advective transport caused by intraseasonal rossby waves a key player of the high chlorophyll variability off the peru upwelling region 1 the upwelling region off peru between 5 s and 12 s is characterized by high offshore intraseasonal variability in sea surface productivity due to westward propagating chlorophyll anomalies whose magnitude can reach half the variance of total chlorophyll variations spectral analyses of ssh sst and chlorophyll satellite data show that these events are generated by intraseasonal rossby waves the almost constant phase shift between chlorophyll and altimetric signals suggests a physical mechanism dominated by horizontal advection which is confirmed by the use of a simple conceptual model furthermore an increase from the north to the south in the detected rossby wave periods correlated with a decrease in the wavelengths and phase velocities of the wave suggests the presence of a second baroclinic mode north of 8 s and of a first baroclinic mode south of this latitude the latitude of this transition is consistent with the theory of critical latitudes which specifies that at a given latitude only rossby wave with periods below a threshold period depending on the baroclinic structure of the wave can propagate offshore according to this theory second baroclinic mode rossby waves with periods greater than 130 days are supposed to propagate off the south american coast north of 8 s the corresponding critical latitude

formation of a basin scale surface chlorophyll pattern by rossby waves the enhancement of surface chlorophyll by rossby waves which has recently been detected in bandpass filtered ocean color data cipollini et al 2001 uz et al 2001 is shown to be intense enough to form a dominant pattern in monthly mean basin scale ocean color satellite maps of the indian ocean results from a biological physical coupled model suggest that this phenomenon which is visible predominantly in austral winter is caused by rossby wave induced upwelling that lifts the deep chlorophyll maximum dcm into contact with the surface mixed layer ml the model results suggest that these events are not associated with any significant input of nutrients into the ml while the temporal enhancement of regional primary production by rossby waves is substantial 30 it is not necessarily associated with a corresponding increase in surface chlorophyll e g when the ml is too shallow to touch the dcm and may hence escape detectability by satellite measurements

impact of a coastal trapped wave on the near coastal circulation of the peru upwelling system from glider data alongshore velocity data from a glider repetitive section off the coast of peru 14 s are used to study the cross shore structure and temporal variability of the peru current system during a 5 week period in april may 2010 besides providing substantial information on the surface frontal jet associated with the peru coastal current and the surfacing peru chile undercurrent that flows poleward trapped on the continental shelf and slope the glider data reveal the presence of an intense deep equatorward current which transports up to 2 5 sv the dynamics of this current are investigated using an eddy resolving regional model the variability of the vertically sheared alongshore flow is shown to be related to the passage of a poleward propagating coastal trapped wave likely of equatorial origin solutions from a two dimensional linear coastal wave model suggest that the alongshore current observed vertical structure is associated with the second and third baroclinic modes of the coastal trapped wave

physical and biological mechanisms for planetary waves observed in satellite derived chlorophyll we examine the evidence for global propagation of planetary wavelike features in sea surface chlorophyll over much of the midlatitude ocean westward propagating signals are seen that travel at the same speed as that predicted for long planetary waves we then test three mechanisms for production of this signal these are horizontal passive north south advection by the wave against a mean background gradient vertical upwelling of nitrate which is converted into chlorophyll and vertical upwelling of chlorophyll itself the tests involve comparisons of the amplitude and phase of the predicted signal with observations the horizontal advective process predicts an amplitude for chlorophyll fluctuations that is in fair agreement with the data though both overestimating and underestimating in places the predictions for the phase difference between the chlorophyll and sea surface height signatures are in good agreement with the data the upwelling biological mechanism could potentially give a large signal in the chlorophyll field but the predicted amplitude patterns and the predicted phase difference which is everywhere negative are not in accord with the observations except in a few regions the amplitude predicted by upwelling of chlorophyll is small compared with the horizontal advection mechanism we conclude that over most of the ocean the chlorophyll signal is well explained by horizontal advective processes although we cannot rule out that there exist locations where additional biological mechanisms may be responsible for at least part of the signal

