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

creep dike intrusion and magma chamber deflation model for the 2000 miyake eruption and the izu islands earthquakes 1 analysis of global positioning system data shows shrinkage of miyake island and the widening between nijima and kozu islands during the period of the miyake island volcanic activity and the ensuing izu islands earthquakes in 2000 the estimated time evolution of a model consisting of a dike creeping faults and a mogi source suggests that a crack opening on miyake island occurred immediately after the start of the seismic activities on 26 june and ended within several days at the west coast of miyake island after the seabed eruption on 27 june magma migrated from miyake island to kozu and nijima islands within several days the estimated volume of intruded magma totals around 1 2 109 m3 associated with the magma intrusion between miyake and kozu islands left lateral and right lateral creep motions occurred in regions off the west coast of miyake island and near kozu island the accumulated moment energy is equivalent to an earthquake of mw 6 6 and 6 6 for right lateral and left lateral creeping faults respectively the estimated magma chamber continued deflation beneath the southwestern part of miyake island from 26 june totaling around 0 12 109 m3 in volume change in addition to the collapse volume of 0 6 109 m3 at the summit of mount oyama on miyake island the volume change on miyake island can be compensated by the migrated magma toward kozu island from the deflation source beneath miyake island the deflation speed of the magma chamber beneath miyake island decreased and increased before and after the eruption of 14 15 july and 18 august suggesting a change in balance of mass influx and draining out rate of the magma chamber

dynamic modeling of slow slip coupled with tremor 1 we theoretically study the generation mechanism of slow slip in a dynamical framework assuming a fault in a fluid saturated thermoporoelastic medium the fluid flow is taken into consideration dynamic slip is assumed to create pores and cause shear heating on the fault key parameters in the modeling are su and su the nondimensional parameter su represents the relative dominance of the effect of pore creation on the fluid pressure change over that of shear heating while su is associated with the dominance of fluid flow effect over the effect of shear heating our calculation shows that we have to assume su 1 and relatively small values for su to simulate rupture speed that is negligibly small compared to the shear wave velocity although this was also found in our former paper our new finding here is the simulation of slow slip coupled with tremor we find that frozen slip is reactivated sporadically because the fluid inflow triggered by the pore creation elevates the fluid pressure on the fault the slip reactivation actually occurs if su is smaller than a threshold such sporadic reactivation of slips can be a model for slow slip coupled with tremor we also show that the moment evolution curves are categorized into two separate groups when su 0 1 one of them represents slow slips while the other represents ordinary earthquakes

a model for possible crustal deformation prior to a coming large interplate earthquake in the tokai district central japan we perform numerical simulations of a seismic cycle by applying a laboratory derived friction law to evaluate possible crustal deformations prior to the hypothesized tokai earthquake which is expected to occur in the near future along the suruga trough central japan the frictional force obeying a rate and state dependent friction law is assumed to act on the plate interface in a 2d model of the subduction zone we test two versions of the friction law the so called slowness version and the slip version we select model parameters on the basis of historical documents about past large earthquakes in the tokai district and the present coupling state of the plate interface beneath the tokai district estimated by gps observations simulation results for both the slowness and the slip version are as follows 1 the coupling region of the plate interface becomes narrower with time in the interseismic period 2 the inland crust contracts at a nearly constant rate for most of the interseismic period the contraction rate decreases or a change from contraction to extension takes place before the occurrence of a large interplate earthquake 3 significant abnormal crustal deformation precedes the earthquake and maximum amplitudes about one day before the earthquake exceed the noise levels in the case of clear weather of borehole strainmeters installed in the tokai district 4 the spatiotemporal variation of aseismic sliding on the plate interface perturbs the regional stress field around the source volume of the coming earthquake leading possibly to precursory seismic quiescence in the overriding plate and a change in focal mechanisms of small earthquakes in the subducting slab the most significant difference in the results between the slowness version and the slip version of the friction law is that amplitudes of preslip and crustal deformation just before earthquakes are several times larger for the slowness version than for the slip version although some ambiguity remains in the present model mainly because of the incompleteness of the friction law and the deficiency of observational data constraining model parameters the physical model can be improved through the comparison of predicted crustal deformation with observations continuous and concentrated observations of crustal deformation and seismic activity are thus important in the tokai district to understand quantitatively the sliding process preceding a large interplate earthquake there

