a scaling law for slow earthquakes with the availability of the global positioning system and other technical advances a growing number of unusual earthquake phenomena occurring at relatively long periods have been recognized they include deep episodic tremor low frequency earthquakes slow slip events and silent earthquakes based on data chiefly from western japan ide et al report that these slow seismic events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes a diverse array of unusual earthquake phenomena occurring at relatively long periods slow events follow a unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes indicating that they comprise a new earthquake category recently a series of unusual earthquake phenomena have been discovered including deep episodic tremor1 low frequency earthquakes2 very low frequency earthquakes3 slow slip events4 and silent earthquakes5 6 7 8 9 each of these has been demonstrated to arise from shear slip just as do regular earthquakes but with longer characteristic durations and radiating much less seismic energy here we show that these slow events follow a simple unified scaling relationship that clearly differentiates their behaviour from that of regular earthquakes we find that their seismic moment is proportional to the characteristic duration and their moment rate function is constant with a spectral high frequency decay of f 1 this scaling and spectral behaviour demonstrates that they can be thought of as different manifestations of the same phenomena and that they comprise a new earthquake category the observed scale dependence of rupture velocity for these events can be explained by either a constant low stress drop model or a diffusional constant slip model this new scaling law unifies a diverse class of slow seismic events and may lead to a better understanding of the plate subduction process and large earthquake generation

correlation scales objective mapping and absolute geostrophic flow in the california current the spatial covariances of the time dependent density and geostrophic velocity fields off southern california are determined from a unique set of repeated hydrographic observations 44 cruises made by the california cooperative oceanic fisheries investigations from 1984 to 1994 the covariances and objective analysis are used to combine direct velocity observations from shipboard acoustic doppler current profiler adcp measurements made on a recent survey october 1993 with hydrographic observations the analysis reduces ageostrophic noise in the adcp velocities by smoothing and enforcing horizontal nondivergence additionally the velocities are mapped over scales that are dynamically consistent with the hydrography maximum surface geostrophic flow in the california current in october 1993 is about 35 cm s 1 50 larger than that estimated assuming a 500 m level of no motion absolute flow at 500 m is o 10 cm s 1 and indicates that the surface eddy field penetrates through the thermocline uncertainty in the geostrophic reference calculated from the adcp measurements is of o 4 cm s 1 the velocity residual objectively analyzed minus raw adcp estimates exhibits smaller correlation scales than the geostrophic flow

very low frequency earthquakes related to small asperities on the plate boundary interface at the locked to aseismic transition 1 very low frequency vlf seismic signals observed in southwestern japan are evidently radiated from shear slips on the upper surface of the subducting philippine sea plate we used grid moment tensor inversion and centroid moment tensor inversion to calculate 242 moment tensor solutions with moment magnitudes between 3 1 and 3 8 from continuous seismograms recorded over a 5 year period by using a very dense broadband seismic network at least 5 10 sequences of repetitive activity were observed during the 5 years the vlf events formed clustered distributions along the 35 km isodepth contour of the subducting plate surface the nodal planes which dip landward of moment tensor solutions of the vlf events reflected the configuration of the subducting plate interface the slip vectors were consistent with the direction of movement of the subducting plate the dip and strike of the slip vectors clearly reflected the configuration of the upper surface of the subducting plate we found that the rates of seismic moment release per unit area associated with five major vlf clusters were very similar although both the seismic magnitudes and sizes of the clusters varied considerably the rate of seismic moment released from detectable vlf sources was 0 1 of the rates of short term slow slip events suggesting that the source areas occupied only 0 1 of the fault segment on which the short term slow slip events occurred

mechanism of deep low frequency earthquakes further evidence that deep non volcanic tremor is generated by shear slip on the plate interface 1 we study the mechanism of low frequency earthquakes lfes in the nankai trough in western shikoku japan precise locations have previously suggested that they represent shear slip on the plate boundary in this paper we examine the mechanism of these events due to the low signal to noise ratio we analyze stacked lfe waveforms and compare them with the waveforms of nearby earthquakes of known mechanism within the subducting philippine sea plate analysis of both the focal mechanism using p wave first motions and the moment tensor using s waveforms indicates that lfes represent shear slip on a low angle thrust fault dipping to the northwest namely the plate interface together with reports that deep tremor consists of a swarm of lfes our results suggest that deep tremor is generated directly by shear slip on the plate interface and as such represents a seismic signature of the accompanying slow slip events

