tsunami generation of the 1993 hokkaido nansei oki earthquake heterogeneous fault motion of the 1993 hokkaido nansei oki earthquake is studied by using seismic geodetic and tsunami data and the tsunami generation from the fault model is examined seismological analyses indicate that the focal mechanism of the first 10 s when about a third of the total moment was released is different from the overall focal mechanism a joint inversion of geodetic data on okushiri island and the tide gauge records in japan and korea indicates that the largest slip about 6 m occurred in a small area just south of the epicenter this corresponds to the initial rupture on a fault plane dipping shallowly to the west the slip on the northernmost subfault which is dipping to the east is about 2 m while the slips on the southern subfaults which are steeply dipping to the west are more than 3 m tsunami heights around okushiri island are calculated from the heterogeneous fault model using different grid sizes computation on the smaller grids produces larger tsunami heights that are closer to the observed tsunami runup heights tsunami propagation in the nearly closed japan sea is examined as the free oscillation of the japan sea the excitation of the free oscillation by this earthquake is smaller than that by the 1964 niigata or 1983 japan sea earthquake

bottom response to a tsunami earthquake submersible observations in the epicenter area of the 1993 earthquake off southwestern hokkaido sea of japan we conducted a research campaign of nine dives using the manned submersible vehicle shinkai 6500 in 1995 beneath the central okushiri ridge along the eastern margin of the sea of japan the main objective was to investigate coseismic response and bottom disturbance to the tsunamigenic 1993 offshore southwestern hokkaido earthquake ms 7 8 42 47 n 139 12 e in the northern aftershock area including the mainshock epicenter the whole aftershock area occupies the western half of source area of the related tsunami between the okushiri ridge and the neighboring shiribeshi trough to the east we found a gentle scarplet of the earthquake fault that bounds the first terrace and a zone of open gashes on the flat terrace a number of sand blows open cracks and other slope failures occupied the slope of the okushiri ridge on the uplifted hanging wall side of the tsunami source area some fractures and holes whose activity had ceased soon after the earthquake began to be buried by the 2 year accumulation of recent sediments in contrast the shiribeshi trough on the footwall of the fault and in the subsided domain of the tsunami source area suffered no remarkable disturbance other than gentle folding our submersible observations elucidated the seafloor response to tsunamigenic uplift of the hanging wall of a seismogenic thrust fault which displays the present time section of back thrusting with an embryonic subduction along the eastern margin of the sea of japan

the genesis of the silica sands of black river st elizabeth jamaica the only reported occurrence of quartz rich sands in jamaica is on the plains of black river st elizabeth where they outcrop in isolated pockets the sands overlie limestones of the white limestone supergroup and the coastal group and partly underlie holocene peat deposits monocrystalline quartz containing fluid and mineral inclusions is the dominant mineral of the sands with the heavy minerals magnetite haematite epidote rutile anatase zircon and tourmaline occurring in minor amounts grain surface texture studies of the quartz grains have identified a series of mechanical and chemical features microtextures depicting marine aeolian and pedological environments have been retained on the grains and represent the last three stages in the history of the grains the petrography of the sands indicates an igneous provenance with the major source of the detrital minerals being the cretaceous granitoids that outcrop in the eastern half of the island these rocks were unroofed during the uplift of jamaica in the late tertiary and were subjected to extensive chemical weathering which accounted for the breakdown of the majority of their primary silicate minerals fluvial transportation and deposition of detritus onto the shelf of the south coast commenced during this period and continued into the pleistocene providing terrigenous sand that was modified along the coast to quartz arenite by moderate to high energy marine conditions tidal currents east west longshore currents and weathering contributed to the maturity of the sand by the time it had been transported along the shelf to the vicinity of black river during low sea level stands in the pleistocene some of this sediment that became trapped on the shelf was blown inland by south east winds

