquake ruptures and tsunami generation ocean bottom monitoring of offshore seismicity off southern kyushu japan recorded a complete episode of low frequency tremor lasting for 1 month that was associated with very low frequency earthquake vlfe activity in the shallow plate interface the shallow tremor episode exhibited two migration modes reminiscent of deep tremor down dip of the seismogenic zone in some other subduction zones a large scale slower propagation mode and a rapid reversal mode these similarities in migration properties and the association with vlfes strongly suggest that both the shallow and deep tremor and vlfe may be triggered by the migration of episodic slow slip events

interplate locking condition derived from seafloor geodetic observation in the shallowest subduction segment at the central nankai trough japan we monitored seafloor crustal deformation at two observation stations on opposite sides of the nankai trough from 2013 to 2016 in order to investigate the interplate locking condition along the central nankai trough we estimated the seafloor crustal deformation with respect to the amurian plate based on five observations the results for two stations tca and toa were 38 25 mm yr toward n78 w and 57 21 mm yr toward n69 w 1 respectively the displacement rate at toa is consistent with the motion of the philippine sea plate with respect to the amurian plate using the euler vector of the revel model the displacement rate at tca is similar to that at other seafloor geodetic stations e g 48 10 mm yr at kum2 station on the kumano basin the interplate coupling rate was estimated to be roughly 70 40 1 in the shallowest segment of the nankai trough

the iberian roman humid period 2600 1600 cal yr bp in the zonar lake varve record andalucia southern spain abstract the iberian roman humid period irhp 2600 1600 cal yr bp is the most humid phase of the last 4000 yr in southern spain as recorded in the sedimentary sequence of zonar lake 37 29 00 n 4 41 22 w 300 m a s l a varve chronology supported by several ams 14 c dates allows study of the lake evolution at annual scale in response to human impact and climate changes there are four climate phases within this period i gradual transition 2600 2500 yr ago 650 550 bc from a previous arid period ii the most humid interval during the iberian early roman epoch 2500 2140 yr ago 550 190 bc iii an arid interval during the roman empire epoch 2140 1800 yr ago 190 bc ad 150 and iv a humid period synchronous with the decline of the roman empire 1800 1600 yr ago ad 150 350 varve thickness and geochemical proxies show a multi decadal cyclicity similar to modern north atlantic oscillation nao 60 20 years and solar variability cycles 11 yr the timing and the structure of this humid period is similar to that described in eastern mediterranean and northern european sites and supports the same large scale climate control for northern latitudes and the mediterranean region

interplate coupling along the nankai trough southwest japan inferred from inversion analyses of gps data effects of subducting plate geometry and spacing of hypothetical ocean bottom gps stations abstract we estimated the slip deficit rate distribution on the plate boundary between the subducting philippine sea plate and the continental amurian plate along the nankai trough southwest japan horizontal and vertical displacement rates were calculated from land based global positioning system gps data during the 5 year period from 1 january 2005 to 31 december 2009 we employed an inversion analysis of geodetic data using akaike s bayesian information criterion abic including an indirect prior constraint that slip distribution is smooth to some extent and a direct prior constraint that slip is mainly oriented in the plate convergent direction the results show that a large slip deficit exists at depths ranging from 15 to 20 km on the plate boundary in a belt like form the maximum slip deficit rate was identified off shikoku and reached 6 cm year the slip deficit rate differed by as much as 1 cm year when using a different geometric model of the subducting plate on the basis of the spatial distribution of estimation errors and the resolution of the obtained slip deficit rate on the plate boundary we also found that the offshore slip deficit rate cannot be estimated with sufficient accuracy using only land based gps data therefore we tested the improvement in results when introducing hypothetical ocean bottom gps stations the stations were arranged in four along arc and across arc spacings of 80 km and 40 km the ocean bottom data improved the estimation errors and resolutions and successful results were obtained for a checkerboard with each square 75 km 76 km our results indicate that 40 km along arc and across arc two dimensional spacing of ocean bottom gps stations is required to obtain reliable slip deficit distributions near the trough axis assuming the current estimation accuracy for ocean bottom horizontal displacement rates

geodetic data inversion using a bayesian information criterion for spatial distribution of fault slip summary we developed a new inversion method to reconstruct static images of seismic sources from geodetic data using akaike s bayesian information criterion abic coseismic surface displacements are generally related with a slip distribution on a fault surface by linear integral equations parametric expansion of the fault slip distribution by a finite number of known basis functions yields a set of observation equations expressed in a simple vector form incorporating prior constraints on the smoothness of slip distribution with the observation equations we construct a bayesian model with unknown hyperparameters the optimal values of the hyperparameters which control the structure of the bayesian model are objectively determined from observed data by using abic once the values of hyperparameters are determined we can use the maximum likelihood method to find the optimal distribution of fault slip we examined the validity of this method through a numerical experiment using theoretical data with random noise we analysed geodetic data associated with the 1946 nankaido earthquake ms 8 2 by using this method the result shows that the fault slip distribution of this earthquake has two main peaks of 4 and 6 m located off kii peninsula and muroto promontory these two high slip areas are clearly separated by a low slip zone extending along kii strait such a slip distribution corresponds with the fact that the rupture process of this earthquake in the western part is notably different from that in the eastern part

interplate coupling distribution along the nankai trough in southwest japan estimated from the block motion model based on onshore gnss and seafloor gnss a observations

interplate coupling off northeastern japan before the 2011 tohoku oki earthquake inferred from seafloor geodetic data 1 seafloor crustal movements off miyagi and fukushima prefectures northeastern japan observed for about 9 years before the 2011 tohoku oki earthquake m9 0 with the gps acoustic geodetic technique revealed the spatiotemporal variation of interplate coupling in this region off miyagi prefecture temporal variations of the crustal movements are characterized as a strain accumulation release process in relation to the 2005 miyagi oki earthquake m7 2 the intraplate velocity since december 2006 when the strain accumulation seemed to have restarted is 4 5 cm yr relative to the north american plate which is significantly lower than that before the 2005 event 6 7 cm yr this suggests that interplate coupling off miyagi prefecture since around 2007 is weaker than that before the 2005 event on the other hand off fukushima prefecture a westward crustal movement at a constant rate of about 2 cm yr relative to the north american plate has been observed for the interseismic period from 2002 to 2008 the interplate coupling off fukushima prefecture is significantly weak compared with that off miyagi prefecture this is consistent with the observed coseismic displacements associated with the 2011 event which are much smaller off fukushima prefecture than off miyagi prefecture