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

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

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

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

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

the amurian plate motion and current plate kinematics in eastern asia we use global positioning system gps velocity data to model eastern asian plate kinematics out of 15 stations in korea russia china and japan studied here three sites considered to be on the stable interior of the hypothetical amurian plate showed eastward velocities as fast as 9 10 mm yr with respect to the eurasian plate they were stationary relative to each other to within 1 mm yr and these velocity vectors together with those of a few additional sites were used to accurately determine the instantaneous angular velocity euler vector of the amurian plate the predicted movement between the amurian and the north american plates is consistent with slip vectors along the eastern margin of the japan sea and sakhalin which reduces the necessity to postulate the existence of the okhotsk plate the euler vector of the amurian plate predicts left lateral movement along its boundary with the south china block consistent with neotectonic estimates of the displacement at the qinling fault possibly the southern boundary of the amurian plate the amurian plate offers a platform for models of interseismic strain buildup in southwest japan by the philippine sea plate subduction at the nankai trough slip vectors along the baikal rift the boundary between the amurian and the eurasian plates are largely inconsistent with the gps based euler vector suggesting an intrinsic difficulty in using earthquake slip vectors in continental rift zones for such studies

crustal deformation measurements in guerrero mexico 1 gps measurements of crustal deformation in guerrero southern mexico include surveys collected between 1992 and 2001 as well as continuous gps measurements at a few sites these geodetic observations are used to calculate interseismic deformation rates and assess the presence and possible location of transient deformation during the period encompassing 1992 25 to 2001 75 the data are used to examine transient deformation in 1998 previously described from data at a single site by lowry et al 2001 survey measurements and continuous data from a site near popocatepetl volcano confirm the 1998 transient and survey data also suggest another transient occurred following the 14 september 1995 mw 7 3 copala earthquake all of the available gps position estimates have been inverted for a combined model of slip during each event plus the steady state slip on the plate interface modeling of the steady state deformation rates confirms that the guerrero seismic gap is partially frictionally locked at depths shallower than about 25 km and accumulating strain that may eventually be released in a great earthquake the data also suggest that there is frictional coupling to much greater 40 km depths which releases more frequently in aseismic slip events the locations and sizes of the transient events are only partially constrained by the available data however the transient models which best fit the gps coordinate time series suggest that aseismic slip was centered downdip of the seismogenic portion of the plate bounding thrust in both events and the moment release had equivalent magnitudes mw 7 1 1 3 1 0 in 1995 1996 and 7 1 0 4 0 1 in 1998

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

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

bottom ablation and heat transfer coefficients from the 1983 marginal ice zone experiments bottom ablation in the marginal ice zone miz is a fundamental process that controls the ice edge position in both the winter and the summer during the east and west marginal ice zone experiments mizex west and mizex east in 1983 periodic sonic distance measurements between the overlying ice and transducers fixed on masts below ice floes determined the bottom ablation the melt rates for floes within 15 km of the ice edge ranged from near zero when the ice was in water at the freezing point to 0 5 m d 1 when the ice entered warm water greater than 3 k to the south simultaneous velocity and temperature measurements at 2 m below the ice in mizex west and at 2 m and 10 m below the ice in mizex east show the response of the melt rate to changing oceanographic conditions for the first time the combined oceanographic and ablation measurements allow the direct calculation of the bulk heat transfer coefficient ch between the ice and the ocean at 2 m and 10 m below the ice for the bering sea experiment ch was 8 10 4 while for the fram strait experiment ch varied from 2 10 4 to 4 10 4 within each set of experiments ch remained nearly constant over a wide range of melt rates relative ice water speeds and seawater temperatures

groundwater induced vertical movements observed in tsukuba japan 1 the anomalous vertical movements observed in tsukuba and their relevance to groundwater level changes are investigated first we investigated the vertical coordinate time series of an igs station tskb w r t a nearby stable site and found that the time series has a strong correlation with the groundwater level changes of the deep wells next we investigated those of the gps antenna attached at the tip of the antenna of tsukuba vlbi station w r t tskb we found that the time series is decomposed into components that have 1 high correlation with the groundwater level changes of the shallow wells and 2 high correlation with the air temperature poroelastic movements of aquifers due to groundwater level changes and thermal expansion of the vlbi antenna are likely for the mechanisms of these high correlations