total analysis of the 1993 hokkaido nansei oki earthquake using seismic wave tsunami and geodetic data the fault geometry and slip distribution of the hokkaido nansei oki japan earthquake of july 12 1993 are estimated using seismic wave tsunami and geodetic data the moment tensor rate function inversion from p waves shows one nodal plane shallowly dipping to the west and the other nodal plane steeply dipping to the east the best depth is estimated as 10 15 km the source time history consists of an initial pulse with a duration of 10 s and moment release of 2 1020 nm followed by a complex rupture for at least 40 s the centroid moment tensor cmt solution shows one nodal plane shallowly dipping to the east and the other steeply dipping to the west the overall seismic moment is estimated as 5 5 1020 nm mw 7 8 the joint inversion of geodetic data on okushiri island and tsunami waveforms in japan and korea shows that the largest slip about 6 m occurred at a small area just south of the epicenter this corresponds to the initial rupture on a fault plane dipping shallowly to the west the slip on the northernmost fault dipping to the east is about 2 m the slips on the southern faults dipping steeply to the west are more than 3 m total seismic moment of 4 9 1020 nm estimated from the slip distribution is similar to the estimate from cmt inversion

quantification of major earthquake tsunamis of the japan sea abstract the size of major tsunamigenic earthquakes which occurred in the japan sea is quantified on the basis of seismic and tsunamigenic source parameters the tsunami magnitude mt is determined from the instrumental tsunami wave amplitudes the mt values thus obtained are on average 0 2 units larger than the values of moment magnitude mw though the mt scale has originally been adjusted to agree with mw moreover the volume of displaced water at the source is on average 2 3 times as large as that for the pacific events with a comparable mw nevertheless the observed height of the sea level disturbance at the source is found consistent with the amount of crustal deformation computed for the seismic fault models these results indicate that the tsunami source potential itself is large for mw in comparison with the pacific events the large source potential is explained in terms of the effective difference both in the rigidity of the source medium and in the geometry of the fault motion for the japan sea events the mt scale still provides the physical measure of the tsunami potential and mt minus 0 2 corresponds to mw this predicts that the maximum amplitude of tsunami waves from japan sea earthquakes is at least two times as large as that from pacific earthquakes with a comparable mw

free oscillation of the japan sea excited by earthquakes ii modal approach and synthetic tsunamis summary the free oscillations of the japan sea excited by the 1964 niigata and the 1983 japan sea earthquakes are examined adopting a modal approach normal mode solutions with periods longer than 50 min are obtained numerically for the actual bathymetry provided by the grids of 20km in size the eigenvectors or water height distributions obtained show that the modes with longest eigenperiods are determined by the size and depth of the whole japan sea many modes with shorter eigenperiods are regionally trapped in a shallow part such as the continental shelf where the amplitude of eigenvectors is large the niigata earthquake excites mainly the regional modes whereas the japan sea event excites both kinds of modes equally the difference in excitation is attributed to the different water depth at the source the niigata earthquake occurred on a continental shelf about 100 m deep whereas the depth at the source area of the japan sea event is about 2500 m the synthetic tsunami is computed by a superposition of the normal modes the spectra agree well with those observed in the period range of 50 to 210 min

quartz microtextures and microstructures owing to deformation of glaciolacustrine sediments in the northern venezuelan andes glaciolacustrine sediments ranging in age from early to late merida wisconsinan in sections in the northern venezuelan andes near pedregal were studied to assess the effect of small scale folding and faulting on the surface microtextures of individual grains at site ped5 faulting of sediments beneath 35 m of middle to late merida glaciolacustrine glaciofluvial and probable till deposits has resulted in a maximum displacement of 1 m and many crushed sand grains are found along the shear zone these dominantly quartz particles are typically smoothed and or faceted with surface skins split from parent grains to produce adhering blade or wafer shaped coarse silts faulting with displacement of 40 cm occurs in late merida glaciolacustrine beds at sites ped13 and ped11 beneath ca 1 5 m of sediment and is thought to result from the removal of lateral support during valley erosion and possibly seismic disturbance associated sediments exhibit a greater incidence of small scale fold structures and convoluted bedding but with similar numbers and types of crushed grains all of the fault traces examined exhibit microstructural modifications including microfaulting folding and multiple domains associated with fluidisation and liquefaction the microtextures described are distinct from those produced by glacial or glaciofluvial transport processes and potentially may be used to infer glaciotectonic or other post depositional disturbance of sediments rare euhedral quartz grains with distorted crystallographic axes may derive from the shear zone of the regional trans form boconofault although many of these grains appear to be overprinted by glacial and or recent deformation processes copyright 2004 john wiley sons ltd

