precursory seismic quiescence before the 1994 kurile earthquake mw 8 3 revealed by three independent seismic catalogs we have found that the m w 8 3 kurile earthquake on october 4 1994 followed an outstanding seismic quiescence starting 5 6 years before the mainshock near the ruptured area we have analyzed three independent seismic catalogs institute of seismology and volcanology hokkaido university isv japan meteorological agency jma and international seismology center isc in spite of selecting different magnitude bands and time windows all three catalogs presented the common feature of the seismic quiescence this fact strongly suggests that the seismic quiescence should not be a man made change but actually occurred moreover we have confirmed that the seismic quiescence was the most significant and the earthquake was the largest in the past twenty five years in this region therefore we confidently interpret this seismic quiescence as an indication of a preparation process for the m w 8 3 kurile earthquake

aftershock sequence of the 1994 mw 6 8 liwa earthquake indonesia seismic rupture process in a volcanic arc we present the aftershock activity following the february 15 1994 mw 6 8 earthquake which was strongly felt in southern sumatra indonesia near the great sumatran fault gsf at this place the slip rate is supposed to be low neverthless three m 6 events occurred along this segment during this century no significant instrumental microseismicity has ever been recorded there we use data from both the regional indonesian network and a local seismic array operating 11 days after the mainshock during one month aftershocks mostly locate in a broad zone of 55 20 km near two active nw trending strike slip segments of the gsf separated by a recent caldera suwoh during the experiment the nw segment from suwoh up to 15 km se of the ranau lake caldera an old right stepover pull apart was very active as first suggested by the aftershock distribution and the lack of coseismic rupture at the surface the 20 focal mechanisms determined provide evidence for various post seismic stress adjustments on secondary faults located in the ranau suwoh paleo pull apart graben less than 20 of the aftershocks are directly linked to the main rupture a nearly pure right lateral strike slip faulting reaching 25 km depth a narrow seismic gap underlines the active volcanic area of suwoh we conclude that the rupture process along the gsf is controlled both by volcanism and structures and that the volcanic activity affects the mechanical properties of the crust only in a narrow zone

rapid determination of global moment tensor solutions in an effort to improve data services the national earthquake information center has begun a program in cooperation with the incorporated research institutions for seismology data management center iris dmc to produce rapid estimates of the seismic moment tensor for most earthquakes with a body wave magnitude of 5 8 or greater although this program is still undergoing testing and fine tuning an estimate of the moment tensor can usually be produced within 20 minutes of the arrival of the broadband p waveform data from the iris dmc although the speed with which this data can be obtained varies in many cases a solution can be obtained within two hours of the earthquake these solutions do not vary significantly from the final solutions determined using the entire network because of the manner in which the data and the synthetic seismograms are aligned the method is insensitive to the effects of timing errors epicentral mislocation and lateral heterogeneity in earth structure this procedure was implemented in may 1993 the results from that month are presented here

aftershocks of the andreanof islands earthquake of june 10 1996 and local seismotectonics three questions have been addressed in connection with an mw 7 7 earthquake that occurred in the andreanof islands alaska on june 10 1996 first was there any variation in seismic activity rate during the previous five years that might have been diagnostic of the imminent occurrence of this event the answer based on the usgs pde catalog is no second though there were abundant pre event earthquakes and aftershocks on both sides of adak canyon why was there very little activity under the canyon itself a property that has been observed previously it is not possible to resolve the cause of the behavior with existing seismological data finally how does one explain the eastern group of aftershocks which fell within the zone of abundant aftershocks of the 1986 mw 8 andreanof islands earthquake when very little of the 1996 mainshock moment was released under or to the east of adak canyon one explanation of these aftershocks is that the recent aftershocks are late aftershocks of 1986 whose occurrence within a short time was induced by the stress pulse but not seismic slip from the 1996 earthquake though large earthquakes in the aleutians occur in distinct tectonic blocks the boundaries of these blocks may not always be defined reliably by aftershock zones

source spectral characteristics of two large intra slab earthquakes along the southern kurile hokkaido arc abstract in 1993 and 1994 two large earthquakes occurred along the southern kurile hokkaido arc the 1993 kushiro oki earthquake 15 january mw 7 6 and the 1994 shikotan earthquake 4 october mw 8 2 these were intra slab earthquakes that ruptured through a substantial part of the subducting oceanic lithosphere we study source spectral characteristics of these large intra slab earthquakes based on strong motion records for the kushiro oki earthquake the s wave spectra on three rock site stations are directly compared with the theoretical spectra based on the omega squared source model and the source parameters estimated from long period seismic waves the observed spectra are roughly consistent with the theoretical ones at low frequencies

earthquake history of the sumatran fault indonesia since 1892 derived from relocation of large earthquakes abstract we map the fault planes of m 7 0 earthquakes along the sumatran fault in sumatra western indonesia for the period since 1892 to obtain precise hypocenter locations of large earthquakes and identify fault planes of m 7 0 earthquakes we relocated 27 m 6 0 earthquakes from 1921 to 2012 using the modified joint hypocenter determination method we found that six m 7 0 events appear to have occurred on segments of the sumatran fault as follows kumering for the 1933 m s 7 5 event the northwestern and southeastern parts of tripa for the 1935 m s 7 0 and 1936 m s 7 2 events respectively the southeastern half of sunda for the april 1943 m s 7 1 event ketaun for the first m s 7 3 event of the june 1943 doublet and suliti and sumani for the second m s 7 6 event of the june 1943 doublet we also identified the faults of four m 7 0 earthquakes between 1892 and 1920 by using information on crustal deformation and damage distributions from the results of earthquake locations between 1892 and 2012 and the corresponding fault lengths of m 7 0 earthquakes we have interpreted the large m 7 0 earthquake history of the sumatran fault for the past 120 years possible seismic gaps for m 7 0 earthquakes along the sumatran fault are the northern half of the sunda segment and the semangko dikit sianok barumun toru renun aceh and seulimeum segments

mean sea surface and variability of the gulf of mexico using geosat altimetry data geosat exact repeat mission erm altimetric measurements of the sea surface height in the gulf of mexico are used to determine the mean sea surface height with respect to the ellipsoid and mesoscale variability along geosat ground tracks in the gulf for the time period from november 8 1986 to november 25 1988 the alongtrack mean sea surface is determined using a regional crossover adjustment procedure in which the tilt and bias of mean arcs are estimated using a least squares technique to minimize the height differences at crossovers points a mean surface generated using the geosat erm alongtrack mean is calculated and contrasted with a previously derived mean surface determined using geos 3 and seasat crossover differences this provides a first look at the variability in the mean between the time periods of 1987 1988 and 1975 1978 in addition the alongtrack mesoscale variability time series has been produced from the geosat erm data set by using a robust orbit error removal algorithm to determine the variability of the sea surface height with respect to the alongtrack mean a surface generated using the rms of this alongtrack time series shows good qualitative and quantitative agreement with previous in situ observations in the region this study demonstrates the potential of satellite altimetry for oceanographic studies of the gulf of mexico

geodetic inversion for the fault model of the 1994 shikotan earthquake the fault parameters of the 1994 shikotan earthquake were determined by inverting all available geodetic data using an iterative linearized least squares method a one fault inversion shows that a shallow dip fault plane model does not reproduce the minor deformation observed on shikotan island while a steep dip model can fit all the data well multifault inversion shows that a fault plane divided into two subfaults lengthwise is the best fitting model based on akaike s information criteria aic for shallow dip faulting mechanism this model yields a very high stress drop 40 mpa on the deeper subfault for a steep dip model a fault plane divided into two subfaults sideways gives the minimum aic all the computations for models consisting of two to eight subfaults show that the chi square values of the shallow dip models are about 10 higher than those of the steep dip models considering the high stress drop the larger chi square value and the requirements of a complex subfault system for the shallow dip model we reach the conclusion that the steep dip model is more suitable to explain the geodetic observations

dynamic transfer of simulated altimeter data into subsurface information by a numerical ocean model a global eddy resolving capability to predict the ocean circulation is technologically feasible within the next decade for this purpose the satellite altimeter is the most promising operational source of oceanic data with global coverage but only at the surface a comparable source of subsurface data is not on the horizon this investigation demonstrates the ability of a numerical ocean model to dynamically transfer simulated altimeter data into subsurface information this was done for a variety of dynamical regimes with 1 barotropic baroclinic mixed and episodic instabilities 2 flat bottoms or large amplitude topography 3 relatively vigorous or gentle exchange of energy between the layers and 4 major time scales that are short 60 days long 1 year or both in all cases the pattern of the deep pressure field is much different from the one for the current related variations in the sea surface elevation and sometimes not obviously related to it the model was able to reconstruct the deep pressure field even in situations with energetic shallow and deep circulations baroclinic instability and a vigorous vertical exchange of energy however in such experiments the frequency of updating for the free surface elevation was critical in this study the maximum update interval that allowed successful dynamic surface to subsurface transfer was about half the shortest major time scale smts e g 50 60 days in the experiments with baroclinic instability without knowledge of the deep pressure field numerical predictions of the surface pressure field and the depth of the pycnocline typically were better than climatology for 1 4 to 1 2 the smts but with successful dynamic surface to subsurface transfer forecasts without updating were better than climatology for the smts or more the time scale for predictive skill can be substantially longer than the maximum update interval permitted because the update interval must be short enough to allow decreasing error in the deep pressure field from one free surface update to the next until the error asymptotes at some acceptable level approximately 30 50 in these results forecasts of nondispersive isolated eddies with beta rossby number o 1 demonstrated predictive skill for 3 months or more even when the subsurface initial state was unknown a serendipitous result of the study is some progress in understanding the generation of cyclonic eddies associated with the loop current in the eastern gulf of mexico section 5 5