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

reexamination of the interplate coupling in the tokai region central japan based on the gps data in 1997 2002 1 we re examined the interplate coupling in terms of backslip rate at the nankai suruga trough beneath the tokai region with a 3 dimensional gps time series and a refined plate boundary model we reanalyzed the gps data and reconstructed plate boundary configuration then we inverted gps velocities to infer the interplate coupling during april 1997 to april 2000 our results show that a maximum back slip rate of 2 cm yr was found at the depth of 15 25 km around 137 42e 34 32n we also estimated interplate coupling for the period from january 2001 to december 2002 this time period coincides with a slow slip event found by ozawa et al 2002 forward slip up to 3 cm yr was inferred beneath western region of lake hamana and we found that the epicenters of low frequency tremors are located there suggestive of a close connection between the occurrences of the slow slip event sse and low frequency tremors

inferring rate and state friction parameters from a rupture model of the 1995 hyogo ken nanbu kobe japan earthquake we consider the applicability of laboratory derived rate and state variable friction laws to the dynamic rupture of the 1995 kobe earthquake we analyze the shear stress and slip evolution of ide and takeo s 1997 dislocation model fitting the inferred stress change time histories by calculating the dynamic load and the instantaneous friction at a series of points within the rupture area for points exhibiting a fast weakening behavior the dieterich ruina friction law with values of dc 0 01 0 05 m for critical slip fits the stress change time series well this range of dc is 10 20 times smaller than the slip distance over which the stress is released dc which previous studies have equated with the slip weakening distance the limited resolution and low pass character of the strong motion inversion degrades the resolution of the frictional parameters and suggests that the actual dc is less than this value stress time series at points characterized by a slow weakening behavior are well fitted by the dieterich ruina friction law with values of dc 0 01 0 05 m the apparent fracture energy gc can be estimated from waveform inversions more stably than the other friction parameters we obtain a gc 1 5 l06 j m 2 for the 1995 kobe earthquake in agreement with estimates for previous earthquakes from this estimate and a plausible upper bound for the local rock strength we infer a lower bound for dc of about 0 008 m

a transient subduction zone slip episode in southwest japan observed by the nationwide gps array 1 we investigate the spatiotemporal variation of fault slip on the subduction interface in southwest japan following the two 1996 hyuganada earthquakes m 6 7 using continuous gps observations a silent thrust slip event has been reported by hirose et al 1999 following these earthquakes approximately 100 km to the north beneath the bungo channel we employ the network inversion filter to rigorously invert for the fault slip distribution in space and time the gps time series is modeled as a sum of 1 secular deformation 2 coseismic station displacements 3 transient fault slip 4 random benchmark motion 5 reference frame shifts and 6 observational errors nonnegativity constraints effectively prohibit normal faulting on the subduction interface spatial and temporal smoothing parameters are estimated by the extended kalman filter the estimated fault slip rate images postseismic slip following the two hyuganada earthquakes slip associated with the silent thrust event began roughly 1 month after the second earthquake but initiated 100 km to the northeast of the hyuganada earthquakes the slow event propagated southwest and downdip beneath the bungo channel lasting approximately 1 year with maximum slip rates of 0 6 m yr the equivalent seismic moment was mw 7 2 we can rule out the possibility that slip propagated from the source region of the hyuganada earthquakes to the location of the silent earthquake however the timing of the events suggests a causal connection perhaps due to static stress transfer this kind of transient event or silent earthquake may reflect different fault zone characteristics and may be responsible for accommodating strain that would otherwise be released in large earthquakes

evidence from the ad 2000 izu islands earthquake swarm that stressing rate governs seismicity magma intrusions and eruptions commonly produce abrupt changes in seismicity far from magma conduits that cannot be associated with the diffusion of pore fluids or heat such swarm seismicity also migrates with time and often exhibits a dog bone shaped distribution the largest earthquakes in swarms produce aftershocks that obey an omori type exponential temporal decay but the duration of the aftershock sequences is drastically reduced relative to normal earthquake activity here we use one of the most energetic swarms ever recorded to study the dependence of these properties on the stress imparted by a magma intrusion a 1 000 fold increase in seismicity rate and a 1 000 fold decrease in aftershock duration occurred during the two month long dyke intrusion we find that the seismicity rate is proportional to the calculated stressing rate and that the duration of aftershock sequences is inversely proportional to the stressing rate this behaviour is in accord with a laboratory based rate state constitutive law suggesting an explanation for the occurrence of earthquake swarms any sustained increase in stressing rate whether due to an intrusion extrusion or creep event should produce such seismological behaviour