big mantle wedge anisotropy slabs and earthquakes beneath the japan sea abstract the japan sea is a part of the western pacific trench arc backarc system and has a complex bathymetry and intense seismic activities in the crust and upper mantle local seismic tomography revealed strong lateral heterogeneities in the crust and uppermost mantle beneath the eastern margin of the japan sea which was determined using p and s wave arrival times of suboceanic earthquakes relocated precisely with sp depth phases ambient noise tomography revealed a thin crust and a thin lithosphere beneath the japan sea and significant low velocity low v anomalies in the shallow mantle beneath the western and eastern margins of the japan sea observations with ocean bottom seismometers and electromagnetometers revealed low v and high conductivity anomalies at depths of 200 300 km in the big mantle wedge bmw above the subducting pacific slab and the anomalies are connected with the low v zone in the normal mantle wedge beneath ne japan suggesting that both shallow and deep slab dehydrations occur and contribute to the arc and back arc magmatism the pacific slab has a simple geometry beneath the japan sea and earthquakes occur actively in the slab down to a depth of 600 km beneath the ne asian margin teleseismic p and s wave tomography has revealed that the philippine sea plate has subducted aseismically down to the mantle transition zone mtz 410 660 km depths beneath the southern japan sea and the tsushima strait and a slab window is revealed within the aseismic philippine sea slab seismic anisotropy tomography revealed a nw se fast velocity direction in the bmw which reflects corner flows induced by the fast deep subduction of the pacific slab large deep earthquakes m 7 0 depth 500 km occur frequently beneath the japan sea western margin which may be related to the formation of the changbai and ulleung intraplate volcanoes a metastable olivine wedge is revealed within the cold core of the pacific slab at the mtz depth which may be related to the deep seismicity however many of these results are still preliminary due to the lack of seismic stations in the japan sea the key to resolving these critical geoscientific issues is seismic instrumentation in the japan sea for which international cooperation of geoscience communities in the east asian countries is necessary

magnitudes of large shallow earthquakes from 1904 to 1980 abstract in order to obtain a uniform magnitude catalogue surface wave magnitudes ms and broad band body wave magnitudes mb have been determined for large shallow earthquakes from 1904 to 1980 in making the catalogue homogeneous the author consistently adheres to the original definitions of ms and mb given by gutenberg 1945 and gutenberg and richter 1956 the determinations of ms and mb are all based on the amplitude and period data listed in gutenberg and richter s unpublished notes bulletins from stations worldwide and other basic information mb is measured on broad band instruments in periods of 8 s consistency of the magnitude determinations from these different sources is carefully checked in detail more than 900 shallow shocks of magnitude 7 and over are catalogued the meaning of the magnitude scales in various catalogues is examined in terms of ms and mb most of the magnitudes listed by gutenberg and richter 1954 in their seismicity of the earth are basically ms for large shocks shallower than 40 km but are basically mb for large shocks at depths of 40 60 km the surface wave magnitudes given by earthquake data reports are higher than ms by 0 2 unit whether the combined horizontal amplitude or the vertical amplitude is used mb and the currently used 1 s body wave magnitude are measured at different periods and should not be directly compared