eddy energy of the northwest atlantic and gulf of mexico determined from geos 3 altimetry from may 1975 to october 1978 the geos 3 satellite altimeter made numerous repeated observations of sea surface topography in the northwest atlantic and gulf of mexico by comparing members of about 1000 collinear pairs of altimeter profiles we have determined mesoscale sea height variability and eddy kinetic energy in these ocean regions our results agree qualitatively with estimates made from traditional oceanographic surveys but significant quantitative differences exist in certain areas especially in the gulf stream between florida and cape hatteras where the altimetric results show less variability the reason for this appears to be due to differences in spatial sampling historical oceanographic measurements are relatively sparse and must be aggregrated into small geographic boxes to compute variability statistics results therefore represent a combination of temporal and spatial variability in contrast repeated satellite altimeter tracks provide point measurements of changes of sea height and slope this enables determination of temporal variability alone a quantity more representative of eddy energy it is important to make this distinction between space and time because in regions of strong horizontal gradient such as the gulf stream spatial variability can exceed the temporal component in mid ocean where spatial variability is negligible altimetric and oceanographic results are in excellent agreement

newly imaged shape of the deep seismic zone within the subducting pacific plate beneath the hokkaido corner japan kurile arc arc junction 1 the geometry of the deep seismic zone associated with the subducting pacific plate beneath the north american plate in the hokkaido corner japan kurile arc arc junction has been investigated based on the hypocenters accurately relocated by a dense local seismographic network with three dimensional p and s wave velocity structures the model suggests that the lateral changes in the dip of the subduction zone are more rapid than previously believed we found that the deep seismic zone in the pacific plate dips at 20 to 30 on the side of the japan arc the dip angle increased in a narrow region around 143 144 e by 10 to 20 and the dip was 40 to 50 on the side of the kurile arc in the transitional zone around 143 144 e an unusual distribution of microearthquakes has been discovered within the pacific plate which was located on a near vertical plane with an area of 50 100 km2 with strike that was perpendicular to the kurile trench axis this feature was named the tokachi oki slab cracking zone we suggest that this is a slab cracking zone torn by the extensional stress due to the rapid lateral changes in the dip of the subduction zone the slab cracking zone may possibly grow into the large disruption or tear of the slab in the future

evolution of a warm core ring in the gulf of mexico lagrangian observations during 1985 and 1986 a gulf of mexico ring shed by the loop current was observed to migrate toward the western gulf of mexico this movement across the gulf was well documented by observations that included drifter data within and outside the ring sea surface temperature at weekly intervals expendable bathythermograph surveys at various times one major hydrographic cruise when the ring was in the northwestern gulf and currents from moorings over which the ring passed the drifter data were used to infer the movement of the ring center as well as the eccentricity and orientation of the major axes the data from the drifters bridge the gaps between detailed surveys to the extent that a daily history of the position and shape of the ring can be constructed the synthesis of these diverse but complimentary data sources provides a detailed description of how the ring interacted with the bathymetry of the northern gulf of mexico as well as with previously and subsequently shed rings

absence of earthquake correlation with earth tides an indication of high preseismic fault stress rate because the rate of stress change from the earth tides exceeds that from tectonic stress accumulation tidal triggering of earthquakes would be expected if the final hours of loading of the fault were at the tectonic rate and if rupture began soon after the achievement of a critical stress level we analyze the tidal stresses and stress rates on the fault planes and at the times of 13 042 earthquakes which are so close to the san andreas and calaveras faults in california that we may take the fault plane to be known we find that the stresses and stress rates from earth tides at the times of earthquakes are distributed in the same way as tidal stresses and stress rates at random times while the rate of earthquakes when the tidal stress promotes failure is 2 higher than when the stress does not this difference in rate is not statistically significant this lack of tidal triggering implies that preseismic stress rates in the nucleation zones of earthquakes are at least 0 15 bar h just preceding seismic failure much above the long term tectonic stress rate of 10 4 bar h

a review of numerical ocean modeling 1983 1986 midlatitude mesoscale and gyre scale for the years 1983 to the present numerical modeling of midlatitude ocean circulation on the mesoscale and gyre scale is reviewed numerical results have shown great similarity to recent thermocline theories but also some important differences in particular ventilation of the pool zone caused by convective processes is substantial also solutions employing explicitly resolved eddies differ significantly from their equilibrium counterparts inverse methods have provided improved estimates of meridional heat transport and tropical upwelling of tracers the crucial influence of the western boundary on the circulation of the gyre interior is beginning to be understood research has focused on the conditions for radiation by jets the relationship between a jet s structure and its stability and the generation of deep mean flows by eddy activity near the surface constraints on the structure of isolated vortices imposed by instability mechanisms have been explored with new balanced models which provide an inexpensive but accurate alternative to primitive equation models for many oceanic processes transport of salinity by gulf stream rings has been found to be comparable to the effects of evaporation and precipitation in the slope water it has also been shown that radial circulation in warm core rings cannot be disregarded as a possible cause of ring spin down in anticipation of a dramatic increase in the oceanic observational data base from altimetry scatterometry tomography and in situ measurement new modeling techniques for data assimilation and prediction are beginning to be developed

a dimensional analysis method for improved load unload response ratio the load unload response ratio lurr method is proposed to measure the damage extent of source media and the criticality of earthquake before the occurrence of a large earthquake anomalous increase in the time series of lurr within the certain temporal and spatial windows has often been observed in this paper a dimensional analysis technique is devised to evaluate quantitatively the magnitude and time of the ensuing large earthquake within the anomalous areas derived from the lurr method based on the theorem two dimensionless quantities associated with the earthquake time and magnitude are derived from five parameters i e the seismic energy e s the average seismic energy e w the maximum value of lurr s seismogenic integral i pp the thickness of seismogenic zone h the time interval from i pp to earthquake t 2 and the shear strain rate dot gamma the statistical relationships between the earthquakes and the two dimensionless quantities are derived by testing the seismic data of the 50 events of m4 5 8 1 occurred in china since 1976 in earthquake prediction the lurr method is used to detect the areas with anomalous high lurr values and then our dimensional analysis technique is applied to assess the optimal critical region magnitude and time of the ensuing event when its seismogenic integral is peaked i pp as study examples we applied this approach to study four large events namely the 2012 m s5 3 hami 2015 m s5 8 alashan 2015 m s8 1 nepal earthquakes and the 2013 songyuan earthquake swam results show that the predicted location time and magnitude correlate well with the actual events this provides evidence that the dimensional analysis technique may be a useful tool to augment current predictive power of the traditional lurr approach

the shikotan earthquake of october 4 1994 lithospheric earthquake a large m w 8 2 earthquake occurred off shikotan is one of the kurile is on october 4 1994 we inverted 32 body wave records to determine the rupture pattern using an iterative deconvolution method the mechanisms of the subevents were allowed to vary during rupture the source parameters obtained are the location of the initial break 43 48 n 147 40 e the centroid depth 56 km strike dip rake 49 75 125 for the total source the seismic moment m o 2 6 10 21 nm m w 8 2 source time duration t 42 s the average rupture velocity 2 5 km s we also determined the mechanism using long period love and rayleigh waves from 14 stations the solution for a finite source distributed over a depth range from 0 to 90 km is strike dip rake 54 76 129 with mo 2 3 10 21 nm in good agreement with that from body waves referring to the extent of the aftershock area and the subevent distribution we estimated the fault area s 120 60 km the average slip d 5 6m and the stress drop 11 mpa we computed synthetic waveforms as well as static displacements using either the steep or the low angle plane as the fault plane and found that the steep dip fault model fits the data better our result the mechanism large centroid depth high stress drop strongly suggests that the 1994 shikotan earthquake is a lithospheric earthquake an intra plate event that ruptures through a substantial part of the subducting oceanic lithosphere this type of lithospheric earthquake is relatively common

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

did the 2008 mw 7 9 wenchuan earthquake trigger the occurrence of the 2017 mw 6 5 jiuzhaigou earthquake in sichuan china

increasing critical sensitivity of the load unload response ratio before large earthquakes with identified stress accumulation pattern the load unload response ratio lurr method is proposed for short to intermediate term earthquake prediction yin x c chen x z song z p yin c 1995 a new approach to earthquake prediction the load unload response ratio lurr theory pure appl geophys 145 701 715 this method is based on measuring the ratio between benioff strains released during the time periods of loading and unloading corresponding to the coulomb failure stress change induced by earth tides on optimally oriented faults according to the method the lurr time series usually climb to an anomalously high peak prior to occurrence of a large earthquake previous studies have indicated that the size of critical seismogenic region selected for lurr measurements has great influence on the evaluation of lurr in this study we replace the circular region usually adopted in lurr practice with an area within which the tectonic stress change would mostly affect the coulomb stress on a potential seismogenic fault of a future event the coulomb stress change before a hypothetical earthquake is calculated based on a simple back slip dislocation model of the event this new algorithm by combining the lurr method with our choice of identified area with increased coulomb stress is devised to improve the sensitivity of lurr to measure criticality of stress accumulation before a large earthquake retrospective tests of this algorithm on four large earthquakes occurred in california over the last two decades show remarkable enhancement of the lurr precursory anomalies for some strong events of lesser magnitudes occurred in the same neighborhoods and during the same time periods significant anomalies are found if circular areas are used and are not found if increased coulomb stress areas are used for lurr data selection the unique feature of this algorithm may provide stronger constraints on forecasts of the size and location of future large events