evolution of 1996 1999 la nina and el nino conditions off the western coast of south america a remote sensing perspective 1 we present the evolution of oceanographic conditions off the western coast of south america between 1996 and 1999 including the cold periods of 1996 and 1998 1999 and the 1997 1998 el nino using satellite observations of sea level winds sea surface temperature sst and chlorophyll concentration following a period of cold sst and low sea levels in 1996 both were anomalously high between march 1997 and may 1998 the anomalies were greatest between 5 s and 15 s although they extended beyond 40 s two distinct peaks in sea level and sst occurred in june july 1997 and december 1997 to january 1998 separated by a relaxation period august november of weaker anomalies satellite winds were upwelling favorable throughout the time period for most of the region and in fact increased between november 1997 and march 1998 between 5 s and 25 s satellite derived chlorophyll concentrations are available for november 1996 to june 1997 ocean color and temperature sensor octs and then from october 1997 to present sea viewing wide field of view sensor seawifs near surface chlorophyll concentrations fell from may to june 1997 and from december 1997 to march 1998 the decrease was more pronounced in northern chile than off the coast of peru or central chile and was stronger for larger cross shelf averaging bins since nearshore concentrations remained relatively high

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

a seismicity gap beneath the inner wall of the japan trench as derived by ocean bottom seismograph measurement abstract an ocean bottom seismograph obs array covered the area of the japan trench about 40 n off the tohoku district of northeastern honshu japan the obs array was operated for two weeks in june 1981 arrival time data of 8 obss were used to study a spatial distribution of microearthquakes around the trench during the observation period 400 500 events with a signal to noise ratio greater than 2 were detected by each obs the arrival times of 223 of these events could be picked 38 earthquakes were located in the area of the japan trench within the latitude range of 38 5 41 0 n and the longitude range of 142 0 146 0 e and about a hundred events were located beneath or near honshu island s p time distribution recorded by each obs showed seismic activities to exist on both sides of the trench axis while the seismic level was low beneath the inner wall of the trench epicentral distribution showed a seismicity gap beneath the inner wall of the trench the area of the landward activity continued eastward up to the position where the water depth is about 4000 m seismic activity existed beneath the trench axis and the seaward wall of the trench the seismicity gap suggested from the 1980 obs observations in the vicinity of the present study area was clearly confirmed by the present observations the obs array enabled us to determine the focal depth of microearthquake activity with better resolution than was possible from land observations the obs data showed that the landward activity beneath the continental slope was concentrated in the very shallow part of the lithosphere at a depth less than 30 km foci started to deepen westward with a very low dip angle of less than 10 which was the most shallow part of the upper plane of the double seismic zone the focal depth distribution showed that events just beneath the trench axis occurred to depths slightly greater than 50 km while the foci of the seaward activity were concentrated in the uppermost lithosphere at depths less than 30 km seismic cross sections clearly show that the activity beneath the trench axis and seaward wall of the trench is separated from the landward activity which is a shallow extension of the double seismic zone by the seismicity gap

inversion of tsunami waveforms for the estimation of heterogeneous fault motion of large submarine earthquakes the 1968 tokachi oki and 1983 japan sea earthquakes waveform inversion of tsunami data provides independent and reliable information on earthquake source processes the propagation effects of tsunamis are accounted for by computing green s functions using a finite difference method and using the known bathymetry which is much better constrained than the seismic velocity structure the observed tsunami waveforms are corrected for the response of the tide gage system by using the results of in situ measurements using green s functions computed from bathymetric data on a 2 5 km grid and the observed waveforms digitized at 1 min intervals the spatial resolution of the faulting heterogeneity by the present method is as small as 30 km this method is applied to the 1968 tokachi oki and 1983 japan sea earthquakes the slip is concentrated at the northwestern part of the fault plane for the 1968 event for the 1983 event the slip on the fault just north of the epicenter is twice that of the other parts these asperity distributions are similar to those inferred from seismic wave analysis however the recovered total seismic moments are smaller the present method is shown to be a useful technique for estimating heterogeneous fault motion especially for historical events with no or poor seismic records and tsunami earthquakes in which the excitations of seismic and tsunami waves are different