episodic slow slip events accompanied by non volcanic tremors in southwest japan subduction zone 1 episodic slow slip events have been recognized by means of tilt changes in the western shikoku area southwest japan the crustal tilt deformation was observed repeatedly with a recurrence interval of approximately six months coincident with the occurrences of major non volcanic deep tremor activities in this area observed tilt changes can be explained by slow slip events occurring around the source area of tremors in each episode the source of the slow slip event and tremor migrate simultaneously the spatial and temporal coincidence of tremors and slow slip events indicates that they both may be coupling phenomena reflecting the stress accumulation process at the subducting plate

north pacific thermocline variations on enso timescales abstract the north pacific thermocline 250 to 400 m is studied using xbt observations acquired during the 1970s and 1980s interannual variations 3 5 yr timescales in thermocline temperature with o 0 1 c amplitude at 400 m are found to exhibit westward propagation throughout the extratropical north pacific up to 45 n southward of 30 n the features propagate intact across the basin from the eastern boundary to the western boundary northward of 30 n the features can be observed to propagate only as far as the date line the observed midlatitude thermocline anomalies are often related to tropical enso events in that they occur most strongly after the development of tropical el nino or la nina conditions and propagate westward from near the eastern boundary in the midlatitudes but it is found that the observed midlatitude thermocline anomalies have larger phase speeds than theoretically predicted free baroclinic rossby waves also the observed anomalies have larger wavelength and faster propagati

a negative search for an ultra slow component to the source of the yunnan earthquakes of may 29 1976 abstract following nagamune s suggestion of a giant but very slow component to the source of the yunnan earthquakes of may 29 1976 a systematic study of the ultra low frequency content of a number of tiltmeter strainmeter and ida records of the events is conducted first nagamune s hypothesis is quantified and it is found that it would require a moment in the range 10 29 10 30 dyn cm such a large moment would have important consequences for our understanding of stress release in the plates but is incompatible with the extent of the aftershock zone and with observations on other instruments specifically only one ida record shows a time domain oscillation which may be related to the proposed source in the fourier domain however a spectral analysis fails to identify any of the earth s modes in any of the available records including the one originally used by nagamune it must therefore be concluded that the apparent signal present in a few records is due to noise probably of instrumental origin rather than to an ultra low frequency component of the seismic source

30 million years of permian volcanism recorded in the choiyoi igneous province w argentina and their source for younger ash fall deposits in the parana basin shrimp u pb zircon geochronology evidence abstract we present four shrimp u pb zircon ages for the choiyoi igneous province from the san rafael block central western argentina dated samples come from the yacimiento los reyunos formation 281 4 2 5 ma of the cochico group lower choiyoi section andesitic breccias dacitic to rhyolitic ignimbrites and continental conglomerates agua de los burros formation 264 8 2 3 ma and 264 5 3 0 ma and cerro carrizalito formation 251 9 2 7 ma upper choiyoi section rhyolitic ignimbrites and pyroclastic flows spanning the entire permian succession of the choiyoi igneous province a single zircon from the el imperial formation that is overlain unconformably by the choiyoi succession yielded an early permian age 297 2 5 3 ma while the main detrital zircon population indicated an ordovician age 453 7 8 1 ma the new data establishes a more precise permian age artinskian lopingian for the section studied spanning 30 ma of volcanic activity volcanological observations for the choiyoi succession support the occurrence of explosive eruptions of plinian to ultraplinian magnitudes capable of injecting enormous volumes of tephra in the troposphere stratosphere the new shrimp ages indicate contemporaneity between the choyoi succession and the upper part of the parana basin late paleozoic section from the irati up to the rio do rasto formations encompassing about 24 ma geochemical data show a general congruence in compositional and tectonic settings between the volcanics and parana basin permian ash fall derived layers of bentonites thickness and granulometry of ash fall layers broadly fit into the depletion curve versus distance from the remote source vent of ultraplinian eruptions thus we consider that the choiyoi igneous province was the source of ash fall deposits in the upper permian section of the parana basin data presented here allow a more consistent correlation between tectono volcanic permian events along the paleo pacific margin of southwestern gondwana and the geological evolution of neighboring paleozoic foreland basins in south america and africa