detection of seamount signatures in seasat altimeter data using matched filters matched filter techniques are described for the detection of characteristic geoid undulation signatures of seamounts in seasat radar altimeter data the technique requires models of the expected undulation signatures and a statistical description of the background seamount free data examples are given of the detection of 11 known seamounts on four distinct tracks further extensions and applications of the matched filter methods are discussed

observed and simulated kinematic properties of loop current rings two rings shed by the loop current in 1980 and 1982 were observed for several months by satellite tracked drifters to migrate across the gulf of mexico the drifter path data have been inverted to obtain estimates of the paths of the centers of the two rings ring shape and the swirl velocities three drifters were deployed in the 1980 ring and the analysis of that data set establishes the variability of the above kinematic estimates for one ring a comparison of the analysis of data from both rings provides some idea on inter ring variability both rings impacted the mexican continental slope at about 22 8 n 95 5 w after a brief adjustment period both rings reestablished and maintained a vortex character for several months in the slope region while migrating slowly to the north the paths of the centers of the two rings along the slope are virtually identical the same analysis routine was applied to some simulated drifter data obtained from the hurlburt and thompson 1980 gulf of mexico primitive equation model in the midgulf the agreement between the observed rings and the simulated ring is good although the former showed stronger interaction with the continental slope topography and or circulation than was seen in the latter along the slope the model ring kinematic characteristics were in extraordinary agreement with the observations

the 1998 papua new guinea earthquake and its fault plane estimated from relocated aftershocks the 1998 papua new guinea earthquake of m w 7 0 occurred near the wewak trench where the north bismarck plate is subducting beneath the australian plate its mechanism is thrust type and one of the nodal planes is almost parallel to the plate interface to determine which of the two nodal planes of the main shock is the fault plane we relocated the main shock and aftershocks using a method of modified joint hypocenter determination we combined and employed two types of data in this study firstly we used data reported by the national earthquake information center neic of the u s geological survey usgs which includes three stations at the northeastern edge of irian jaya and one station in northern papua new guinea from which the epicentral distances are less than 2 degrees secondly in addition to the above permanent station data we used data from temporary aftershock observations near the epicentral area around the sissano lagoon carried out by tsuji et al 1998 using three component seismometers they carried out observations from august 2 to october 2 1998 at three sites although the network did not record the main shock and immediate aftershocks the data obtained by temporary observation sites can clearly assist in identifying their absolute locations since it is possible to apply the joint hypocenter determination jhd method hypocenters were relocated between the coastline and the wewak trench distributed along a nodal plane dipping shallowly to the southwest therefore we can conclude that this nodal plane is the main shock fault and that the 1998 papua new guinea earthquake was an interplate earthquake between the north bismarck and australian plates

verification of geosat altimetry for operational use in the gulf of mexico geosat altimetry is well suited for locating large eddies shed by the loop current in the gulf of mexico we have compared the altimeter data with in situ data obtained during a survey of eddy murphy in june 1988 since there is no significant mean circulation in the central gulf we used the mean sea surface from the first year of altimeter data as a geoid estimate the dynamic height change due to the eddy closely matched the altimeter data although the eddy moved about one third of a degree between the survey and the satellite pass the motion of the eddy was confirmed by the track of an argos buoy

unbending and horizontal fracture of the subducting pacific plate as evidenced by the 1993 kushiro oki and the 1981 and 1987 intermediate depth earthquakes in hokkaido abstract a large number of aftershocks of the 1993 kushiro oki earthquake m jma 7 8 1987 hidaka earthquake m jma 7 0 and 1981 western hidaka earthquake m jma 7 1 have been observed by the seismic network of hokkaido university these three earthquakes are the largest events that have occurred in the depth range from 100 km to 200 km under the pacific side of hokkaido for 109 years they migrated from west to east in the last 12 years their focal mechanism solutions represent typical down dip extension in the lower zone of the double seismic zone in the descending pacific plate we investigated aftershock distributions of the three intermediate depth earthquakes to study physical properties of the descending slab aftershocks of the kushiro oki earthquake spread horizontally over an area of 50 km 40 km a vertical cross section of this aftershock distribution shows that it extends from the lower seismic zone almost to the upper seismic zone it shows a slightly concave shape of about 35 km in length aftershocks of the hidaka and western hidaka earthquakes also extend horizontally over areas of 10 km 10 km and 8 km 12 km respectively these main shocks occurred in the lower seismic zone the horizontal aftershock distributions of all three large earthquakes indicate that the horizontal nodal planes of the focal mechanisms rather than the vertical nodal planes are the fault planes such a characteristic suggests that the descending lithosphere under hokkaido has been unbent macroscopically over the last 12 years unbending and the long horizontal faults of the intermediate depth earthquakes may be caused by mantle flow in the asthenosphere beneath the pacific plate we suggest that the descending slab of about 100 km thickness constitutes two layers a seismic brittle upper layer and an aseismic ductile lower layer small ruptures may tend to occur easily along both boundary surfaces of the upper layer under the action of forces especially unbending and form the double seismic zone

a new statistical test for static stress triggering application to the 1987 superstition hills earthquake sequence over the past several years many investigators have argued that static stress changes caused by large earthquakes influence the spatial and temporal distributions of subsequent regional seismicity with earthquakes occurring preferentially in areas of stress increase and reduced seismicity where stress decreases some workers have developed quantitative methods to test for the existence of such static stress triggering but no firm consensus has yet been reached as to the significance of these effects we have developed a new test for static stress triggering in which we compute the change in coulomb stress on the focal mechanism nodal planes of a set of events spanning the occurrence of a large earthquake we compare the statistical distributions of these stress changes for events before and after the mainshock to decide if we can reject the hypothesis that these distributions are the same such rejection would be evidence for stress triggering we have applied this test to the november 24 1987 elmore ranch superstition hills earthquake sequence and find that those post mainshock events that experienced stress increases of at least 0 01 0 03 mpa 0 1 0 3 bar or that occurred from 1 4 to 2 8 years after the mainshocks are consistent with having been triggered by mainshock generated static stress changes

collinear track altimetry in the gulf of mexico from seasat measurements models and surface truth abstract from 17 september to 10 october 1978 seasat made collinear passes over the gulf of mexico altimeter data for eight three day repeat passes over the eastern gulf were examined using an arc segment fitting technique to determine the mesoscale temporal variability of the sea surface the pattern of sea height variability was then compared with sea height data generated by a numerical model of the gulf hurlburt and thompson 1980 from the simulation of a complete cycle of loop current intrusion and shedding of an anticyclonic eddy the model data was found to match that from the seasat altimeter when an anticyclonic eddy separated from the loop current and the loop began to repenetrate into the eastern gulf analysis of sparse ground truth data from ship of opportunity xbt s satellite infrared imagery of the loop current boundary and synthetic aperture radar sar imagery also from seasat tend to confirm the circulation patterns deduced from the altimeter data and the numerical model author

a detailed subduction structure in the kuril trench deduced from ocean bottom seismographic refraction studies abstract in 1983 we conducted an ocean bottom seismograph obs experiment in the southernmost part of the kuril trench beneath which the pacific plate is subducting under hokkaido island japan the aim of this experiment was to determine crust and upper mantle structure from the oceanic basin to the continental slope by dense seismic refraction profiling using explosives and airguns the total length of the profiles was 560 km along which ten obs s were deployed the observed data were of good quality which enabled us to obtain a detailed velocity structure of the active margin down to 20 30 km we constructed a velocity structure model by ray tracing and amplitude modeling in the oceanic basin the crust has a typical oceanic structure characterized by three layers with p wave velocities of 1 8 3 8 6 5 and 6 5 7 0 km s the velocity gradient in layer 3 increases downward from 0 075 to 0 10 s 1 the moho discontinuity was well constrained by clearly observed p n and p m p phases the total thickness of the oceanic crust was determined to be 8 km and almost constant in the oceanic basin the p wave velocity is 7 9 km s beneath the moho discontinuity which increases downward with a rather small velocity gradient 0 015 0 03 s 1 beneath the continental slope we found relatively low velocity 2 5 to 5 5 5 8 km s material the oceanic moho discontinuity associated with the subducting plate was traced down to a depth of 25 km our seismic data strongly suggest that oceanic layer 2 is smoothly subducting and does not break up to form a wedge structure this result is in remarkable contrast with the velocity structure in the active margin of the ryukyu trench area about 1000 km south of the present experimental area where we found a 12 km thick prominent low velocity wedge is situated 50 150 km landward from the trench axis on the seaward side of the wedge the surface of the igneous basement undulates severely the wedge was probably formed by materials of oceanic origin such a difference in velocity structure suggests that the subduction mechanism in the trench area differs from region to region in the northwestern pacific