spatial distribution of earthquakes associated with the pacific plate subduction off northeastern japan revealed by ocean bottom and land observation abstract precise earthquake locations in the vicinity of a trench axis elucidate the characteristics of the shallower part of a subducting plate we split the japan trench into two regions off sanriku in the north and off fukushima in the south on the basis of the seismic properties of the regions and the fine microearthquake structure investigated by ocean bottom seismographic surveys as well as recent observation of major seismic activity from ocean bottom seismograph data the hypocentral distributions along a profile perpendicular to the trench axis indicate that almost all earthquakes occur along the boundary separating the subducting pacific plate and the landward plate a difference of the hypocentral distribution between off fukushima and off sanriku is found at the shallow plate boundary level the seismic thrust zone begins at more than 100 km landwards from the trench axis off fukushima whereas it begins at 50 km off sanriku and is nearly flat between 50 and 100 km from the trench axis this reflects regional variations of the interplate coupling in spite of these variations a common characteristic in recent observations indicates that in both regions almost all the hypocenters are deeper than 10 km this suggests the plate boundary to be decoupled at least in the part shallower than 10 km

linear and nonlinear computations of the 1992 nicaragua earthquake tsunami numerical computations of tsunamis are made for the 1992 nicaragua earthquake using different governing equations bottom frictional values and bathymetry data the results are compared with each other as well as with the observations both tide gauge records and runup heights comparison of the observed and computed tsunami waveforms indicates that the use of detailed bathymetry data with a small grid size is more effective than to include nonlinear terms in tsunami computation linear computation overestimates the amplitude for the later phase than the first arrival particularly when the amplitude becomes large the computed amplitudes along the coast from nonlinear computation are much smaller than the observed tsunami runup heights the average ratio or the amplification factor is estimated to be 3 in the present case when the grid size of 1 minute is used the factor however may depend on the grid size for the computation

modulation of chlorophyll concentration by downwelling rossby waves during the winter monsoon in the southeastern arabian sea abstract signatures of rossby waves that are evident in satellite ocean colour data in the southeastern arabian sea seas are more prominent during the winter than the summer monsoon during the winter the sea level is high and the conditions are less conducive for the injection of nutrients through the eddy pumping mechanism in this study we use satellite observations and a physical ecosystem model to examine the role of horizontal advection associated with rossby waves in enhancing chlorophyll concentration in the seas zonal advection dominates over meridional advection and its effect is more prominent in the south of indian subcontinent and west of the maldives except along the coast and around the islands the vertical processes are weak and do not lead to a substantial increase in chlorophyll model simulations show that the currents associated with the rossby wave also transport nutrients and other physicochemical properties of water along the path of the wave the advected water decreases the concentration of arabian sea high salinity water mass and replenishes the oxygen in the oxygen minimum zone in the seas

three stage rupture process of the 28 december 1994 sanriku oki earthquake we investigated the rupture process of the 28 december 1994 sanriku oki earthquake mw 7 7 using broadband seismograms recorded at local distances the earthquake rupture nucleated at the eastern end of the aftershock area as it propagated towards the west a major subevent occurred near the center of the aftershock area about 26 s after the initial rupture releasing most of the seismic energy of this earthquake about 24 s later another subevent followed at the western end of the aftershock area emitting large high frequency waves the whole rupture time is about 55 sec the three stage rupture process is very similar to the earlier stage rupture process of the 1968 tokachi oki earthquake mw 8 2 the difference is that the rupture of the tokachi oki earthquake further propagated towards the north in the following stage instead of terminating at the western end the occurrence of the sanriku oki earthquake is critical to the validity of the characteristic earthquake so far believed to exist in this part of the plate boundary