a three dimensional simulation of crustal deformation accompanied by subduction in the tokai region central japan abstract a great earthquake is expected to occur along the suruga trough where the philippine sea plate subducts beneath the eurasian plate we estimate crustal deformation prior to this hypothetical earthquake called the tokai earthquake based on a simulation model for plate subduction a three dimensional extension of the models by stuart 1988 and kato and hirasawa 1996 in this model the time evolution of a dislocation field in an elastic half space is governed by a quasi static interaction induced by the dislocation field itself as well as by a rate and state dependent friction law acting on the plate interface observed geophysical constraints taken into account are the shapes of the curved subducting plate interface the recurrence interval of past great earthquakes 90 150 years the average seismic coupling coefficient 0 5 the annual rate of level change 5 mm year between the two bench marks at hamaoka and kakegawa and the backslip distribution on the plate interface estimated from the result of gps observation the simulation shows the following the occurrence of great earthquakes is approximately periodic during interseismic times a strongly coupled region is formed in a seismic zone and it shrinks as the next great earthquake approaches the strongly coupled region is confined to an area where the plate inclination is gentle the rupture of the earthquake starts at a point close to the maximum shear stress acting on the plate boundary subsidence of hamaoka relative to kakegawa changes to uplift several years before the earthquake volumetric strain undergoes a change from compression to extension or vice versa at certain observation sites several years before the earthquake changes in volumetric strain accelerate as the occurrence of the earthquake impends the maximum strain change for 1 day observed on the ground surface just before the earthquake is 10 8 to 10 7 a value about one tenth of the value predicted by a related two dimensional model the pattern of shear stress accumulation and the location of the preslip are affected by the shape of the plate interface

aseismic slip and low frequency earthquakes in the bungo channel southwestern japan 1 analysis of global positioning system gps data has shown transient crustal deformation in the bungo channel in southwestern japan since late august 2003 six years after a similar event in 1996 1997 considering the southeastward motion at many of the gps sites and the similarity between the 1996 1997 and 2003 events it is highly likely that the transients were caused by aseismic interplate slip between the philippine sea plate and the amurian plate the 2003 aseismic slip is estimated beneath the bungo channel and the relative slip increased with time on the west side with a moment magnitude mw amounting to 7 0 in contrast to the gradual subsidence of low frequency earthquakes which began and ended in coincidence with the 2003 event the 2003 transient crustal deformation proceeded at a roughly constant rate until the end of november 2003 the bungo channel area may release energy accumulated from the subduction of the philippine sea plate by aseismic slip

phosphorus speciation and its bioavailability in sediments of the jiaozhou bay abstract phosphorus p is an important macronutrient that can limit primary productivity in coastal marine ecosystems in this study four sediment cores were collected in the jiaozhou bay to study the phosphorus forms and their bioavailability including exchangeable or loosely sorbed p ex p iron bound p fe p authigenic p ca p detrital p de p and organic p op which were separated and quantified using a sequential extraction method sedex the results showed that the concentration of total p tp in core sediments ranged from 6 23 to 10 46 mol g and inorganic p ip was the dominated p form fe p and de p were the main chemical forms of ip in core sediments the profile variation of op presented the most significant among the phosphorus forms whereas the concentrations of ex p fe p and ca p varied slightly with depth indicating that the transformation of ex p fe p ca p and op could occur during sedimentary p burial moreover the distribution of p species was influenced by many factors including terrigenous input biological processes organic matter degradation and increasing human activities high total organic carbon toc op ratio occurred in the jiaozhou bay ranging from 73 to 472 average 180 81 in core sediments which was caused by the increasing terrestrial organic matter the ratio of toc p reactive ranged from 24 to 101 average 46 15 in core sediments lower than the redfield ratio implying a surplus of sedimentary reactive p compared with toc potential bioavailable p bap accounted for about 28 2 60 8 average 47 1 7 4 of tp in core sediments and presented an increasing trend since 1980s which might be responsible for the shift of phytoplankton community composition during these decades

aseismic slip transients emerge spontaneously in three dimensional rate and state modeling of subduction earthquake sequences 1 to investigate the possible physical mechanisms of recently observed aseismic slip events in the cascadia japan and mexico subduction zones we apply a dieterich ruina rate and state friction law to a three dimensional model of a shallow subduction fault that is loaded by imposed steady plate slip rate far downdip along the thrust interface friction properties are temperature and hence depth dependent such that sliding is stable at depths below about 30 km the system is perturbed into a significantly nonuniform slip mode along strike by introducing small along strike variations in the constitutive parameters a and a b in addition to large heterogeneous earthquake slip at seismogenic depths and associated postseismic transients we found that slip events which have clearly aseismic slip rates emerge spontaneously around the downdip end of the seismogenic zone both transients which start well after a seismic event and those which are triggered by other transients are observed from the simulations the slip velocity depth range and sometimes along strike migration speed of simulated transients are similar to the observations from natural subduction zones unstable stable transitional friction properties near the downdip end of the seismogenic zone are suggested to be an ingredient allowing such transients simulated transients can weaken the locking intensity of the updip seismogenic zone while enhancing that of the transition zone spatial temporal correlation of aseismic transients and nearby seismicity in the guerrero mexico area suggests that transients may signal a period of increased probability for nucleating their high frequency counterparts as damaging subduction thrust events