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

long term seismic quiescences and great earthquakes in and around the japan subduction zone between 1975 and 2012 an earthquake catalog created by the international seismological center isc was analyzed including 3898 earthquakes located in and around japan between january 1964 and june 2012 shallower than 60 km with the body wave magnitude of 5 0 or larger clustered events such as earthquake swarms and aftershocks were removed from the isc catalog by using a stochastic declustering method based on epidemic type aftershock sequence etas model a detailed analysis of the earthquake catalog using a simple scanning technique zmap shows that the long term seismic quiescences lasting more than 9 years were recognized ten times along the subduction zone in and around japan the three seismic quiescences among them were followed by three great earthquakes the 1994 hokkaido toho oki earthquake m w 8 3 the 2003 tokachi oki earthquake m w 8 3 and the 2011 tohoku earthquake m w 9 0 the remaining seven seismic quiescences were followed by no earthquake with the seismic moment m 0 3 0 1021 nm m w 8 25 which are candidates of the false alarm the 2006 kurile islands earthquake m w 8 3 was not preceded by the significant seismic quiescence which is a case of the surprise occurrence as a result when limited to earthquakes with the seismic moment of m 0 3 0 9 1021 nm four earthquakes occurred between 1976 and 2012 in and around japan and three of them were preceded by the long term seismic quiescence lasting more than 9 years

high resolution mapping of tec perturbations with the gsi gps network over japan two dimensional total electron content tec perturbations over japan are mapped with the geographical survey institute gsi gps network geonet gps earth observation network its spatial resolution is 0 15 latitude 0 15 longitude and temporal resolution is 30 seconds two dimensional tec observations with these high resolutions revealed spatial structures and temporal evolutions of traveling ionospheric disturbances tids in the nighttime mid latitude ionosphere on july 03 1997 a preliminary result of the tec perturbation mapping indicates that it would be a strong tool to investigate the ionospheric structures in detail coordinated observations with other ionospheric observation techniques such as incoherent scatter is radars airglow imagers and ionosondes are needed to clarify the vertical structure of the ionosphere

two mode long distance propagation of coseismic ionosphere disturbances 1 using gps total electron content tec measurements we analyzed ionosphere response to the great kurile earthquake of 4 october 1994 high spatial resolution of the japanese dense array of gps receivers geonet provided us the unique opportunity to observe the evolution of coseismic ionospheric disturbances cid which propagated for more than 1800 km away from the epicenter plotting a traveltime diagram for the cid and using an array processing technique within the approximation of a spherical cid wavefront we observed a phenomenon of cid separation into two modes and we found that characteristics of the cid depend on the distance from the epicenter the maximum of the cid amplitude was observed at 500 km from the epicenter within the first 600 700 km the cid propagation velocity was about 1 km s which is equal to the sound speed at the height of the ionospheric f layer starting from 600 to 700 km out from the epicenter the disturbance seems to divide into two separate perturbations with each propagating at a different velocity about 3 km s for the one and about 600 m s for the other apparently the tec response in the far field of the cid source is a mixture of signals that further splits into two modes because of the difference in their velocities our observations are in good agreement with the results of space time data processing in the approximation of a spherical wavefront of cid propagation

the central italy seismic sequence 2016 spatial patterns and dynamic fingerprints the paper investigates spatio temporal aspects of the seismic sequence that started in central italy amatrice lazio region in august 2016 causing hundreds of fatalities and producing major damage to settlements on one hand scaling properties of the landscape topography are identified and related to geomorphological processes supporting the identification of preferential spatial directions in tectonic activity and confirming the role of the past tectonic periods and ongoing processes with respect to the driving of the geomorphological evolution of the area on the other hand relations between the spatio temporal evolution of the sequence and the seismogenic fault systems are studied the dynamic fingerprints of seismicity are established with the help of events thread analysis eta which characterizes anisotropy in spatio temporal earthquake patterns eta confirms the fact that the direction of the seismogenic normal fault oriented n nw s se is characterized by persistent seismic activity more importantly it also highlights the role of the pre existing compressive structures neogenic thrust and transpressive regional fronts with a trend oriented n ne s sw in the stress transfer both the fractal features of the topographic surface and the dynamic fingerprint of the recent seismic sequence point to the hypothesis of an active interaction between the quaternary fault systems and the pre existing compressional structures

tikhonov s regularization for deconvolution in the empirical green function method and vertical directivity effect abstract application of tikhonov s technique using input errors for the parameter of regularization estimation enhances the accuracy and stability of the reconstruction of a source time function stf by the empirical green function egf method that gives us an opportunity to use simultaneously for analysis body and surface waves data and to estimate the horizontal and vertical directivity effects knowledge of the last is particularly useful for the choice of an active nodal plane of earthquakes with the dip slip fault orientation that allows us to classify these earthquakes to the interplate or intraplate types and thereby to reach the better understanding of tectonic processes in the region of interest by way of illustration an attempt to estimate average parameters of faulting in a first approximation is made herein for two russian far east large events with opposite types of focal mechanism orientation strike slip and dip slip the former is not a matter of interest in the context of vertical directivity effect but enables us to test the method the directivity analysis of pulse durations and inverse amplitudes of the relative source time functions rstfs restored at eight globally distributed stations iris indicates that the destruction in the source of the neftegorsk earthquake 05 27 1995 m w 7 1 propagated roughly horizontally in the direction 8 11 during 19 2 0 4 s along the rupture extending 35 5 4 9 km the calculated slip distribution along the rupture coincides within the error with the results of field geological measurements on the causal surface fault that proves that the neftegorsk earthquake source is well described by the model of the linear unilateral fault and gives a good assessment of the method applied the average parameters of faulting in the kamchatka earthquake 03 08 1999 m w 6 9 have been determined from data of 13 station iris it was shown that the destruction in its source propagated downward at an angle of about 60 with horizon in the direction about s156 e during 13 4 0 2 s along the rupture totaling 25 5 2 3 km in length therefore the nodal plane steeply dipped to the se was active and this event can be regarded as an intraplate type two asperities can be selected the first with the maximum slip 3 3 m located at a distance of about 7 km from the onset of rupture and the second with the maximum slip about 0 9 m centered at approximately 19 km from that

oceanographic and geophysical applications of satellite altimetry since the last quadrennial report new satellite altimeter data have not been generally available nevertheless important progress has been made from analyses of geos 3 and seasat data the marine gravity field has been determined to an extraordinary resolution and accuracy and important solid earth geophysical interpretations made in the area of oceanography statistical estimates of the variability of dynamic topography have been published methods for incorporating altimeter data into numerical models have been developed and applied and tentative but interesting determinations of the mean circulation have been made in addition altimeter waveform analysis has made it possible to use altimeter data to determine elevations of major ice fields finally important new insights into the nature of satellite ephemeris error and its influence on altimetrically derived sea surface topography have been achieved

state of stress from focal mechanisms before and after the 1992 landers earthquake sequence the state of stress in the eastern california shear zone ecsz changed significantly because of the occurrence of the 1992 m w 6 1 joshua tree and the m w 7 3 landers earthquakes to quantify this change focal mechanisms from the 1975 galway lake sequence the 1979 homestead valley sequence background seismicity from 1981 to 1991 and the 1992 landers sequence are inverted for the state of stress in all cases the intermediate principal stress axis s2 remained vertical and changes in the state of stress consisted of variations in the trend of maximum and minimum principal stress axes s 1 and s 3 and small variations in the value of the relative stress magnitudes in general the stress state in the ecsz has s 1 trending east of north and 0 43 to 0 65 suggesting that the ecsz is a moderate stress refractor and the style of faulting is transtensional south of the pinto mountain fault in the region of the 1992 joshua tree earthquake the stress state determined from the 1981 to 1991 background seismicity changed on 23 april and again on 28 june 1992 in the central zone s 1 rotated from n14 5 e to n28 5 e on 23 april and back again to n16 5 e on 28 june thus the landers mainshock in effect recharged some of the shear stress in the region of the m w 6 1 joshua tree earthquake comparison of the state of stress before and after 28 june 1992 along the landers mainshock rupture zone showed that the mainshock changed the stress orientation the s1 trend rotated 7 to 20 clockwise and became progressively more fault normal from south to north along the emerson camp rock faults the variation was so prominent that the focal mechanisms of aftershocks could not be fit by a single deviatoric stress tensor the complex distribution of p and t axes suggests that most of the uniform component of the applied shear stress along the northern part of the rupture zone was released in the mainshock the san bernardino mountains region of the m w 6 2 big bear earthquake has a distinctively different state of stress as compared to the landers region with s 1 trending n3 5 w this region did not show any significant change in the state of stress following the 1992 m w 6 2 big bear sequence

the sensitivity of the loa unload response ratio and critical region selection before large earthquakes occurrence of a large earthquake could be predicted by anomalous temporal increase of the load unload response ratio lurr previous studies have indicated that the stress field that existed before a large earthquake may have a strong influence on the evaluation of lurr in this paper we replace the circular region usually adopted in lurr practice with an area within which the tectonic stress change would mostly affect the coulomb stress on a potential seismogenic fault of a future event this algorithm is devised to increase the sensitivity of lurr to measure criticality of stress accumulation before a large earthquake in the algorithm we assess the stress change and identify the areas with increased coulomb stress before an earthquake using a simple back slip dislocation model of the event retrospective tests of this algorithm on some disastrous earthquakes that occurred in the chinese mainland in recent years show remarkable enhancement of the lurr precursory anomalies by using the hypothetical faults for the large earthquake prediction we further illustrate that the new algorithm is more sensitive to detect future earthquake of a particular magnitude range and location than the circular region algorithm hence where sufficient information of the regional fault tectonics is given the coulomb stress algorithm can be used to augment current lurr technique for seismic hazard estimation

space geodetic observation of deep basal subduction erosion in northeastern japan abstract observation of tectonic erosion von huene and scholl rev geophys 29 1991 279 316 in a subduction zone has been difficult as it leaves little geological and geophysical evidence three dimensional velocity profiles of crustal movement obtained by global positioning system across ne and sw japan agree well with those predicted by the elastic loading of the subducting slabs however vertical velocities in the ne japan forearc show significant negative deviation relative subsidence this may indicate loss of material at the plate interface that can be attributed to the erosion of the upper plate by the underthrusting slab basal subduction erosion the estimated rate 15 mm yr down to a slab depth of 90 km is somewhat faster than the geological average the erosion speed may be variable being controlled by the surface roughness of subducting slabs