rupture process of large earthquakes in the northern mexico subduction zone the cocos plate subducts beneath north america at the mexico trench the northernmost segment of this trench between the orozco and rivera fracture zones has ruptured in a sequence of five large earthquakes from 1973 to 1985 the jan 30 1973 colima event m s 7 5 at the northern end of the segment near rivera fracture zone the mar 14 1979 petatlan event m s 7 6 at the southern end of the segment on the orozco fracture zone the oct 25 1981 playa azul event m s 7 3 in the middle of the michoacan gap the sept 19 1985 michoacan mainshock m s 8 1 and the sept 21 1985 michoacan aftershock m s 7 6 that reruptured part of the petatlan zone body wave inversion for the rupture process of these earthquakes finds the best earthquake depth focal mechanism overall source time function and seismic moment for each earthquake in addition we have determined spatial concentrations of seismic moment release for the colima earthquake and the michoacan mainshock and aftershock these spatial concentrations of slip are interpreted as asperities and the resultant asperity distribution for mexico is compared to other subduction zones the body wave inversion technique also determines the moment tensor rate functions but there is no evidence for statistically significant changes in the moment tensor during rupture for any of the five earthquakes an appendix describes the moment tensor rate functions methodology in detail

manifestation of oceanic rossby waves in long term multiparametric satellite datasets the characteristics of westward copropagating features in satellite altimetry sea surface temperature and ocean colour data are investigated throughout the global oceans between 50 north and 50 south for the period 1998 2008 a new hybrid filtering approach allowing features with periods between 37 and 410 days to pass polewards of 20 north and south and features with periods between 37 and 205 days to pass within 20 of the equator is found to isolate features whose speed is consistent with predictions of long planetary wave theory throughout much of the oceans features with wavelengths between 300 and 800 km and periods between 205 and 410 days are shown to be a significant source of temperature and chlorophyll variability between 20 and 50 north and south whilst within 20 of the equator signals in the 800 1500 km and 37 205 days range are predominant between 15 and 50 north and south observed propagation speeds are found to closely match those predicted for first mode baroclinic rossby waves by theory in the equatorial pacific and atlantic oceans features with wavelengths 800 2000 km periods 15 40 days and phase speeds 20 50 cm s 1 characteristic of tropical instability waves are preferentially observed the amplitude and phase relationship between copropagating signals in ocean colour and altimetry and sea surface temperature and altimetry is interpreted in terms of the horizontal meridional advection of mean temperature and chlorophyll gradients by rossby waves similar to what has recently been observed for non linear eddies at shorter length scales the observed phase relationships are in good agreement with the range of phases expected for horizontal advection throughout much of the oceans and consistent with the sign of the mean meridional gradients of temperature and chlorophyll these results support the view that horizontal advection be it from waves and or eddies is the dominant mode of covariation of temperature and chlorophyll with sea surface height throughout most of the oceans although the agreement between predicted and observed amplitude and phase relationships is insufficient to completely rule out vertical mechanisms in a few regions we believe that a one size fits all approach for global rossby wave studies can no longer be considered valid and although we have modified our technique to take this into account we advocate future work to develop a fully latitudinally dependent filtering methodology