low frequency variability of the north pacific ocean the roles of boundary and wind driven baroclinic rossby waves 1 the effects of the sea level variability along the eastern boundary of the north pacific ocean including those associated with el nino southern oscillation have been considered an important factor in determining the low frequency large scale variability of the ocean interior through rossby waves generated at the eastern boundary this hypothesis is examined in this study using 8 years worth of the sea surface height observations made by the topex poseidon satellite the timescales of interest are longer than 90 days with the annual cycle removed the results indicate that the influence of the eastern boundary of the north pacific ocean has limited offshore extent varying from 3000 4000 km at 10 n to 200 300 km at 50 n the variability in the ocean interior is primarily driven by wind with only a minor influence from the boundary simulations of a linear two layer model of the ocean driven by wind stress curl are correlated with the observations the effects of wind forcing accumulate along the characteristics of long nondispersive rossby waves in the time longitude domain these wind driven rossby waves overwhelm the boundary driven waves in the ocean interior where there are only some small residual effects of the boundary driven waves however these small effects become clearer after the simulated wind driven variability is removed from the observations index terms 4556 oceanography physical sea level variations 4504 oceanography physical air sea interactions 0312 4215 oceanography general climate and interannual variability 3309 keywords rossby waves satellite altimetry el nino north pacific eastern boundary

on too fast baroclinic planetary waves in the general circulation abstract recent altimetric observations of the ocean surface reveal signatures of long planetary waves near the annual frequency band comparisons of the observed wave speeds and those predicted by standard linear theory suggest that the latter is inadequate as it yields different westward speeds than those measured in the extratropical latitudes the predicted speeds are typically slower than the observations here the problem of long baroclinic wave propagation in a forced stratified ocean is considered theoretically with a view toward explaining these observations of too fast planetary waves from a quasigeostrophic analysis it is argued that baroclinic waves in a sheared environment are accelerated to the west via their interactions with both the mean advective field and the mean potential vorticity field conditions under which the ratio of actual to linear phase speeds matches the observed ratio are computed and found to be typical of the open ocean extensions of these ideas to continuously st

thermal constraints on the seismogenic portion of the southwestern japan subduction thrust for coastal cities an important factor in earthquake hazard from subduction zone earthquakes is the landward extent of the seismogenic portion of the subduction thrust fault in this study we test the hypothesis that the maximum downdip extent is defined by a critical temperature we have developed a transient thermal model for the nankai subduction zone of southwest japan to allow comparison of the thermally estimated downdip extent of the seismogenic zone with that from 1 seismicity and tsunami data for two great subduction earthquakes 2 the coseismic faulting extent of these events estimated from geodetic deformation data and 3 the interseismic locked zone determined from interseismic geodetic data the nankai margin has extensive heat flow and heat production data to control thermal models and thus crustal temperatures it has earthquake tsunami and geodetic data that constrain the coseismic rupture portion of the subduction thrust fault for past great earthquakes and the portion of the thrust fault that is locked and storing interseismic elastic strain on the nankaido margin off shikoku island the thermal model indicates that a temperature of 350 c taken to be the limit for seismic initiation from laboratory and field data is reached on the subduction thrust fault 150 km from the trench a transition zone into which rupture may extend with decreasing offset taken to be 450 c extends an additional 45 km downdip the thermal model results are in excellent agreement with the maximum downdip extent of coseismic displacement for the 1946 nankaido ms 8 2 earthquake off shikoku island and with the downdip extent of the present locked zone in the region of the 1944 tonankai ms 8 2 earthquake to the northeast the subduction angle is much steeper and the thermal models indicate a narrower downdip seismogenic extent the seismogenic locked zone from earthquake and geodetic data is also narrower thus our analysis of the southwest japan margin indicates that all three constraints on the downdip extent of the seismogenic zone thermal coseismic and interseismic geodetic data are in general agreement the study also supports the hypothesis that the seismogenic portion of subduction thrust faults is limited primarily by temperature the thermal control implies that subduction thrust faults with shallow dip have wider seismogenic zones compared to those with steep dip the subducting plate age and thus heat flow and the thickness of the insulating sediments on the incoming plate are also very important to the thermal regime and thus to the seismogenic width the relation of the maximum seismic rupture area to the interseismic locked zone is particularly important for earthquake hazard estimation on subduction margins such as cascadia where there have been no great historical events