source models of two large intraslab earthquakes from broadband strong ground motions we construct source models of two large intraslab earthquakes the 1993 kushiro oki and 1994 hokkaido toho oki earthquakes along the southern kurile hokkaido arc based on strong motion records the source models well explain observed broadband strong ground motions we assume a distribution of rectangular shaped asperities on a fault plane and apply the empirical green9s function method to the synthesis of strong ground motions from the asperities the asperity parameters area and stress drop are estimated by matching the synthetic waveforms displacement velocity and acceleration time histories and spectra to the observed ones our source models have the following characteristics compared with those of inland and plate boundary earthquakes having a comparable seismic moment 1 the total asperity area is much smaller and 2 the stress drop is extremely high about 200 400 mpa these indicate that the large intraslab earthquakes radiate seismic energies from a small area in a short time this rupture process results in extremely strong radiation of short period seismic waves finally we confirm a correlation between outer entire fault size seismic moment and short period level of the acceleration source spectrum and inner fault parameters areas and stress drops of asperities for the two intraslab earthquakes

global positioning system network analysis with phase ambiguity resolution applied to crustal deformation studies in california a 5 year campaign is in progress in central and southern california to monitor tectonic motions using observations of the global positioning system gps satellites evidence from geological and space geodetic data indicates that significant horizontal deformations of order 10 mm yr are occurring west of the san andreas fault along the california margin we demonstrate using data from initial epoch measurements in january 1987 that the goal of measuring horizontal deformations with an accuracy of 5 mm yr over the duration of the campaign should be readily achievable the gps network was designed to span a wide range of baseline lengths within california and across north america to aid in phase ambiguity resolution an important factor in achieving highest accuracy baseline determinations we present an efficient algorithm for multisession network analysis of gps data with simultaneous orbit determination and ambiguity resolution using this algorithm with the california data we demonstrate the improvement obtained in station position and satellite orbit estimation when the phase ambiguities are resolved we demonstrate several millimeters 1 part in 108 short term repeatability over five single session daily analyses for horizontal baseline components and length and several tens of millimeters for the vertical comparison with the independently determined very long baseline interferometry baseline between mojave and owens valley suggests that the accuracy is at the same level as the repeatability we show that simultaneous multisession analyses with ambiguity resolution improve the baseline and satellite orbit estimates compared to the single session analyses with the single session analyses we were able to resolve all phase ambiguities on baselines within california with the multisession analyses we were able to resolve the phase ambiguities for most of the network over regional and continental scales

where and why do large shallow intraslab earthquakes occur we try to find how often and in what regions large earthquakes m 7 0 occur within the shallow portion 20 60 km depth of a subducting slab searching for events in published individual studies and the harvard university centroid moment tensor catalogue we find twenty such events in e hokkaido kyushu sw japan s mariana manila sumatra vanuatu n chile c peru el salvador mexico n cascadia and alaska slab stresses revealed from the mechanism solutions of these large intraslab events and nearby smaller events are almost always down dip tensional except for e hokkaido manila and sumatra the upper plate shows horizontal stress gradient in the arc perpendicular direction we infer that shear tractions are operating at the base of the upper plate in this direction to produce the observed gradient and compression in the outer fore arc balancing the down dip tensional stress of the slab this tectonic situation in the subduction zone might be realized as part of the convection system with some conditions as shown by previous numerical simulations 2003 elsevier b v all rights reserved

the 1995 off etorofu earthquake joint relocation of foreshocks the mainshock and aftershocks and implications for the earthquake nucleation process abstract prominent foreshock activity preceded the mw 7 9 off etorofu earthquake in the kurile islands on 3 december 1995 using a modified joint hypocenter determination method hurukawa 1995 we simultaneously relocated foreshocks the mainshock and aftershocks to study the foreshock activity in detail in view of the nucleation process of a large earthquake the distribution of relocated earthquakes and their focal mechanisms suggest that the 1995 off etorofu earthquake was an interplate earthquake at the boundary between the north american and pacific plates its source area overlaps with those of the 1958 off etorofu mw 8 3 and the 1963 off urup mw 8 5 earthquakes nine days before the occurrence of the mainshock a first immediate foreshock of magnitude 6 4 occurred at the deepest point of the foreshock area this event was followed by many foreshocks including three additional m 6 events which occurred east and southeast of the first foreshock the foreshock area expanded toward the trench axis with a velocity of several to several tens centimeters per second the number of events per day increased daily and the final size of the foreshock area was about 80 30 km eventually the rupture of the mainshock started at the deepest point of the foreshock area these observational facts are consistent with recent theoretical studies and laboratory experiments in which foreshocks are regarded as the rupture of localized asperities in a broad weak zone where the nucleation of the large earthquake started

the geodetic signature of the m8 0 oct 9 1995 jalisco subduction earthquake the october 1995 mw 8 0 jalisco subduction earthquake has provided a thorough geodetic observation of the coseismic subduction process an 11 station regional gps network located directly onshore of the rupture demonstrates consistent vertical subsidence verified by tide gauge data and southwest directed extension with measured displacements reaching 1 meter unusually shallow and non uniform faulting is required to explain the displacements we determine that up to 5 meters of slip occurred within the upper 15 km of the thrust fault zone and 2 meters possibly as shallow as 8 km and that slip was likely distributed in two main patches the paucity of continental sediments in this subduction zone could be responsible for the anomalously shallow faulting

a ship and satellite view of hydrographic features in the western gulf of mexico in april 1980 nearly synoptic hydrographic observations were obtained in the western gulf of mexico by satellite and ship a meandering surface thermal front which turned northeastward from the mexican coast near 23 sup 0 n was prominent in the satellite infrared observations the front separated a southern anticyclone and a northern cyclone both of which had horizontal scales of several 100 km and were prominent in the subsuface hydrographic observations the eastward geostrophic volume transport in the confluent leg of the two features was roughly equal to that of the florida current a shallow layer of fresh cool water from the texas shelf region extended approx 300 km seaward into the cyclone along the northern side of the front remnant subtropical underwater in the core of the april anticyclone indicates its origin in the eastern gulf loop current

determining the ocean circulation and improving the geoid from satellite altimetry abstract the combined problem of determining the ocean circulation and improving the geoid from satellite altimetry is formulated and studied minimum variance estimation is used to form optimum estimates of the ocean topography and the geoid these estimates are a function of the altimeter observations prior knowledge of the ocean circulation and prior knowledge of the geoid particular emphasis is placed on the use of a dynamical ocean model as a source of a priori oceanographic information capable of discriminating between geoid errors and ocean topography the technique is illustrated in a simulation study of gulf stream variability in which an ocean topography degraded by noise representing the uncertainty in a gravimetric geoid is reconstructed by assimilation into an ocean model at the same time an improved estimate of the geoid is made

absolute far field displacements from the 28 june 1992 landers earthquake sequence on 28 june 1992 the largest earthquake in california in 40 years surface wave magnitude ms 7 5 occurred near the small town of landers in southeastern california and was followed three hours later by the nearby ms 6 5 big bear earthquake1 fortuitously the landers earthquake sequence coincided with the first week of the official three month test period of the international global positioning system and geodynamics service2 igs giving us an unprecendented opportunity to detect absolute pre co and post seismic displacements at a distance of 50 200 km from the main rupture with millimetre level precision mutual and independent confirmation of some of our geodetic results are demonstrated by bock et al in this issue3 for the landers earthquake the observed displacements indicate that the depth of the bottom of the rupture is shallower towards the northern end displacements were dominantly symmetric and the rupture extended further south on the johnson valley fault than has been mapped on the basis of surface ground offsets the combined geodetic moment for the landers and big bear earthquakes 1 1 1020 n m 1 agrees well with teleseismic estimates

coseismic crustal deformation from the 1994 hokkaido toho oki earthquake monitored by a nationwide continuous gps array in japan using a brand new nationwide continuous gps array we monitored coseismic displacements from the october 4 1994 hokkaido toho oki kurile islands earthquake mjma 8 1 based on 2 week time series of site coordinates of 21 gps stations we present a coseismic deformation field of whole hokkaido within 1 cm precision for example the station at nemuro 170 km west of the epicenter moved 44 cm to the east and subsided 10 cm even stations in southern hokkaido 600 km apart from the epicenter moved a few cm horizontally toward the epicenter we compare the gps result with displacements calculated from two preliminary models assuming fault planes parallel or perpendicular to the kurile trench since the observed were far field displacements on land both models can explain the gps result

lagrangian observations of an anticyclonic ring in the western gulf of mexico this analysis documents for the first time the movement and velocity characteristics of an anticyclonic ring the ring was pinched off from the loop current in the fall of 1980 and moved into the western gulf of mexico lagrangian measurements obtained from satellite tracked drifters show that typical speeds of the near surface currents associated with this ring are about 50 cm s there is also a surprising amount of higher frequency current fluctuations these include diurnal and semidiurnal tides a basin tidal resonance and a free gravity mode