periodic slow earthquakes from the cascadia subduction zone continuous geodetic measurements from convergent margins have shown that deep transient creep events can release large amounts of strain energy without detectable seismic shaking and they are thus known as slow or silent earthquakes because subduction zones generate the largest earthquakes

stress breakdown time and slip weakening distance inferred from slip velocity functions on earthquake faults we estimate the critical slip weakening distance on earthquake faults by using a new approach which is independent of the estimate of fracture energy or radiated seismic energy the approach is to find a physically based relation between the breakdown time of shear stress tb the time of peak slip velocity tpv and the slip weakening distance dc from the time histories of shear stress slip and slip velocity at each point on the fault which can be obtained from dynamic rupture calculations using a simple slip weakening friction law numerical calculations are carried out for a dynamic shear crack propagating either spontaneously or at a fixed rupture velocity on a vertical fault located in a 3d half space and a more realistic horizontally layered structure with finite difference schemes the results show that tpv is well correlated with tb for faults even with a heterogeneous stress drop dis tribution except at locations near strong barriers and the fault edges we also inves tigate this relation for different types of slip weakening behavior we have applied the method to two recent strike slip earthquakes in western japan the 2000 tottori and the 1995 kobe events we integrated the slip velocity functions on the vertical fault obtained from kinematic waveform inversion of strong motion and teleseismic records from the arrival time of rupture tr to the time of the peak slip velocity tpv and we then corrected the slip obtained at tpv for the errors expected from the dynamic calculations it was found that the slip weakening dis tance d c estimated in the frequency window between 0 05 and 0 5 hz ranges between 40 and 90 cm on the two earthquake faults however if we consider the limited frequency resolution of the observed waveforms probable time errors in the slip velocity functions obtained from kinematic inversion and the uncertainty of the slip weakening behavior the above estimates may be those located between the minimum resolvable limit and the upper bound of their real values the estimated dc values do not necessarily seem to indicate larger values in the shallower part and smaller values in the deeper part of the fault but rather a spatially heterogeneous distribution that appears to be dependent on the local maximum slip this possible dependence might be interpreted by the frictional properties of the fault such as the degree of roughness or the thickness of gouge layers in addition to stress heterogeneities

episodic aseismic slip in a two degree of freedom block spring model 1 we consider a two degree of freedom block spring model in which two blocks block 1 and block 2 are connected by a spring and driven by a slowly moving driver assuming a rate and state dependent friction law we set the friction parameters such that dynamic instability occurs at block 1 episodic aseismic slip occurs at block 2 when its frictional parameters are near the stability transition when the stress has accumulated to approximately a steady state level during an interseismic period block 2 starts a slow slip quasi static oscillation in the stress and slip velocity occurs with decaying fluctuation amplitudes leading to the steady state values the decaying oscillation could be a plausible generation mechanism of the episodic aseismic slip observed in the tokai district japan since 2001 we also consider various slip modes on a plate boundary based on this two block model associated with the interaction between different frictional properties

a dislocation model of strain accumulation and release at a subduction zone strain accumulation and release at a subduction zone are attributed to stick slip on the main thrust zone and steady aseismic slip on the remainder of the plate interface this process can be described as a superposition of steady state subduction and a repetitive cycle of slip on the main thrust zone consisting of steady normal slip at the plate convergence rate plus occasional thrust events that recover the accumulated normal slip because steady state subduction does not contribute to the deformation at the free surface deformation observed there is completely equivalent to that produced by the slip cycle alone the response to that slip is simply the response of a particular earth model to embedded dislocations for a purely elastic earth model the deformation cycle consists of a coseismic offset followed by a linear in time recovery to the initial value during the interval between earthquakes for an elastic viscoelastic earth model elastic lithosphere over a viscoelastic asthenosphere the postearthquake recovery is not linear in time records of local uplift as a function of time indicate that the long term postseimic recovery is approximately linear suggesting that elastic earth models are adequate to describe the deformation cycle however the deformation predicted for amore simple elastic half space earth does not reproduce the deformation observed along the subduction zones in japna at all well if stick slip is restricted to the main thrust zone as recognized earlier by shimazaki seno and kato the uplift profiles could be explained if stick slips were postulated to extend along the plate interface beyond the main thrust zone to a depth of perhaps 100 km but independent evidence suggests that stick slip at such depths if unlikely less