a comparative sem study on the micromorphology of glacial and nonglacial clasts with varying age and lithology preliminary research on striated clasts from a variety of depositional environments suggests that scanning electron microscopy sem of striated clasts of varying lithology in diamictons may prove useful in interpreting a glacial origin evaluating whether sem analysis of clasts from diamictons is an applicable technique to define a glacial origin requires a better understanding of the microfeatures occurring on glacial and nonglacial clasts we describe microtextures and surface characteristics for samples of quartzite granite limestone basalt chert pillow basalt and quartz pebbles collected from a variety of depositional environments our study suggests that it is possible to differentiate between glacial and nonglacial deposits based on frequency and morphology of diagnostic surface microfeatures observed on entrained clasts these microfeatures are best preserved and identified on competent and monomineralic samples e g quartzite chert limestone and poorly preserved on less resistant and p

tsunamis caused by offshore active faults and their deposits abstract this paper reviews the variable features of coastal tsunamis caused by offshore active faults along the eastern margin of the japan sea emjs based on the historical records and modern observations of earthquakes and tsunamis tsunami deposits discovered along the emjs coast were also introduced and categorized depending on their sedimentary environments the offshore active faults which are densely distributed along the emjs and generate tsunamis are originated from the opening of the japan sea back arc basin during the late oligocene to miocene period the magnitudes of the earthquakes that caused large tsunamis in the emjs were under 8 0 the size of the fault plane approximately equal to the tsunami source area was approximately 10 100 and several tens of kilometers in length the slip distance of the reverse type faults was less than 20 m the sedimentary characteristics and depositional processes of tsunami deposits were obtained from deposits in various environments such as coastal lowlands marine terraces coastal lagoons and inland ponds certain unique approaches used to identify tsunami deposits were reviewed such as gravel layers that intercalate inorganic soils and a holocene marine terrace dinoflagellate cysts and foraminiferal linings which are potentially derived from the sea and chemical features e g the ca2 mg2 ratio as indicators of seawater inflow into a coastal lagoon the spatial distribution and recurrence of earthquakes and tsunamis in the emjs were found based on previous paleo tsunami studies the difference between tsunami deposits caused by offshore active faults and those by megathrust earthquakes only manifests itself in the horizontal and vertical directions but not in the sedimentary environments and structures the data thus inferred can be used for the estimation of offshore active fault models and validation of previous tsunami disaster reconstructions in the future

seismic imaging of the amur okhotsk plate boundary zone in the japan sea abstract we determined high resolution images of p and s wave velocity and poisson s ratio under the japan sea off honshu island using a large number of arrival time data from local earthquakes to understand the interaction of the amur and okhotsk plates our new data collected from the crustal earthquakes under the japan sea relocated precisely with sp depth phase are crucial to make this work possible our results show that strong lateral heterogeneities exist in the crust and upper mantle under the amur okhotsk plate boundary zone which may have affected the seismotectonics in the region the crustal velocity variations under the japan sea may reflect the complicated geologic structures that were produced during the opening of the japan sea and the present compressional stage of the honshu arc associated with the collision of the amur plate with the okhotsk plate low velocity zones in the mantle wedge are found to extend westward under the japan sea rather than just confined under honshu island suggesting that the back arc magmatism and tectonics are part of the complex geodynamic system in east asia

free oscillation of the japan sea excited by earthquakes i observation and wave theoretical approach summary tsunamis caused by the 1964 niigata and the 1983 japan sea earthquakes continued for a long time and appeared to have excited the free oscillation of the almost closed japan sea the spectral analysis of the tide gauge records of those tsunamis shows that there are distinct peaks above the noise level in the frequency range between 0 08 and 0 4mhz finitedifference computations of tsunami for the whole japan sea using a supercomputer reproduce those peaks and confirm that they represent the free oscillation of the japan sea the computation is also made for a region including only the se half of the japan sea with an artificial radiation condition on the n and w boundaries a comparison between the results of these two computations shows the effect of reflections from the nw coast and of the geometry and size of the whole japan sea the simulated spectrum from the se half region almost agrees with that from the whole japan sea for the niigata tsunami indicating that the niigata earthquake excites mainly the regional oscillations for the 1983 japan sea earthquake only a few peaks are reproduced by the computation for the se half region indicating that the free oscillation of the whole japan sea is the essential part of the spectrum for the japan sea event thus the excitation of the free oscillation depends on the earthquake location