sampling strategies and model assimilation of altimetric data for ocean monitoring and prediction numerical forecasts using simulated altimeter data are generated in order to examine the assimilation of altimeter derived sea surface heights into numerical ocean circulation models a one layer reduced gravity primitive equation circulation model of the gulf of mexico is utilized the gulf of mexico is chosen because of its amenability to modeling and the ability of low vertical mode models to reproduce many of the observed dynamical features of gulf circulation the simulated data are obtained by flying a hypothetical altimeter over the model ocean and sampling the model sea surface in a manner similar to a real altimeter the data are used to examine spatial sampling requirements for accurate resolution of oceanic eddies and in forecast mode the assimilation of asynoptic altimeter data into numerical models results indicate that for a stationary circular eddy approximately two tracks either ascending or descending across the eddy are sufficient to ensure adequate spatial resolution an irregularly shaped eddy may require three or four tracks in addition the study reveals that if the track spacing is sufficient to resolve the height field of an eddy the along track geostrophic velocity component is determined with equivalent accuracy to that of the cross track component simulated gulf of mexico circulation forecasts suggest that the numerical model can effectively assimilate asynoptic altimeter measurements optimum sampling strategies for a single beam altimeter and intermittent updating of the nowcast forecast are examined

new discoveries in dynamics of an m8 earthquake phenomena and their implications from the 2003 tokachi oki earthquake using a long term monitoring cabled observatory at the 2003 tokachi oki earthquake of m8 seafloor phenomena such as a generation process of tsunami seafloor uplifts turbidity current etc were observed using a cabled observatory installed on the seafloor the turbidity current was observed as a benthic storm caused presumably by the mainshock the seafloor uplifts were observed at the mainshock and continuously after the mainshock the uplifts were 0 35 0 37 and 0 12 m for epicentral distances of 25 5 31 4 and 81 7 km respectively after the mainshock a continuous uplift of the seafloor is observed at all three pressure gauge locations indicating that there was a change in the state of friction on the plate boundary interface by the mainshock in this paper we first show what was observed using the cabled observatory installed right above the focal area of the earthquake and then we discuss to summarize these phenomena associated with the earthquake its possible causes and future directions in long term monitoring of seismogenic processes

development of a new approach to earthquake prediction load unload response ratio lurr theory the seismogenic process is nonlinear and irreversible so that the response to loading is different from unloading this difference reflects the damage of a loaded material based on this insight a new parameter load unload response ratio lurr was proposed to measure quantitatively the proximity to rock failure and earthquake more than ten years ago in the present paper we review the fundamental concept of lurr the validation of lurr with experimental and numerical simulation the retrospective examination of lurr with new cases in different tectonic settings california usa and kanto region japan the statistics of earthquake prediction in terms of lurr theory and the random distribution of lurr under poisson s model finally we discuss lurr as a parameter to judge the closeness degree to soc state of the system and the measurement of tidal triggering earthquake the load unload response ratio lurr theory was first proposed in 1984 yin 1987 subsequently a series of advances were made yin and dyin 1991 yin 1993 yin et al 1994a b 1995 maruyama 1995 in this paper the new results after 1995 are summarized yin et al 1996 wang et al 1998a zhuang and yin 1999

cyclonic eddies in the eastern gulf of mexico abstract cold domed cyclonic eddies juxtaposed to the cyclonic shear side of the gulf loop current are observed in simultaneously obtained hydrographic current meter mooring and satellite infrared data the cyclones are initially observed in the satellite data as cold perturbations on the northern extreme of the current and grow either into a cold tongue or a quasi stable meander off the dry tortugas florida areal shipboard surveys show closed isopleths of temperature and salinity and surface geostrophic current speeds relative to 1000 db are in excess of 100 cm s 1 the diameter of the cold domes varied from 80 to 120 km separation of large anticyclonic rings is always observed to be preceded by cyclonic eddies in the transition zone between campeche bank and the west florida shelf but only on the eastern side not every cyclonic eddy off dry tortups is associated with the separation of an anticyclonic ring some are eroded away by the florida current but they have never been observed in 10 years

earthquake distribution in the subduction zone off eastern hokkaido japan deduced from ocean bottom seismographic and land observations summary in 1986 observations of microearthquakes were conducted with the use of five ocean bottom seismometers obss on the continental slope east of the kushiro submarine canyon ksc off hokkaido island japan the observation area is located about 50 100 km landward of the southern kuril trench beneath which the pacific plate is subducted toward hokkaido island the obs data were analysed together with land data on hokkaido island to determine the precise earthquake distribution and the geometry of the subducted plate the obs data revealed for the first time the seaward seismicity east of ksc high and shallow seismicity is concentrated in an area between the coast line of hokkaido island and the 2000 m isobath a region between the 2000 and 4000 m isobaths corresponds to the source area of an interplate earthquake occurring in 1973 the nemuro hanto oki earthquake m 7 4 the obs array detected more than 10 events in this region most of them however are classified as earthquakes occurring within the subducted plate and the remarkable aftershock activity of the 1973 event is not recognized the seismic activity is extremely low between the 4000 and 6000 m isobaths as is commonly seen in subduction zones the seismicity is also very low beneath the trench in contrast with the adjacent trench areas in a vertical section taken perpendicular to the trench axis most of the located events form a seismic plane dipping landward the dip angle of the plane is 20d 25d beneath the continental slope while 35d 40d under hokkaido island the change in dip angle occurs 150 km landward of the trench axis this seismic plane is located 30 40 km below the plate boundary defined from the aftershock distribution of the nemuro hanto oki event the seismicity on the plate boundary is correlated with the geometry of the subducted plate the high activity occurs in a restricted region where the subducted plate shows a remarkable bend the seismic activity obtained is different from those in the adjacent regions along the southern kuril trench in particular the regional difference in seismicity is remarkable between the western and eastern sides of ksc our result suggests that the subduction zone along the kuril trench is divided into several tectonic blocks and ksc is one of their boundaries

altimeter data and geoid error in mesoscale ocean prediction some results from a primitive equation model a primitive equation ocean model has been applied to the study of mesoscale ocean dynamics and prediction using sea surface height information derived from a satellite borne altimeter results from a model of the gulf of mexico were directly compared with the altimeter data from geos 3 and seasat reported by marsh et al 1984 and in situ hydrographic data analyzed by maul and herman 1985 in the eastern gulf the amplitude and position of relative maxima of sea surface height variability were found to be similar for model altimeter and in situ data in the central gulf the model and the altimeter derived sea surface height variability maps were similar but differed considerably from the in situ results the mean sea surface in the model and from the in situ data also agreed well in the eastern gulf but there was little agreement in the central gulf while there is no geoid adequate for determining an independent altimetric estimate of the mean dynamic height of the sea surface in the gulf by differencing the geoid with the altimeter derived mean sea surface the model dynamic mean sea surface can be subtracted from the mean surface of marsh et al 1984 to obtain a new estimate of the gulf geoid which may be the best geoid available in that region for several years a benchmark experiment truth was integrated to statistical equilibrium and compared with results from four experiments in which the model was initialized with fields modified from archived benchmark data the experiments differed only in the initialization fields each experiment was integrated for 100 days with inflow transport remaining constant throughout the integration the idealized experiments were initialized geostrophically 1 with the exact sea surface and pycnocline height fields 2 with only the exact sea surface heights and a pycnocline assumed to compensate it such that the deep pressure perturbations vanished 3 just as in case 2 but with a geoid error component added on small spatial scales and 4 just as in case 3 except the geoid error model included an additional contribution in strong geoid gradient regions the sequence of four numerical experiments showed that 1 geostrophic initialization with exact sea surface and pycnocline height information provided accurate forecasts to 100 days 2 even when only the sea surface height information was provided to the numerical model for geostrophic initialization and deep pressure perturbations assumed to vanish at the initial time the forecasts were superior to persistence or climatology over the 100 day forecast period and 3 errors in the geoid on spatial scales comparable to the grid resolution of the model did not seriously degrade the forecast even in dynamically active regions with large gradients in the geoid height where instability processes were observed to occur

on the circulation of the western gulf of mexico with observations from april 1978 in april 1978 the circulation pattern in the western gulf of mexico was dominated by a cyclonic circulation feature centered near 25 20 n 95 20 w and an anticyclonic circulation feature centered near 23 30 n 95 50 w the north south scales of both gyres are approximately 225 km while the east west scales are greater than 450 km an eastward geostrophic transport of 29 7 106 m3 s is found between the centers of the cyclone and the anticyclone we believe that both the anticyclone and the cyclone migrated to the western gulf from the loop current region of the eastern gulf the anticyclone is probably supplemented by a wind driven circulation as described by blaha and sturges and an eastward extension of the wind driven current which flows to the south along the lower texas shelf may intensify the cyclone and or anticyclone also this extension of the texas shelf current may tend to confine the anticyclone to the south and the cyclone to the north of the current s location

source depth dependence of micro tsunamis recorded with ocean bottom pressure gauges the january 28 2000 mw 6 8 earthquake off nemuro peninsula japan abstract micro tsunami waves with a maximum amplitude of 4 6 mm were detected with the ocean bottom pressure gauges on a cabled deep seafloor observatory south of hokkaido japan following the january 28 2000 earthquake m w 6 8 in the southern kuril subduction zone we model the observed micro tsunami and estimate the focal depth and other source parameters such as fault length and amount of slip using grid searching with the least squares method the source depth and stress drop for the january 2000 earthquake are estimated to be 50 km and 7 mpa respectively with possible ranges of 45 55 km and 4 13 mpa focal depth of typical inter plate earthquakes in this region ranges from 10 to 20 km and stress drop of inter plate earthquakes generally is around 3 mpa the source depth and stress drop estimates suggest that the earthquake was an intra slab event in the subducting pacific plate rather than an inter plate event in addition for a prescribed fault width of 30 km the fault length is estimated to be 15 km with possible ranges of 10 20 km which is the same as the previously determined aftershock distribution the corresponding estimate for seismic moment is 2 7 10 19 nm with possible ranges of 2 3 10 19 3 2 10 19 nm standard tide gauges along the nearby coast did not record any tsunami signal high precision ocean bottom pressure measurements offshore thus make it possible to determine fault parameters of moderate sized earthquakes in subduction zones using open ocean tsunami waveforms