interplate coupling and a recent aseismic slow slip event in the guerrero seismic gap of the mexican subduction zone as deduced from gps data inversion using a bayesian information criterion a large scale slow slip event with a magnitude equivalent to mw 7 4 has been observed at seven continuous gps stations located in the guerrero oaxaca region southern mexico for several months from late 2001 to middle 2002 geophys res lett 2003 30 doi 10 1029 2003gl017219 we re analyzed the gps time series data to estimate the displacements associated with the slow slip event and also the displacement rates during the interseismic period prior to this event by applying an inversion technique using a bayesian information criterion abic we then carried out gps data inversion again with abic and some detailed forward modeling to obtain spatial distributions of the back slip rates and the slow slip on a 3 d curved plate interface between the subducting cocos and the overriding north america plates the results show that the average direction of the back slip rates is n31 3 e 5 6 which is congruent with that of plate convergence in this region interplate coupling is found to be very strong down to a depth of about 45 km indicating a coupling ratio of 0 83 0 86 except for a couple of segments on the model region and decreases dramatically down below the average direction of the slow slip is oriented about 20 35 counterclockwise from the opposite direction of the plate convergence the slow slip detected on the mid depth segment to the upper rim of the model region reaches about 9 18 cm in the landward region of the guerrero seismic gap from inversion and forward modeling from these results we conclude it is possible that the slow slip may have invaded a deeper part of the strongly coupled seismogenic zone at least up to a depth of about 25 km we also estimate stress changes due to the slow slip event some decrease in shear stress on the plate interface at these depths suggests that if such a slow slip event occurred episodically it is possible that the time of occurrence of a forthcoming large earthquake in the guerrero gap would be delayed to some extent 2004 elsevier b v all rights reserved

time sequence and the recurrence models for large earthquakes along the nankai trough revisited it is suggested that time sequence of earthquakes can be explained by the time predictable recurrence model rather than the slip predictable recurrence model however the reliability of the model depends primarily on data accuracy missing large events seriously affect the evaluation of the models although the time predictable model can explain the recent three large events along the nankai trough back to a d 1707 there was serious discrepancy when the model was applied to older events recent archeological studies have discovered new events along the trough missed in historical documents i found that with the addition of the archeologically discovered new events the recurrence models can be applied to older events and that the time sequence including these new events suggests a time predictable recurrence pattern over a 1000 year interval

interplate coupling in the tokai district central japan deduced from continuous gps data i invert gps displacement rates in the tokai district to investigate strain accumulation associated with the anticipated tokai earthquake i apply a representation of interseismic strain accumulation at subduction zones by savage 1983 and estimate a distribution of virtual normal fault slip back slip on the plate boundary surface estimated back slip takes its maximum value of 30 40mm year under the sea of enshu this value is nearly equal to the relative plate motion there implying almost complete coupling back slip is smaller under suruga bay and its direction is different from the relative motion between the eurasian and the philippine sea plates localized deformation at the northern tip of the philippine sea plate may be responsible for this discrepancy partitioning tectonic strain due to the plate convergence into faults on both sides of the izu peninsula and also distributed strain inside the peninsula

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

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

earthquake deformation cycle on the san andreas fault near parkfield california six moderate earthquakes are thought to have ruptured the parkfield segment of the san andreas fault since 1857 the similar characteristics of the three seismically recorded events together with the quasi regular 22 year recurrence interval have led to the forecast of a similar event in 1988 5 years in this study the potential for the hypothesized earthquake is assessed by estimating the time required for interseismic straining to recover the strain energy released by the most recent june 1966 parkfield earthquake for a simple model of the earthquake cycle this interval is proportional to the ratio of the 1966 seismic moment to the interseismic moment deficit rate baseline lengths measured before and after the 1966 earthquake are inverted to estimate the magnitude and distribution of the combined coseismic and transient postseismic slip although the geodetic data determine only broad spatial averages of the fault slip they do require that slip at depth exceeded the surface offsets measured in 1966 inversions with extreme prior models are calculated to assess the range of seismic moment and moment deficit rates consistent with the available geodetic data inversions assuming only that the slip distributions are to some degree smooth yield strain energy recovery intervals of 14 25 years extreme values range from as little as 6 years to as much as 29 years in comparison historic recurrence intervals of parkfield earthquakes range from 12 to 32 years these results are consistent with the expectation of a magnitude 5 6 earthquake near parkfield by 1993