depth of seismic coupling along subduction zones underthrusting at subduction zones can cause large earthquakes at shallow depths but it is always accommodated by aseismic deformation below a certain depth the maximum depth of the seismically coupled zone or seismogenic zone is a transition from unstable to stable sliding along the plate interface we have determined the depth of this stability transition for the circurn pacific subduction zones of honshu kuriles kamchatka aleutians alaska mexico and chile these subduction zones have experienced great interplate earthquakes and the aftershock regions are well located depth estimates of interplate events that are located at the downdip edge of the aftershock regions are used to determine the maximum depth of seismic coupling for an average p wave velocity of 6 7 km s 1 above the plate interface we find that for most subduction zones the stability transition occurs at 40 5 km depth there are however several exceptions at the hokkaido trench junction where the japan trench and the kurile trench intersect seismic coupling is deep and extends down to 52 55 km deep coupling was also found in the coquimbo region in central chile the mexico subduction zone has shallow coupling the transition occurs at 20 30 km depth previous studies of micro earthquakes in honshu hokkaido the aleutians and alaska show that earthquakes within the upper plate extend no deeper than the downdip edge of the coupled zone that we find given our measurements of seismic coupling depth we then explore the mechanism that may determine coupling depth the concept of critical temperature has been used to explain the depth of seismic coupling in other tectonic environments thus we first test whether a critical temperature can explain our results temperatures at the plate interface are dependent on many variables but two that are poorly determined are shear stress and radiogenic heat generation shear stress has been constrained by inversion of heat flow data assuming a crustal radiogenic heat production rate of 3 1 exp z 8 5 wm 3 and a constant coefficient of friction we find two critical temperatures of about 400 c and 550 c the lower critical temperature may be characteristic of regions with a relatively thick continental crust and the higher temperature of regions with a relatively thin continental crust on the other hand one single critical temperature of about 250 c can explain the coupling depths if shear stresses are constant with depth

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

oceanography the rossby rototiller planetary waves also known as rossby waves propagate throughout the world s oceans on very large scales they influence the ocean climate system and also it seems the delivery of nutrients to the ocean surface

iterative deconvolution of complex body waves from great earthquakes the tokachi oki earthquake of 1968 abstract a method of body wave inversion is developed in an attempt to extract the information about asperities or barriers in a fault zone a sequence of point sources each being characterized with the seismic moment the onset time and the location are iteratively derived from observed records at multi stations where the two dimensional extent of the source location is taken into account a modification is made of the iterative method of kikuchi and kanamori on the formulation of inversion procedure to facilitate the computation using this method we analyse long period p waves of the tokachi oki earthquake of 1968 mw 8 2 and obtain several significant subevents with time durations of 10 s their spatio temporal distribution shows that the rupture process consists of three characteristic stages a a stage of introductory rupture b a stage of main rupture and c a stage of aftershocks the main rupture takes place in the form of clustering around a few sites of the fault plane the largest subevent occurs in the northwestern corner the stress drop associated with this event is estimated to be 200 bars one order of magnitude higher than the stress drop averaged over the entire fault plane the sum of the seismic moments of the individual subevents amounts to 2 3 1028 dyn cm which approximately coincides with the one estimated from the analysis of long period surface waves this implies that the source of the tokachi oki earthquake consists of several major subevents with time durations of 10 s in addition to other minor subevents