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

el nino sea level and currents along the south american coast comparison of observations with theory abstract interannual sea level fluctuations along the south american coast and 7 3 year long current records at 30 s off central chile were examined with a low frequency linear numerical model the model includes stratification and shelf and slope bottom topography which varies alongshore the coastal flow is driven by interannual alongshore wind stress and an interannual alongshore pressure gradient resulting from el nino la nina pressure fluctuations at the equator calculations suggest that along the south american coast the coastal interannual variability is primarily due to the remote equatorial forcing rather than interannual coastal alongshore wind stress past work using this model has shown that due to the scattering of lower vertical modes to higher ones by bottom friction the model predicts a low frequency jet trapped near the bottom along the continental slope until now adequate interannual current time series were unavailable to check this prediction analysis of the observations shows th

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

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

critical frequencies at ocean boundaries past theoretical work has shown that for low frequency flow at a given ocean boundary location a critical frequency c exists such that for c unforced motion is trapped to the coast while for c energy leaves the coast alternatively for motion of a given frequency on the boundary there exists a critical latitude such that the motion is trapped to the coast poleward of that latitude but equatorward it is not this theory is discussed physically for both meridional and nonmeridional boundaries the simple formula for critical frequency along a nonmeridional boundary is used to document critical periods for the eastern and western atlantic pacific and indian ocean boundaries the theory occasionally breaks down when boundary curvature is too large

characteristic small earthquake sequence off sanriku northeastern honshu japan 1 we found eight similar earthquakes of m4 8 regularly occurring from 1957 to 1995 on the plate boundary off sanriku northeastern japan the mean recurrence interval of the events is 5 35 years and its standard deviation is only 0 53 years these events have the same focal mechanisms of low angle thrust fault type and their source sizes are estimated to be around 1 km the slip of each event is comparable to the cumulative amount of relative plate motion in the inter seismic period thus these events are probably caused by repeating slip at a small but strong asperity surrounded by creeping zone on the plate boundary the next event was expected to occur by the end of november 2001 with 99 probability and actually m4 7 event occurred on november 13 2001

planetary wave propagation off california and its effect on zooplankton abstract lagged correlation of dynamic height from the gappy california cooperative oceanic fisheries investigation calcofi with monthly san diego sea level for the period 1949 2001 shows that the dynamic height propagates westward at 4 10 cm s 1 about double the speed of the large scale low frequency rossby wave 2 2 cm s 1 ocean topography experiment topex poseidon jason 1 s along track sea level height estimates since january 1993 filtered interannually propagate westward at 4 3 cm s 1 verifying that observed westward propagation is about double that expected including the effect of the mean california current on the rossby wave propagation does not explain the discrepancy but rather slightly increases it if variations in the ocean depth in the calcofi region are also taken into account the westward propagation is still only about one half that observed standard theory therefore does not explain the observations because of the westward propagation interannual variations in alongshore ge

circulation and multiple scale variability in the southern california bight abstract the oceanic circulation in the southern california bight scb is influenced by the large scale california current offshore tropical remote forcing through the coastal wave guide alongshore and local atmospheric forcing the region is characterized by local complexity in the topography and coastline all these factors engender variability in the circulation on interannual seasonal and intraseasonal time scales this study applies the regional oceanic modeling system roms to the scb circulation and its multiple scale variability the model is configured in three levels of nested grids with the parent grid covering the whole us west coast the first child grid covers a large southern domain and the third grid zooms in on the scb region the three horizontal grid resolutions are 20 km 6 7 km and 1 km respectively the external forcings are momentum heat and freshwater flux at the surface and adaptive nudging to gyre scale soda reanalysis fields at the boundaries the momentum flux is from a three hourly reanalysis mesoscale mm5 wind with a 6 km resolution for the finest grid in the scb the oceanic model starts in an equilibrium state from a multiple year cyclical climatology run and then it is integrated from years 1996 through 2003 in this paper the 8 year simulation at the 1 km resolution is analyzed and assessed against extensive observational data high frequency hf radar data current meters acoustic doppler current profilers adcp data hydrographic measurements tide gauges drifters altimeters and radiometers the simulation shows that the domain scale surface circulation in the scb is characterized by the southern california cyclonic gyre comprised of the offshore equatorward california current system and the onshore poleward southern california countercurrent the simulation also exhibits three subdomain scale persistent i e standing cyclonic eddies related to the local topography and wind forcing the santa barbara channel eddy the central scb eddy and the catalina clemente eddy comparisons with observational data reveal that roms reproduces a realistic mean state of the scb oceanic circulation as well as its interannual mainly as a local manifestation of an enso event seasonal and intraseasonal eddy scale variations we find high correlations of the wind curl with both the alongshore pressure gradient apg and the eddy kinetic energy level in their variations on time scales of seasons and longer the geostrophic currents are much stronger than the wind driven ekman flows at the surface the model exhibits intrinsic eddy variability with strong topographically related heterogeneity westward propagating rossby waves and poleward propagating coastally trapped waves albeit with smaller amplitude than observed due to missing high frequency variations in the southern boundary conditions