geometry and relative motion of the philippine sea plate and pacific plate beneath the kanto tokai district japan the recent acquisition of high density and improved seismic data by the kanto tokai k t observational network of the national research institute of earth science and disaster prevention requires the revision of conventional plate configuration models for the k t district we propose a new interpretation of the configuration and relative motion of the philippine sea phs plate pacific pac plate and eurasian eur plate on the basis of the distribution of hypocenters velocity structure and focal mechanisms in the k t district the new model for the configuration of the phs and pac slabs clearly delineates the phs slab subducting northwestward beneath the k t district from the sagami and suruga troughs and the pac slab subducting westward beneath the phs slab from the japan trench the thickness of the descending phs slab is estimated to be 30 5 km the proposed configuration of the phs slab is significantly different from those obtained by other researchers including our own previous study the new model is fully consistent with global plate motion data the new model leads to an interpretation of the tectonic processes taking place beneath the k t district for the sagami trough wing of the phs slab the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the pac slab the southwestern portion carrying the izu peninsula has been bent upward because of its buoyancy producing the observed contorted shape for the suruga trough wing the dip direction of the phs slab gradually changes from northwestward at the eastern portion to northward at the western portion the new model also indicates the presence of offset within the phs slab between the sagami and suruga trough wings this area is characterized by a low level of seismic activity the absence of a high velocity structure and the presence of quaternary volcanoes it seems reasonable to speculate that the distribution of quaternary volcanic edifice construction is controlled by the location of the offset within the phs slab in view of this new model the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined

transient fault slip in guerrero southern mexico the guerrero region of southern mexico has ac cumulated more than 5 m of relative plate motion since the last major earthquake in early 1998 a continuous gps site in guerrero recorded a transient displacement modeling indicates that anomalous fault slip propagated from east to west along strike of the subduction megathrust campaign gps and leveling data corroborate the model the moment release was equivalent to an mw 6 5 earthquake no m 5 earthquakes accompanied the event indicating the frictional regime is velocity strengthening at the location of slip

determination of constitutive relations of fault slip based on seismic wave analysis constitutive laws define the boundary conditions on fault plane and govern many aspects of earthquake failure although several constitutive laws have been formulated based on laboratory rock experiments and applied to theoretical studies in various fields no actual relation during a natural earthquake has been determined the 1995 kobe earthquake is suitable for detailed kinematic analysis and this enables the first evaluation of constitutive relations for a natural earthquake in this study we determine spatiotemporal slip distribution on an assumed fault plane of the 1995 kobe earthquake by waveform inversion and then solve elastodynamic equations using a finite difference method to determine the stress distribution and constitutive relations on the fault plane an inversion method based on bayes theorem is employed to obtain a spatiotemporal slip distribution and enables us to ensure the objective uniqueness of the solution with numerous parameters and smoothing constraints this slip distribution is then used as part of the boundary condition in the finite difference calculation the time histories of slip and shear stress obtained then provide a constitutive relation at each point on the fault plane they show slip weakening relations almost everywhere on the fault plane while slip rate dependency is not clear the slip weakening behavior has a clear depth dependency indicating that the slip weakening rate d du is smaller in the shallow crust than that in the deep crust this may be associated with the paucity of shallow seismicity observed in the source region of this earthquake as reported for many mature fault systems

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

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

focal zone of a future tokai earthquake inferred from the seismicity pattern around the plate interface abstract a future large tokai earthquake has been considered to be the most urgent problem of impending disasters in the central part of the japanese islands since the first warning was announced in 1976 recent progress in observations has provided a great amount of data thus making a detailed investigation possible in this study based on the seismicity and the focal mechanism patterns of microearthquake data the mechanical situation that governs plate interactions around the tokai district was investigated it was found that the seismicity in the subducting philippine sea slab is composed of three characteristic groups of activities intense activity beneath lake hamana a linear cluster extending from lake hamana toward the northwest and a broad cluster expanding over the inland area in the west of suruga bay we propose that these activities occur inside the subducting oceanic crust and reflect the present stress state acting there the mechanism inducing these activities is assumed to come from two stress sources the lateral stretching of the slab and the partial locking between both plates this interpretation leads to the hypothesis that the broad cluster in the west of suruga bay represents a stress concentration due to locking the activity beneath lake hamana is proposed to represent shearing motion induced there and is interpreted to form the boundary between the rupture zones of the 1944 tonankai earthquake and a future large tokai earthquake these analyses resulted in identifying the wide inland area extending from the west coast of suruga bay to lake hamana to be a focal zone of a future tokai earthquake the zone proposed in this study indicates a significant deviation in its strike from the original model proposed by ishibashi in that the former parallels the nankai trough while the latter parallels the suruga trough