the 12 july 1993 hokkaido nansei oki japan earthquake effects of source complexity on surface wave radiation abstract we present an analysis of the data dependency of surface wave inversions for source parameters of the 12 july 1993 hokkaido nansei oki japan earthquake this dependency is demonstrated by differences between source mechanisms obtained from different data sets particularly from rayleigh waves or love waves although inversions of various data sets yield unanimously thrust fault mechanisms for the inversion of rayleigh waves the mechanism is characterized by a shallow dipping west plunging nodal plane which is consistent with p wave first motion data and the distribution of aftershocks close to the hypocenter however for the inversion of both rayleigh and love waves the mechanism is characterized by a shallow dipping east plunging nodal plane several numerical experiments were carried out to test a hypothesis that the data dependency is attributed to the effects of source complexity on the surface wave radiation with the source complexity being characterized by tempo spatial changes in focal mechanism and moment release during the rupture process the experiments show that source parameters obtained from inversions of surface waves with periods as long as a few hundred seconds can be largely affected by using various models of source complexity proposed previously for the hokkaido earthquake and the effects on love waves tend to be systematically different from those on rayleigh waves our preferred source model is characterized by significant tempo spatial changes in focal mechanism the experiments based on this model provide a good explanation for the data dependency although our analysis cannot completely reject the alternative explanation that attributes the dependency to the manifestation of errors in modeling the surface wave propagation and or inversion instability the model is consistent with the data of body waves and long period surface waves for a very broad frequency band implying the existence of weak zones with various fault geometries along the eastern margin of the japan sea

the mechanism of the 1983 japan sea earthquake as inferred from long period surface waves and tsunamis abstract the source process of the japan sea earthquake of may 26 1983 is studied by using the long period surface waves and tsunamis the moment tensor inversion of rayleigh waves which consider the lateral heterogeneity of the earth is developed and applied to the ida records of this event the moment tensor solution and first motion data indicate that the mechanism is dip slip and the seismic moment is 7 6 1027 dyne cm the fault is estimated to be 120 km in length 40 km in width and dips eastward with a dip angle of 30 from the aftershock distribution tsunami simulation for an actual topography is made to restrain the slip on the fault the aftershock area and the tsunami records suggest that the fault is divided into two segments the northern part strikes nnw and slips 4 m while the southern part strikes nne and slips 5 m the fault geometry the aspect ratio and the stress drop of this event are similar to those of the 1964 niigata earthquake but differ from those of the earthquakes in the pacific coast of japan

re examination of the 1940 shakotan oki earthquake and the fault parameters of the earthquakes along the eastern margin of the japan sea abstract the fault model of the 1940 shakotan oki japan earthquake of aug 1 1940 is re examined on the basis of magnitude aftershock distribution and tsunami data from a careful examination of the s p time distribution of aftershocks and comparison of the tide gauge records with numerical simulation of tsunami the fault area is estimated to be 100 km 35 km the slip 1 5 m and the seismic moment 2 4 1027 dyn cm the fault parameters estimated in this study are significantly different from those of fukao and furumoto and do not support their conclusion that this event has a very long duration and is a tsunami earthquake the source process time is estimated to be 30 s which is normal for an earthquake of this size fault parameters of six earthquakes along the eastern margin of the japan sea including the shakotan oki event are compiled and compared with those of inter plate earthquakes in the pacific ocean different relations from well known scaling laws of the inter plate shocks are found for the earthquakes in the japan sea dip angles aspect ratios of the fault and the average stress drop are larger in the japan sea than those of the pacific events although the seismic moment release per unit fault length is the same the differences can be interpreted in terms of a recent plate boundary model in which the young immature boundary between the north american and the eurasian plates lies at the eastern margin of the japan sea they also partially reflect the different excitation of the tsunami in the japan sea and the pacific ocean