a five years super slow aseismic precursor model for the 1994 m8 3 hokkaido toho oki lithospheric earthquake based on tide gauge data 1 here we present a super slow aseismic event model prior to the magnitude 8 3 kurile island hokkaido toho oki earthquake on 4 october 1994 based on data recorded by two tide gauges located 50 150 km from the earthquake epicenter both instruments recorded several cm of subsidence during a five year period prior to the earthquake the observed signals are consistent with a precursory quasi stable slip on the western half of the hokkaido toho oki fault plane when recognized such aseismic events can considerably improve our intermediate term several years prediction capability

crustal stress field in southern california and its implications for fault mechanics we present a new high spatial resolution image of stress orientation in southern california based on the inversion of earthquake focal mechanisms we use this image to study the mechanics of faulting in the plate boundary region the stress field contains significant spatial heterogeneity which in some cases appears to be a result of the complexity of faulting and in other cases appears to be a cause temporal changes in the stress field are also observed primarily related to major earthquakes the observed 15 10 rotation of the stress axes due to the 1992 m7 3 landers mainshock implies that the deviatoric stress magnitude in the crust is low of the order of 10 mpa this suggests that active faults in southern california are weak the maximum principal stress axis near the san andreas fault is often at 50 to the fault strike indicating that the shear stress on the fault is comparable to the deviatoric stress the san andreas in southern california may therefore be a weak fault in a low strength crust

subducting oceanic crusts of the philippine sea and pacific plates and weak zone normal compression in the kanto district japan summary oceanic crusts subducting into the mantle were detected by analyses of mantle earthquakes in the kanto district central japan earthquakes in a depth range of 30 80 km in the southwestern ibaraki prefecture were relocated by a modified method of joint hypocentre determination we obtained a good distribution map of hypocentres and focal mechanisms a boundary layer between the eurasian and philippine sea plates was found where thrust earthquakes with p axes in the nw se direction and of which low angle nodal planes dip northward occurred in a layer with a thickness of about 4 km the p wave velocity in this layer is estimated to be less than about 7 0kms l another boundary layer between the philippine sea and pacific plates exists about 15 km beneath the above boundary layer thrust earthquakes with p axes in the ew direction and of which low angle nodal planes dip westward occurred in this layer that also has a thickness of about 4km furthermore normal faulting earthquakes of which the p axes are almost perpendicular to the boundary layers were found immediately outside the boundary layers combining these results we can conclude that the boundary layers are oceanic crusts that exist at the top of the subducting philippine sea and pacific plates weak zone normal compression was proposed to result from the existence of low velocity oceanic crusts at plate boundaries this hypothesis can be explained because only stress caused by relative motion of the two plates is consumed inside the weak oceanic crust the remnant stress after subtracting the above stress from the tectonic one applied at the plate boundary is the stress of which the p axis is normal to the plate boundary

temporal and spatial evolution of load unload response ratio before the m7 0 jiuzhaigou earthquake of aug 8 2017 in sichuan province the load unload response ratio lurr method has been proposed to evaluate earthquake potential this method can be used to investigate the regional stress strain field change and fault instability associated with the preparation of a large earthquake in this study we explore the temporal and spatial evolution of the lurr anomalies before the m7 0 jiuzhaigou earthquake that occurred on aug 8 2017 in sichuan province we calculate the lurr values by using benioff strain of the small earthquakes within 100 200 300 and 500 km from the epicenter and 12 years prior to the main shock the loading and unloading phases are determined by calculating the change of coulomb failure stress caused by earth tide in the tectonically preferred slip direction on the fault surface of the major event results show that the lurr values remain at a low level for years until 2014 when the lurr values increase to an anomalously high level meanwhile the magnitude of the anomalies decrease with the distance from the epicenter and can hardly be observed within the 500 km radius combining with the spatial distribution of the lurr we find that the development of anomalies before the mainshock can be divided into two stages during the periods of 2014 2015 the significant anomalies were observed in the epicenter and its northwest region and then in 2016 the anomalies were detected in the southeast area of the earthquake which expanded around the huya fault and finally reached the epicenter months before the mainshock the earthquake is located at the intersection area of lurr anomalies of the two time periods suggesting the generation of the jiuzhaigou earthquake

locating small aftershocks using a small aperture temporary seismic array in this paper we developed a specialized method to locate small aftershocks using a small aperture temporary seismic array the array location technique uses the first p arrival times to determine the horizontal slowness vector of the incoming p wave then combines it with s p times to determine the event location in order to reduce the influence of lateral velocity variation on the location determinations we generated slowness corrections using events well located by the permanent broadband network as calibration events then we applied the corrections to the estimated slownesses applications of slowness corrections significantly improved event locations this method can be a useful tool to locate events recorded by temporary fault zone arrays in the near field but unlocated by the regional permanent seismic network as a test we first applied this method to 64 well located aftershocks of the 1992 landers california earthquake recorded by both the caltech usgs southern california seismic network and a small aperture temporary seismic array the average horizontal and vertical separations between our locations and the well determined catalogue locations are 1 35 and 1 75 km respectively we then applied this method to 132 unlocated aftershocks recorded only by the temporary seismic array the locations show a clear tendency to follow the surface traces of the mainshock rupture

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

the 2000 nemuro hanto oki earthquake off eastern hokkaido japan and the high intraslab seismic activity in the southwestern kuril trench 1 the 2000 nemuro hanto oki earthquake mw6 8 occurred in the southwestern part of the kuril trench the hypocenter was located close to the aftershock region of the great 1994 kuril earthquake mw8 3 named the 1994 hokkaido toho oki earthquake by the japan meteorological agency for which the fault plane is still in debate analysis of the 2000 event provides a clue to resolve the fault plane issue for the 1994 event the hypocenters of the 2000 main shock and aftershocks are determined using arrival times from a combination of nearby inland and submarine seismic networks with an improved azimuthal coverage they clearly show that the 2000 event was an intraslab event occurring on a shallow dipping fault plane between 55 and 65 km in depth the well focused aftershock distribution of the 2000 event the relative location of the 1994 event with respect to the 2000 event and the similarity between their focal mechanisms strongly suggest that the faulting of the great 1994 earthquake also occurred on a shallow dipping fault plane in the subducting slab the recent hypocenter distribution around the 1994 aftershock region also supports this result large intraslab earthquakes occurring to the southeast of hokkaido may occur due to a strong coupling on the plate boundary which generates relatively large stress field within the subducting pacific plate

quick aftershock relocation of the 1994 shikotan earthquake and its fault planes the 1994 shikotan earthquake of mw 8 2 occurred near the western kurile trench where the pacific plate is subducting beneath the north american plate although its mechanism is thrust type it is not a typical low angle thrust event with a nodal plane parallel to the plate boundary that occurs at the plate boundary in order to determine which of the two nodal planes of the main shock was the fault plane we relocated the main shock and all aftershocks with m 5 3 using a modified joint hypocenter determination method earthquakes on the northwestern side of the aftershock area including the main shock are located along a plane dipping east southeastward with a dip of 70 this plane is about 80 to 150 km long and 70 km wide the main shock occurred at the north northeastern bottom of this plane which is almost parallel to one of the two nodal planes of the main shock determined by harvard university which has a strike of n51 e and a dip of 76 thus we conclude that this plane is the fault plane that the fault broke at the northeastern bottom of the fault plane and that the rupture propagated to the surface and also to the southeast in addition to the aftershocks aligned with this fault plane there is a secondary alignment which is subparallel to the main fault plane and about 50 km east where the largest aftershock of mw 7 3 occurred on oct 9 since several aftershocks occurred on this secondary fault plane on the same day as the main shock it seems reasonable to suppose that this secondary fault plane was generated together with the main fault plane at the time of the main shock

two seismic gaps on the sagaing fault myanmar derived from relocation of historical earthquakes since 1918 1 relocation of six m magnitude 7 0 earthquakes near the sagaing fault in myanmar since 1918 allows us to image earthquake history along the sagaing fault all the earthquakes were relocated on the sagaing fault by using the modified joint hypocenter determination method combining the relocated epicenters with information on foreshocks aftershocks seismic intensities and coseismic displacement we estimated the location of the fault plane that ruptured during each earthquake this analysis revealed two seismic gaps one between 19 2 n and 21 5 n in central myanmar and another south of 16 6 n in the andaman sea considering the length of the first seismic gap 260 km a future earthquake of up to m 7 9 is expected to occur in central myanmar because nay pyi taw the recently established capital of myanmar is located on the expected fault its large population is exposed to a significant earthquake hazard

genesis of a gulf of mexico ring as determined from kinematic analyses the kinematics of the loop current are studied using trajectories of drifters in the gulf of mexico during mid june through september 1985 one of the drifters was in the loop current proper while other drifters were in two recently shed loop current rings the drifter in the loop current showed strong anticyclonic motion during the study period this loop current anticyclone first began off the northwest coast of cuba it rapidly moved northward into the gulf of mexico as a ring pinched off from the loop current analysis of the loop current drifter motion showed that the anticyclone became an integral part of the loop current taking on many of the characteristics of the most recently shed ring the results of the analysis suggest a process by which loop current rings can be generated apparently this mechanism can cause the loop current to become reconfigured in 2 3 months for beginning the process of ring separation