loci and maximum size of thrust earthquakes and the mechanics of the shallow region of subduction zones earthquakes do not extend updip along the plate interface at most subduction zones all of the way to the plate boundary at the trench axis or deformation front rather the shallowest part of that interface moves mainly through stable aseismic slip that part of the plate boundary referred to here as the aseismic zone occurs along the base of an accreted wedge of young sediments the probable primary cause for the existence of this aseismic zone is the stable slip properties of the unconsolidated and semiconsolidated sediments in that zone subducted sediment is progressively dewatered and underplated to the base of the overriding plate through this process more consolidated rocks eventually come into contact at depth across both sides of the plate boundary from the point where sufficiently hard rock is found across the plate interface that interface will change its slip behavior to unstable stick slip sliding which is characteristic of consolidated material under most conditions this type of motion is accommodated seismically as episodic slip in large earthquakes the location of this transition to seismic behavior referred to as the seismic front marks the deep end of the aseismic zone and the top of the seismogenic zone i e that part of the plate interface that moves primarily in thrust earthquakes several convergent plate margins are discussed to illustrate the seismic front and the aseismic zone we find that the seismic front defined by smaller earthquakes that occur during the interval between large events is nearly the same as that for large events as inferred from the locations of their aftershocks the location of the seismic front is important for making estimates of the maximum possible size of thrust earthquakes along the plate boundary because it delimits the trenchward limit of the potential rupture area of these events the size of large thrust earthquakes is proportional to rupture area and to at least the cube of the downdip width w of that area thus by defining the location of the seismic front for convergent margins it is possible to make better estimates of w and hence to deduce the maximum size of future interplate earthquakes the average repeat time of such events is also related to w and so better estimates of average repeat time are possible from improved knowledge of w the hypothesis that the location of the seismic front is related to the maximum depth of subduction of unconsolidated sediment has implications for forearc mechanics we use a mechanical analysis laboratory modeling and multichannel seismic information to develop a simple model explaining the growth of forearcs the outer arc high or trench slope break that occurs arcward of most accretionary wedges represents an abrupt change in the critical taper of the accretionary wedge we argue that that change is caused by a large arcward increase in the strength of the material within the overriding plate that stronger material is called the backstop our laboratory modeling experiments indicate that a backstop with a trenchward dipping upper surface results in the development of an overlying structure that includes all of the primary morphologic features observed in modern forearcs in our modeling an accretionary wedge develops trenchward of the backstop an outer arc high develops above the trenchward toe of the backstop and farther arcward a passive forearc basin forms above the stronger material of the backstop this model is consistent with the observation that earthquakes do not extend updip along the plate interface all the way to the trench axis we hypothesize that plate motion is accommodated seismically along the base of the consolidated backstop and mostly or entirely aseismically trenchward of the toe of the backstop along the base of the accretionary wedge at several margins the seismic front is approximately coincident with the outer arc high supporting this interpretation

the interaction of a subducting lithospheric slab with a chemical or phase boundary we have used a finite element model of time dependent convection to determine the conditions for penetration of the subducted plate into the lower mantle a temperature dependent and non newtonian rheology is applied to achieve platelike behavior of the upper and sinking thermal boundary layer of convection the 650 km discontinuity is taken as either a chemical or phase boundary or as a combination of both it is represented by a marker chain which effects additional buoyancy when distorted out of its equilibrium position when the compositional density contrast is greater than about 5 the descending slab is deflected sidewards at the boundary and two layer convection prevails a resulting depression of the boundary in the range of 50 200 km should be detectable with seismic methods below 5 density difference the slab plunges several hundred kilometers into the lower mantle and below 2 it will probably not stop before reaching the core mantle boundary and extensive mixing would be expected with a pure phase change a negative clapeyron slope of about 6 mpa k 60 bar k is required to establish a type of leaky double layer convection a more moderate slope can aid a small compositional density difference to prevent slab penetration into the lower mantle with the present uncertainties about the physical nature of the 650 km discontinuity a variety of convective styles appears possible on dynamical grounds

the 1968 tokachi oki and the 1969 kurile islands earthquakes variability in the rupture process the may 16 1968 tokachi oki mw 8 2 and the august 11 1969 kurile islands mw 8 2 shallow thrust earthquakes occurred along the japan kurile arc about 500 km apart and possess similar static fault parameters their dynamic source processes were investigated using the observable directivity in the source time functions deconvolved from long period p waves the rupture processes of both earthquakes can be understood in terms of a combination of the end member asperity and barrier models of earthquake rupture the 1969 kurile islands earthquake ruptured in the sense of the asperity model one region of the fault plane radiated most of the seismic moment i e the asperity and is surrounded by the rupture zones of large precursor events the rupture process of the 1968 tokachi oki earthquake contains elements of both end member rupture models a dominant asperity is bounded to the south by a region of the fault plane ruptured by a large precursor event and is bounded to the north by a geometric barrier where the plate margin changes direction this geometric feature is responsible for the abrupt termination of the rupture front it appears that the tectonic setting plays a vital role in determining the rupture mode earthquakes that occur along linear trenches where no geometric or topographic complications exist seem to rupture in the sense of the asperity model whereas earthquakes that occur in the vicinity of such complications are more likely to possess rupture processes intermediate between the two end member models