chattermark trails surface features on detrital quartz grains indicative of a tropical climate abstract with respect to weathering erosional processes and sediment transport quartz is one of the most stable minerals and makes up to 98 of the mineral volume of siliciclastic sands pettijohn et al 1987 although a major component in a wide variety of rocks quartz has almost no characteristic properties that allow determining parent rock types quartz does not contain characteristic cleavage planes and quartz grains react to impact or collision with other sediment particles by producing conchoidal fractures very similar to those observed for broken glass for sedimentologists physical geographers and soil scientists detrital quartz grains are poor in characteristic features except for a suite of surface features that may be indicative of various transport environments or even climate related alterations one of these surface features are chattermark trails chattermark trails are a series of linearly arranged rune like grooves on surfaces of minerals grains such as quartz and garnet lacking any type of cleavage these trails have been described from many unconsolidated sediments and are attributed mostly to glacial sediments laboratory experiments on polished quartz beads reveal that chattermark trails are not primary surface features but become visible after etching by dilute hydrofluoric acid comparison of the etched and non etched surface of the same quartz bead reveals that mechanically produced invisible cracks related to blunt collisions with other polished quartz beads became visible only after chemical etching chattermark trails on detrital quartz grains are the product of two processes the dynamic one is an invisible transport related blunt collision followed by a second stationary process which enables quartz dissolution to make the chattermarks visible in the broad field of laterite research it is well accepted that quartz dissolution in surface or near surface deposits is restricted to stationary chemical weathering in a wet tropical or at least subtropical climate drawing on this information chattermark trails are no longer considered a product of a specific sedimentary environment but reveal a distinct history of the quartz grain they are formed by blunt collisions in a sediment transport stage before experiencing some dissolution during a depositional stage in a tropical climate grains can be remobilized in an active sediment transport system collectively the results reveal that chattermark trails on quartz grains provide unique insights into the transport and climate history of sediments

an overview of the role of weathering in the production of quartz silt abstract quartz silt is a widespread detrital sediment with large aeolian loess and alluvial silt deposits forming important components of many contemporary landscapes despite research findings which indicate that a range of opportunities exist for the comminution of quartz into silt particles within a wide variety of geomorphic environments e g glacial grinding fluvial comminution aeolian abrasion frost weathering salt weathering insolation weathering and deep weathering the glacial aeolian hypothesis has traditionally been favoured as the most likely explanation for loess formation and loess is seen as primarily a quaternary phenomenon as a consequence there has been a tendency to underestimate sediment inputs into loess systems by geomorphological processes operating within pre quaternary environments in particular earth scientists may have considerably underestimated the role of weathering in global silt generation as there are now many references to the existence of a patchy but widespread distribution of pre quaternary weathering profiles across the glacial and periglacial landscapes of the northern hemisphere e g north america british isles north and central europe landscapes within which many of the classical loess deposits are located these observations suggest that weathering profiles may have covered large tracts of the northern hemisphere land surface prior to the quaternary glaciations this in turn may have important implications for quartz silt generation as 1 experimental studies indicate that many weathering processes are capable of generating significant quantities of silt sized debris and 2 particle characteristics displayed by saprolitic material that has developed on quartz rich crystalline source rocks often include significant quantities of either silt sized material or quartz grains that are weakened by weathering derived microfractures thus weathering profiles may represent mines of actual and potential quartz silt available for release into sedimentary systems when these profiles are subsequently reworked by geomorphological processes such as glacial fluvial and aeolian erosion