geodetic data inversion using abic to estimate slip history during one earthquake cycle with viscoelastic slip response functions summary we developed a new method of geodetic data inversion to estimate slip history at a plate interface by using akaike s bayesian information criterion abic in this method we considered the effects of viscoelastic stress relaxation in the asthenosphere which cannot be neglected to estimate slip history at a plate interface during one earthquake cycle we also introduced a proper formulation to incorporate two sorts of partially dependent prior information into observed data by bayes rule by applying the new inversion method to levelling data for 1893 1983 in shikoku southwestern japan we reconstructed the pattern of space time variation in slip motion during one earthquake cycle including the 1946 nankai earthquake at the interface between the eurasian and the philippine sea plates the result shows that a steady slip motion at a plate convergence rate 40 mm yr 1 proceeds in the shallow and the deep regions through the entire earthquake cycle in the intermediate depth range 10 30 km on the other hand an instantaneous slip of approximately 4 m occurs at the time of the nankai earthquake after that this portion keeps in stationary contact until the occurrence of the next nankai earthquake if we neglect the effects of viscoelastic stress relaxation the inversion analysis gives geophysically unrealistic results

plate convergence and long term crustal deformation in central japan surveys by continuous global positioning system in and around japan revealed that the amurian plate collides with the north american plate in central japan by 2 cm yr long term crustal deformation seems to be influenced mainly by this collision although subduction of oceanic plates governs short term elastic deformation over the arc here we study the long term deformation field by carefully removing the short term signals inferred from a priori plate convergence vectors and coupling strengths predicted by a thermal model the obtained field shows that the change in velocities occurs along the longitude 135 137 and there exist a relatively rigid block and zones accommodating strains characteristic compressional deformation is found northwest of izu due possibly to the collision of the izu bonin arc with honshu plate convergence rate along the nankai suruga trough is considerably smaller in eastern parts due partly to the transition from the amurian to the north american plate of the landward side and partly to the motion of the izu microplate relative to the philippine sea plate this accounts for longer recurrence intervals of interplate earthquakes in the suruga trough where the tokai earthquake is anticipated to occur

spatiotemporal evolution of a transient slip event on the san andreas fault near parkfield california 1 in 1993 several baselines of the two color electronic distance meter edm network at parkfield california deviated from their long term rates coincident with anomalous observations from nearby strain meters and a creep meter as well as an increase in microseismicity between october 1992 and december 1994 three m 4 5 earthquakes occurred beneath middle mountain near the hypocenter of the 1934 and 1966 parkfield m6 events we analyzed the two color edm data using a kalman filtering based technique to image the spatiotemporal evolution of slip on the fault at parkfield between the mid 1980s and 2003 this method accounts for localized random walk motion of the geodetic monuments and a prominent seasonal signal that affects many baselines we find that a slip rate increase occurred between january 1993 and july 1996 on the upper 8 km of the fault near middle mountain the peak estimated slip rate during this time was 49 mm yr which exceeds the long term geologic rate of 35 mm yr the slip rate evolution appears episodic with an initial modest increase after the m4 3 earthquake and a much larger jump following the shallower m4 7 event in december 1994 this temporal correlation between inferred slip and seismicity suggests that the moderate earthquakes triggered the aseismic fault slip the edm data cannot resolve whether transient slip propagated across the nucleation zone of the 1934 and 1966 m6 parkfield earthquakes however transient slip and its associated stress release in the hypocentral area of previous parkfield events is consistent with the nucleation of the 2004 m6 parkfield earthquake elsewhere on the fault

on the physical mechanism of silent slip events along the deeper part of the seismogenic zone 1 to investigate the mechanism of recently observed silent slip events we simulated earthquake preparation processes using the dieterich ruina rate and state dependent friction law to ensure realistic modeling of the unstable stable transition we considered small cut off velocity to an evolution effect in the friction law for the transition zone when the cut off velocity to the evolution effect is significantly smaller than that of a direct effect steady state friction behaves as velocity weakening at low slip velocity and velocity strengthening at high slip velocity this frictional behavior was experimentally and theoretically confirmed for the unstable stable transition zone the results of our numerical simulations show that silent slips of which velocity is higher than the velocity of relative plate motion eventually propagates horizontally along the unstable stable transition over a period of several years silent slip events can be interpreted as being caused by the transitional behavior of the fault constitutive law