tsunami generation by horizontal displacement of ocean bottom tsunami generation by an earthquake is generally modeled by water surface displacement identical to the vertical deformation of ocean bottom due to faulting the effect of horizontal deformation is usually neglected however when the tsunami source is on a steep slope and the horizontal displacement is large relative to the vertical displacement the effect becomes significant we show this for two recent earthquakes which generated much larger tsunamis than expected from seismic waves in the case of the 1994 june 2 java indonesia earthquake the focal mechanism was a very shallow dipping thrust and the source was near a very steep trench slope in the case of the 1994 nov 14 mindoro philippines earthquake strike slip faulting extended from ocean to land perpendicular to the coast line in both cases we found that the horizontal motion of slope had an important contribution to the tsunami generation

inversion of intermediate period rayleigh waves for source characteristics of the 1968 tokachi oki earthquake a least squares inversion technique was applied to rayleigh waves with periods of 10 25 s to determine the distribution of moment release within the source region of the 1968 tokachi oki earthquake the inversion procedure attempts to produce synthetic seismograms which match the data by solving for the amount of moment generated from each point of a grid spaced at 40 km the data were recorded on low gain mechanical seismometers that were located 70 200 km from the source region assuming simple unilateral and bilateral rupture models the inversion was run for different values of constant rupture velocity resulting in a best fit to the data at 3 0 3 1 km s for both models the calculated surface wave synthetics depended strongly on the crustal velocity model by using a velocity structure obtained from a refraction survey the waveforms of the synthetics became significantly different depending on whether we used discontinuities or linear gradients to connect the depth points for which the survey gives a refractor p velocity neither a structure of only discontinuities nor a structure of only gradients was found to produce satisfactory synthetics therefore an intermediate structure with a linear gradient near the surface and discontinuities below was used the results of the inversion show that the data can be modeled with a source consisting of two strong subevents which dominate the radiation of these surface waves the relative location of the two subevents is consistent with the locations of the two subevents of high stress drop that were seen on strong motion records

oceanic rossby waves acting as a hay rake for ecosystem floating by products recent satellite observations of rossby waves and chlorophyll anomalies propagating in subtropical gyres have suggested that wave induced upwelling could stimulate photosynthesis instead we show that chlorophyll maxima are located in abnormally warm water in rossby wave induced convergences this excludes inputs of nutrients from deeper water we argue that the sea color anomalies are not caused by chlorophyll but by floating particles evolved from the ecosystem and accumulated by rossby waves acting as marine hay rakes in convergence zones such processes may be determinant for the distribution of living organisms in oligotrophic areas

the sanriku oki japan earthquake of december 28 1994 mw 7 7 rupture of a different asperity from a previous earthquake fault geometry depth and slip distribution of the sanriku oki earthquake of december 28 1994 ms 7 5 are estimated from seismic waveforms geodetic measurements and tsunami waveforms and compared with those of the 1968 tokachi oki earthquake mw 8 2 the most recent large earthquake in the epicentral region seismic wave inversions indicate a shallowly dipping thrust type mechanism and the focal depth of 22 28 km representing an underthrust event at the subduction interface the source time function has an initial stage of 20 s followed by a main pulse of 30 s duration a shape similar to that of the 1968 tokachi oki earthquake joint inversion of geodetic and tsunami data shows that the region of the largest slip 1 7 m corresponds to a region of relatively small slip for the 1968 tokachi oki earthquake furthermore the joint inversion shows that the region of the largest asperity of the 1968 earthquake had essentially zero slip during the 1994 sanriku oki earthquake these results indicate that the dominant asperities ruptured by the 1994 sanriku and 1968 tokachi oki earthquakes are different the result of the joint inversion also shows that the aseismic zone near the japan trench was not ruptured by the 1994 earthquake