paleoseismology of deep sea faults based on marine surveys of northern okushiri ridge in the japan sea 1 the eastern margin of the japan sea is an incipient convergent margin characterized by distributed active faults and large scale earthquakes to evaluate the earthquake potential of the northern margin the source area of the 1940 shakotan hanto oki earthquake m7 5 was reexamined and the earthquake recurrence interval was estimated by combining bathymetric seismic and dive survey data with a tsunami simulation seismic profiling clarified that five anticlines have formed in and around this source area during the last 1 8 million years the balanced cross section of one anticline supports that thrust faults extend to the base of the upper brittle crust at about 11 km depth and total slip is about 850 m dive surveys identified fresh collapses along the forelimbs of two anticlines inversion of observed tsunami waveforms to estimate the slip distribution suggests that these two anticlines were the sources of the 1940 earthquake the other three anticlines may be seismic gaps the dive surveys collected debris layers possible records of paleoearthquakes in muddy sediments from the rate of muddy sediment deposition around the anticlines the minimum recurrence interval of earthquakes was estimated to be about 1100 years from structural modeling the average interval was about 6400 years assuming that fault slip started 1 8 million years ago and 3 m of slip occurred during each earthquake taking into account the above results and the instantaneous plate convergent rate between the okhotsk and amurian plates the recurrence interval was inferred to be 1100 to a few thousand years

backarc deformation along the eastern japan sea margin offshore northern honshu abstract the structural evolution of the eastern japan sea margin offshore northern honshu is discussed on the basis of single channel seismic profiles backarc structures evolved in response to late oligocene middle miocene extension which was generated at high angles to the arc trench system the evolution of a late miocene recent compressional plate tectonic regime resulted in widespread basement inversion the eastern japan sea margin is characterized by variable inverted half graben systems which are obliquely oriented to the island arc the area is underlain by three major structural blocks which are separated by a nw and a wnw trending structural discontinuity these blocks experienced a northward increase in extension the two southern blocks contain nne ne oriented reverse faults while the northern block is underlain by n nnw trending reverse faults the orientation and geometry of basement faults compares well with faults mapped onshore honshu the evaluation of the eastern japan sea margin can be explained by early miocene ese directed extension followed by a middle miocene sse directed extension pliocene recent east dipping reverse faults extend along the base of the continental slope and form a discontinuous thrust front which is characterized by minor fault offsets these reverse faults are locally associated with small active arc volcanoes

the july 12 1993 hokkaido nansei oki japan earthquake coseismic slip pattern from strong motion and teleseismic recordings we employ a finite fault inversion scheme to infer the distribution of coseismic slip for the july 12 1993 hokkaido nansei oki earthquake using strong ground motions recorded by the japan meteorological agency within 400 km of the epicenter and vertical p waveforms recorded by the global digital seismograph network at teleseismic distances the assumed fault geometry is based on the location of the aftershock zone and comprises two fault segments with different orientations a northern segment striking at n20 e with a 30 dip to the west and a southern segment with an n20 w strike for the southern segment we use both westerly and easterly dip directions to test thrust orientations previously proposed for this portion of the fault the variance reduction is greater using a shallow west dipping segment suggesting that the direction of dip did not change as the rupture propagated south from the hypocenter this indicates that the earthquake resulted from the shallow underthrusting of hokkaido beneath the sea of japan static vertical movements predicted by the corresponding distribution of fault slip are consistent with the general pattern of surface deformation observed following the earthquake fault rupture in the northern segment accounts for about 60 of the total p wave seismic moment of 3 4 1020 n m and includes a large circular slip zone 4 m peak near the earthquake hypocenter at depths between 10 and 25 km slip in the southern segment is also predominantly shallower than 25 km but the maximum coseismic displacements 2 0 2 5 m are observed at a depth of about 5 km this significant shallow slip in the southern portion of the rupture zone may have been responsible for the large tsunami that devastated the small offshore island of okushiri localized shallow faulting near the island however may require a steep westerly dip to reconcile the measured values of ground subsidence

effects of bathymetry on tsunami propagation application of ray tracing to tsunamis ray tracing of seismic surface waves is applied to tsunami propagation to examine bathymetric effect along its propagation path computations are made for trans pacific tsunamis and for near field tsunamis in the japan sea for tsunamis across the pacific ocean the comparison to a uniform ocean shows that focusing and defocusing due to bathymetry are significant for some combinations of source and receiver for example the refraction of rays is predominant at the east pacific rise for the tsunami from chile the tsunamis in the japan sea are strongly affected by the shallow yamato rise the predicted arrival time and amplitude distribution generally agree with the observations from an actual tsunami since the computation can be made very quickly the method is useful for preliminary analysis of tsunami propagation such as in an operational warning system or in the determination of computational area for finite difference computation