dynamics of wind driven upwelling and relaxation between monterey bay and point arena local regional and gyre scale controls 1 in north and central california equatorward winds drive equatorward flows and the upwelling of cold dense water over the shelf during the midspring and summer upwelling season when the winds temporarily weaken the upwelling flows between point reyes and point arena relax becoming strongly poleward over the shelf analytical and numerical models are used to describe the effect of alongshore variability of winds bathymetry and basin scale pressure gradients on the strength of upwelling and its relaxation alongshore winds weaken to the south of point reyes and the shelf becomes narrower from point reyes to monterey bay both of these lead to reduced upwelling at and to the north of point reyes causing an alongshore gradient of temperature and density on the shelf these alongshore gradients lead to an along isobath pressure gradient over the shelf that drive the relaxation flows a simple analytical model is used to explain the dynamics magnitude and structure of the relaxation flows the modeling also suggests that the depth of origin of the upwelled waters and thus their temperature is controlled by the along isobath pressure gradient that exists over the continental slope this along slope pressure gradient is also responsible for the california undercurrent in this region this pressure gradient is not generated in a model of the californian coast extending from 32 n to 42 n and integrated for several months suggesting it is caused by dynamics whose spatial or temporal scales are larger than the californian coast and or longer than several months

bridging the gap between seismically and geodetically detected slow earthquakes 1 recently observed unusual seismic events deep low frequency earthquakes and tremor very low frequency earthquakes and slow slip events form a family of slow earthquakes that are governed by a scaling law different from ordinary earthquakes guided by this scaling law we have observed previously unknown events with source duration of 20 200 s and moment magnitude of 3 4 under the kii peninsula in western japan these events radiate seismic energy in the 2 8 hz band in direct proportion to their seismic moment rate though the constant of proportionality is 4 5 orders of magnitude smaller than for ordinary earthquakes slow earthquakes in this region may be comprised of numerous shear slip events which in aggregate are manifest seismically as tremor or isolated longer events up to 200 s and geodetically as slow slip events

rossby waves and the interannual and interdecadal variability of temperature and salinity off california abstract previous work has shown that large scale interannual rossby waves largely remotely generated by equatorial winds propagate westward from the coast off southern california these waves have a large scale anomalous alongshore velocity field that is proportional to the time derivative of the interannual sea level anomaly using these results a theory is developed for interannual perturbations to a mean density field that varies both vertically and alongshore like that for the california current region off southern california because both the anomalous vertical and alongshore currents are proportional to the time derivative of the interannual sea level the theory suggests that the anomalous currents associated with the rossby waves acting on the mean temperature field should induce temperature fluctuations proportional to the anomalous dynamic height the alongshore and vertical advections contribute to the temperature fluctuations in the same sense a higher than normal sea level for exampl

on the propagation of baroclinic waves in the general circulation the propagation of long first mode baroclinic planetary waves in eddy resolving quasigeostrophic general circulation models is studied recent topex poseidon observations argue oceanic first mode planetary waves move with speeds other than those predicted by simple theory these data have prompted theoretical analyses of wave propagation in a mean flow with the results suggesting mean shear can have a controlling effect on the planetary wave guide some of the predicted effects appear to be relevant to the observations while others are less obvious this coupled with other explanations for the observations motivates the calculations based on these experiments the authors suggest that the predicted effects of mean shear on wave propagation are consistent with those computed in a fully geostrophically turbulent ocean these are that a two layer model misses the dominant component of long wave interaction with a mean flow a three layer model captures this interaction qualitatively and the correction to wave propagation is in the direction opposite to the mean flow quantitative comparisons between the theory and the numerical experiments are good in the northern latitudes and questionable in the southern latitudes reasons for the southern discrepancy are offered

scaling relationship between the duration and the amplitude of non volcanic deep low frequency tremors 1 we investigate a duration amplitude relation of non volcanic deep low frequency dlf tremors in the tokai region southwest japan to constrain the source process of the tremors we apply two models to the distribution one is an exponential model as a scale bound distribution and the other a power law model as a scale invariant distribution the exponential model shows a better fit to the duration amplitude distribution of the tremors than a power law model implying that the dlf tremors are caused by a scale bound source process the source process of the dlf tremors therefore differs from those for earthquakes we suggest that the non volcanic dlf tremor is possibly caused by a fixed source dimension with variable excess pressure of fluid or variable stress drop