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

interpretation of the 1993 2001 and 2002 guam earthquakes as intraslab events by a simultaneous relocation of the mainshocks aftershocks and background earthquakes it has been unclear whether the 1993 2001 and 2002 guam earthquakes m w 7 8 7 0 and 7 1 respectively in the southern mariana subduction zone were interplate events or intraplate ones within the pacific slab we relocated their mainshocks aftershocks and numerous long term background earthquakes simultaneously with high relative accuracy using the modified joint hypocenter determination mjhd method as a result their mainshocks and three day aftershocks are clearly distributed within the background slab seismicity therefore we conclude that the 1993 2001 and 2002 guam earthquakes were not interplate events which scarcely occur in the mariana subduction zone but intraslab earthquakes within the subducted pacific plate the 1993 fault plane is inferred to be the near horizontal nodal plane of the mechanism solution though the 2001 and 2002 fault planes remain unknown the relocation of target events simultaneously with background earthquakes has turned out very effective for discriminating between large interplate and intraslab earthquakes in subduction zones

detection of crustal deformation from the landers earthquake sequence using continuous geodetic measurements the measurement of crustal motions in technically active regions is being performed increasingly by the satellite based global positioning system gps 1 2 which offers considerable advantages over conventional geodetic techniques3 4 continuously operating gps arrays with ground based receivers spaced tens of kilometres apart have been established in central japan5 6 and southern california to monitor the spatial and temporal details of crustal deformation here we report the first measurements for a major earthquake by a continuously operating gps network the permanent gps geodetic array pgga 7 9 in southern california the landers magnitude afw of 7 3 and big bear mw 6 2 earthquakes of 28 june 1992 were monitored by daily observations ten weeks of measurements centred on the earthquake events indicate significant coseismic motion at all pgga sites significant post seismic motion at one site for two weeks after the earthquakes and no significant preseismic motion these measurements demonstrate the potential of gps monitoring for precise detection of precursory and aftershock seismic deformation in the near and far field

the great kurile earthquake of october 4 1994 tore the slab the fault geometry depth and slip distribution of the kurile earthquake of oct 4 1994 are estimated using seismic waveforms aftershock distribution geodetic measurements and tsunami waveforms previous large earthquakes in the kurile arc had typical underthrusting focal mechanisms due to the local subduction seismic wave inversions of the 1994 event indicate a thrust type mechanism with a large strike slip component this does not represent an underthrust event at the subduction interface the focal depth is estimated at 50 kin just beneath the previously estimated subduction interface we calculate crustal deformation and tsunami waveforms from the two possible fault planes of the focal mechanism solution and find that both fault planes explain the observations we choose the north south striking plane because of the occurrence of a large m w 7 8 intermediate depth earthquake on dec 6 1978 northwest of the 1994 rupture area the lineation of aftershock distributions of these two events suggests that both earthquakes were due to a tearing of the slab perpendicular to the trench the joint inversion of geodetic and tsunami data shows that the largest slip about 17 m occurred at the upper end of the slab

refined coseismic displacement modeling for the 1994 shikotan and sanriku oki earthquakes we consider refined modeling of gps measurements of coseismic displacement for two large earthquakes occurring in the japan and kurile trenches calculations are performed for a layered sphere and the homogeneous half space more commonly used to model such data using fault geometry and slip distributions from previously published studies we show that the difference between the layered sphere and homogeneous half space calculations can be significant as expected from previous theoretical studies however it does not appear large enough to seriously affect results from previously published studies of these earthquakes nevertheless the fact that the effects of sphericity and especially layering are measurable in coseismic observations of great earthquakes at moderate distances indicates that these effects should be taken into account in order to fully exploit the precision of modern gps measurements

on the geographical variability of the upper level mean and eddy fields in the north atlantic and north pacific abstract all available historical expendable bathythermograph data are used to compute means and standard deviations in temperature for the upper 500 m in the north atlantic and north pacific to take advantage of marked spatial differences in data coverage a variable grid scheme is employed both surface and subsurface annual mean temperature distributions agree well with published maps of these quantities climatological mean temperature salinity and salinity depth curves are used to infer salinities for the mean temperature profiles in order to compute 0 500 db inferred dynamic height and its standard deviation these mean curves are also used to compute eddy potential energy at 300 m the maps of mean annual inferred dynamic height agree well with traditional dynamic height maps and appear similar to the maps of mean temperature at 400 m the north atlantic eddy potential energy distribution is similar to an earlier calculation maps of the standard deviations in inferred dynamic height also represent

the october 4 1994 shikotan kurile islands tsunamigenic earthquake an open problem on the source mechanism on october 4 1994 an earthquake of magnitude m w 8 2 occurred in the western part of the kurile islands generating a tsunami that has been well recorded along the entire coast of japan previous works have shown that this earthquake does not represent a low angle thrust event normally expected in a subduction zone rather an intra plate event rupturing through the slab on the basis of the accepted mechanism two fault models representative of the nodal plane ambiguity have been suggested the goal of this work is to verify whether the tsunami simulations are able to rule out one of the two proposed fault models taking into account both fault models together with a heterogeneous slip along the fault we have performed numerical simulations of the tsunami all source models produce tide gauge records in agreement with the observed ones the limit of resolution of the performed simulations estimated by means of a perturbed bathymetry does not allow us to distinguish the best source model

scientific objectives of current and future wegener activities abstract the wegener group has promoted the development of scientific space geodetic activities in the mediterranean and in the european area for the last fifteen years and has contributed to the establishment of geodetic networks designed particularly for earth science research wegener currently has three scientific objectives which are related to plate boundary processes sea level and height changes and postglacial rebound in a full exploitation of the space geodetic techniques namely slr vlbi and gps the individual scientific projects do not only pursue these objectives but also contribute to improving and developing the observation techniques as well as the modelling theories in the past particularly slr observations within wegener medlas have provided a fundamental contribution to determine the regional kinematics of the tectonic plates in the mediterranean with high precision with gps spatially denser site distributions are feasible and in several wegener projects detailed studies of tectonically active areas were possible on the basis of repeated episodic gps observations current projects associated with wegener are successful in separating crustal movements and absolute sea level variations as well as in monitoring postglacial rebound these tasks require high precision height determinations a problem central to all of the present wegener activities in these projects continuously occupied gps sites are of increasing importance time series of heights observed with continuous gps can be determined with a few centimeters rms error thus enabling the reliable estimates of vertical rates over relatively short time intervals regional networks of continuous gps sites are already providing results relevant for example for the study of postglacial rebound the mediterranean area is an extraordinary natural laboratory for the study of seismotectonic processes and the wealth of observations acquired in previous wegener projects together with new space geodetic observations will allow the test of geophysical hypotheses linking three dimensional deformations of the earth s surface to the dynamics of the earth s interior in particular it is anticipated that wegener projects will aim at a test of the slab detachment hypothesis the complex investigations on sea level fluctuations presently carried out at basin scale from the strait of gibraltar to the black sea make it possible to study the present and recent past interactions of ocean atmosphere and solid earth as well as to develop appropriate models to assess future aspects

the 1994 hokkaido toho oki earthquake sequence the complex activity of intra slab and plate boundary earthquakes abstract we study the complex activity of the 1994 hokkaido toho oki earthquake sequence based on strong motion records and teleseismic data first we examine s wave acceleration spectra of the aftershocks by comparison with that of the main shock the main shock m w 8 2 an intra slab earthquake has been characterized by strong radiation of high frequency seismic waves from different shapes of the spectral ratios of the aftershocks to the main shock the aftershocks can be classified into three types next we redetermine the source parameters focal depth seismic moment and source duration for larger events by waveform modeling of teleseismic p waves the hypocentral locations and stress drops estimated from these parameters show that the three aftershock types fall into different categories of subduction zone earthquakes intra slab relatively deep plate boundary and shallow plate boundary earthquakes finally we estimate source spectra for three different earthquake categories after correcting s wave acceleration spectra for the attenuation effect the source spectrum at high frequencies is modeled by using a high cut filter whose parameters are a cut off frequency f max and a decay rate the source spectrum of intra slab earthquakes has high f max and small decay rate due to this feature and the high stress drop intra slab earthquakes radiate strong high frequency seismic waves through this study we demonstrate that the 1994 hokkaido toho oki earthquake sequence has the complex activity of intra slab and plate boundary earthquakes

aftershock distribution of the october 4 1994 mw8 3 kurile islands earthquake determined by a local seismic network in hokkaido japan on october 4 1994 an earthquake with magnitude mw8 3 occurred in the western part of kurile islands at 43 42 n 146 81 e and 33 km in depth the hypocenter parameters were determined by hokkaido university in japan aftershocks following this remarkable event were located using data from a local seismic network operated by hokkaido university we found that most of the aftershocks occurred 1 on the fault plane of the mainshock 2 in the subducting plate around the fault plane of the mainshock and 3 in the focal area of the largest aftershock which occurred on october 9 with mw7 3 both 2 and 3 were not active immediately after the mainshock considering the time sequence of the aftershock activity we identified one of the nodal planes of the harvard quick cmt solutions as the fault plane of the mainshock the strike is almost parallel to the trench axis and the dip angle is near vertical it is obvious that this event is different from a low angle thrust type interplate earthquake the distribution of aftershocks strongly suggests that it is an intraplate event