crustal structure beneath southern norway imaged by magnetotellurics abstract we use data from two magnetotelluric profiles tosca10 and tosca 09 over the scandinavian mountains to study the crustal structure in southern norway the profiles cross the major tectonic structures of the caledonian orogen as well as the western margin of the precambrian baltica dimensionality and strike analyses indicate generally 3 d behavior of the data however the majority of the used data distinguishes a preferable strike direction which is supported by the geology of the region hence we employ 2 d inversion and choose to invert the determinant of the impedance tensor to mitigate 3 d effects in the data on our 2 d models magnetotelluric data from both profiles are inverted using a damped least squares solution based on a singular value decomposition we improved the solution by defining the inverse model covariance matrix through gradient or laplacian smoothing operators the two dimensional inversion models of the tosca 09 and tosca 10 field data from southern norway derived from the damped least squares scheme with the laplacian inverse model covariance matrix are presented resistive rocks extending to the surface image the autochthonous southwest scandinavian domain and the allochthonous western gneiss region near surface conductors which are located between the resistive caledonian nappes and precambrian basement delineate highly conductive shallow sea sediments so called alum shales they exhibit a decollement along which the caledonian nappes were overthrust a deeper upper to mid crustal conducting layer in the southwest scandinavian domain may depict the remnants of closed ocean basins formed during the accretions and collisions of various sveconorwegian terranes in tosca 10 the caledonian nappes the conducting alum shales and the deeper conductor are terminated in the west by the faltungsgraben shear complex which represents a crustal scale boundary between the western gneiss region in the west and the southwest scandinavian domain in the east

historical tsunami records on russian island the sea of japan in this article we provide data evidencing tsunamis on russian island over the last 700 years reconstructions are developed based on the analyses of peat bog sections on the coast of spokoynaya bay including layers of tsunami sands ancient beach sands under peat were deposited during the final phase of transgression of the medieval warm period we used data on diatoms and benthic foraminifers to identify the marine origin of the sands the grain size compositions of the tsunami deposits were used to determine the sources of material carried by the tsunamis the chronology of historical tsunamis was determined based on the radiocarbon dating of the underlying organic deposits there was a stated difference between the deposition environments during tsunamis and large storms during the goni 2015 and lionrock 2016 typhoons tsunami deposits from 1983 and 1993 were found in the upper part of the sections the inundation of the 1993 tsunami did not exceed 20 m or a height of 0 5 m a m s l 0 3 above high tide the more intensive tsunami of 1983 had a run up of 0 65 m a m s l and penetrated inland from the shoreline up to 40 m sand layer of tsunami 1940 extend in land up to 50 m from the present shoreline evidence of six tsunamis was elicited from the peat bog sections the deposits of which are located 60 m from the modern coastal line the deposits of strong historic tsunamis in the japan sea region in 1833 1741 1614 or 1644 1448 the xiv xv century and 1341 were also identified on russian island their run ups and inundation distances were also determined the strong historic tsunamis appeared to be more intensive than those of the xx century and considering the sea level drop during the little ice age the inundation distances were as large as 250 m

source times and scaling relations of large earthquakes source time is a kinematic fault parameter corresponding to the duration of seismic source time functions and is accurately determined from phase spectra of long period surface waves source times are determined for 36 large earthquakes during the last three decades scaling relations among source times seismic moments and fault dimensions are derived seismic moment is proportional to the cube of source time and fault dimension is proportional to source time source times for low angle thrust earthquakes along deep sea trenches are found to be longer than those of other types such as intraplate shocks and deep shocks they are also significantly longer than the rupture times expected from a haskell model suggesting that generally there exists an introductory stage of faulting that precedes the main stage of the rupture propagation