sources of interannual baroclinic waves in the eastern subtropical north pacific abstract subsurface temperature and surface salinity observations along the great circle transect between san francisco and honolulu are used to investigate the source of annual baroclinic long waves in the eastern subtropical north pacific ocean long term mean 15 day values 1966 74 of depth of the 9 c isotherm indicative of thermocline depth and of surface salinity are each fit by least squares method with a time varying cosine yielding phase and amplitude of the mean annual cycle at standard locations every 92 6 km 50 mi along the transect local wind stress curl is expected to influence the observed depth of the 9 c isotherm through the mechanism of ekman pumping therefore its annual cycle is computed in a manner like that of the depth of the 9 c isotherm and its effect removed from the latter the residual annual cycle has phase and amplitude profiles along the transect that closely resemble that of model annual baroclinic long waves emanating from a line source of large amplitude wind st

the effect of bottom topography on the speed of long extratropical planetary waves abstract this paper examines how slowly varying topography induces changes in all aspects of long planetary wave propagation including phase speed and surface signature through steering effects the approach introduces a method for the exact solution of the vertical topographic eigenvalue problem for arbitrary realistic stratification and ray theory in the horizontal it is shown that for observed stratifications first internal mode topographic waves have phase speeds between about 0 4 and twice the local flat bottom phase speed increases occur on the western and equatorward sides of hills focusing of ray trajectories and caustics are common features of the solutions despite a bias between slowdown and speedup on average there is little speedup except in high latitudes where long wave theory is less applicable calculations are performed for five main ocean basins assuming waves are generated at the eastern coastline using smoothed topography these calculations confirm the above findings the

low frequency continuous tremor around the moho discontinuity away from volcanoes in the southwest japan 1 recent enhancement of seismic networks in the japan islands revealed occurrence of low frequency continuous tremors of a beltlike distribution in the southwest japan where the subducting philippine sea plate reaches depths of 30 40 km source depth of the tremor is estimated by selecting tremor segments with relatively clear p wave onsets the source region of the tremor is assumed to correspond to lowermost parts of crust close to a triple boundary of the crust mantle wedge and the subducting slab the long duration of the phenomenon indicates existence of fluid relating to the generation of the tremor the most probable fluid is considered to be water produced by dehydration process of chlorite and amphibole in the slab on the basis of data from high pressure and temperature experiments the northern border of the beltlike distribution is possibly rimmed by the edge of the mantle wedge because serpentine formation absorbs fluid water

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

long extratropical planetary wave propagation in the presence of slowly varying mean flow and bottom topography part i the local problem one of the most successful theories to date to explain why observed planetary waves propagate westward faster than linear flat bottom theory predicts has been to include the effect of background baroclinic mean flow which modifies the potential vorticity waveguide in which the waves propagate barotropic flows are almost everywhere too small to explain the observed differences that theory accounted for most but not all of the observed wave speeds a later attempt to examine the effect of the sloping bottom on these waves without the mean flow effect did not find any overall speedup this paper combines these two effects assuming long geostrophic waves and slowly varying mean flow and topography and computes group velocities at each point in the global ocean these velocities turn out to be largely independent of the orientation of the wave vector a second speedup of the waves is found over that for mean flow only almost no eastward oriented group velocities are found and so features that appear to propagate in the same sense as a subtropical gyre would have to be coupled with the atmosphere or be density compensated in some manner

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

the effect of bottom pressure decoupling on the speed of extratropical baroclinic rossby waves abstract in layered models of the ocean the assumption of a deep resting layer is often made motivated by the surface intensification of many phenomena the propagation speed of first mode baroclinic rossby waves in such models is always faster than in models with all the layers active the assumption of a deep resting layer is not crucial for the phase speed enhancement since the same result holds if the bottom pressure fluctuations are uncorrelated from the overlying wave dynamics in this paper the authors explore the relevance of this behavior to recent observational estimates of too fast waves by chelton and schlax the available evidence supporting this scenario is reviewed and a method that extends the idea to a continuously stratified fluid is developed it is established that the resulting amplification factor is at leading order captured by the formula where cfast is the enhanced phase speed cstandard the standard phase speed 1 z is the standard first mode for the velocity and pressur