are the viking lander sites representative of the surface of mars abstract global remote sensing observations of mars are compared with remote sensing observations of the two viking lander site regions and with orbiter and lander imaging of the sites the lander sites do not fit most of the global trends of remote sensing data the presence of a duricrust in the top meter of the surface is inferred for most regions of high thermal inertia although the duricrust is thinner at the lander sites than elsewhere regions of low thermal inertia are covered by greater than several centimeters of unconsolidated dust a thin microns thick layer of bright dust appears at the surface at the lander sites and these locations may be regions of incipient formation of low thermal inertia the lander sites are intermediate in structure between classical bright and dark regions and are distinctive from most of the rest of the planet

source finiteness of large earthquakes measured from long period rayleigh waves the source finiteness parameters of 11 large shallow earthquakes were determined from long period rayleigh waves recorded by the global digital seismograph network and international deployment of accelerometers networks the basic data sets are the seismic spectra of periods from 150 to 300 s in the determination of source process times we used furumoto s phase method and a linear inversion method in which we simultaneously inverted the spectra and determined the source process time that minimizes the error in the inversion these two methods yielded consistent results the source process times of the sumbawa indonesia colombia ecuador valparaiso chile and michoacan mexico earthquakes were estimated to be 79 118 69 and 77 s respectively from the linear inversion method the source process times determined from long period surface waves were in general longer than those obtained from body waves source finiteness of large shallow earthquakes with rupture on a fault plane with a large aspect ratio was modeled with the source finiteness function introduced by ben menahem the spectra were inverted to find the extent and direction of the rupture of the earthquake that minimize the error in the inversion for a rupture velocity of 2 5 km s 1 the estimated rupture was unilateral 100 km long and along the strike n26 w for the may 26 1983 akita oki japan earthquake 165 km and s57 e for the september 19 1985 michoacan mexico earthquake 256 km and n31 e for the december 12 1979 colombia ecuador earthquake and 149 km and s15 w for the march 3 1985 valparaiso chile earthquake the results for the august 19 1977 sumbawa indonesia earthquake showed that the rupture was bilateral and in the direction n60 e these results are in general consistent with the rupture extent inferred from the aftershock area of these earthquakes

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

surficial properties in gale crater mars from mars odyssey themis data abstract we examine the nature of the surface layer in gale crater as determined from high resolution thermal and visible mars odyssey thermal emission imaging system themis data as well as how our conclusions compare to past analyses at themis resolution the thermal surface structure is dominated by local control thus providing us with detailed images that contain thermophysical information as well using these data sets we have created a map of the area defining units based primarily on their geomorphology as determined from the daytime thermal and visible images and then using the nighttime thermal data to interpret the nature of the surface layer within each unit seven units have been defined i partially blanketed knobby plateaus ii crater walls with terrain similar to that on the plateaus on the upper half and exposed rocky surfaces on the lower half iii v three floor units with varying combinations of bedrock and indurated and or particulate deposits vi sand sheets and vii a central mound consisting of indurated and or rocky material forming layers terraces and slides covered by particulate material that tapers in thickness downslope additionally dozens of channels have been observed on the crater walls and central mound the results indicate that aeolian processes have played a major role in shaping much of the present surface layer within gale and may still be active today because of the dramatic size and structure of gale the winds are most likely controlled by the local topography additionally the presence and frequency of channels within gale bolster hypotheses involving aqueous episodes in the history of the crater

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

thermally distinct ejecta blankets from martian craters utilizing the termoskan data set of the phobos 88 mission we have recognized a new feature on mars ejecta blanket distinct in the thermal infrared edith virtually all of the more than 100 features discovered in the termoskan data are located on the plains near valles marineris ediths have a startlingly clear dependence upon terrains of hesperian age implying a spatial or temporal dependence on hesperian terrains almost no thermally distinct ejecta blankets are associated with any of the thousands of craters within the data set that occur on the older noachian units ediths also do not appear on the portions of the younger tharsis amazonian units seen in the data the hesperian terrain dependence cannot be explained by either atmospheric or impactor variations noachian and hesperian terrains must have experienced identical atmospheric and impactor conditions during hesperian times thermally distinct ejecta blankets therefore reflect target material differences and or secondary modification processes not all lobate ejecta blankets are thermally distinct but all ediths correlated with visibly discernible ejecta blankets are associated with lobate ejecta blankets the boundaries of the thermally distinct areas usually follow closely the termini of the fluidized lobate ejecta blankets even when the ejecta blankets show a high degree of sinuosity thus the thermally distinct nature of ediths must be due to the primary ejecta formation process the coupling of these thermal anomalies to morphology is unlike most sharp martian inertia variations which are decoupled from observed surface morphology some thermally distinct ejecta blankets occur near otherwise similar craters that do not have thermally distinct ejecta blankets thus wind patterns or locally available aeolian material cannot provide a single overall explanation for the observed variations we compiled a data base of 110 edith and non edith craters ranging in diameter from 4 2 km to 90 6 km there are almost no correlations within the data base other than occurrence on hesperian terrains we postulate that most of the observed ediths are due to excavation of thermally distinctive noachian age material from beneath a relatively thin layer of younger more consolidated hesperian volcanic material the plausibility of this theory is supported by much geological evidence for relatively thin near surface hesperian deposits overlying massive noachian megabreccias on the edith rich plains units we suggest that absence of thermally distinct ejecta blankets on noachian and amazonian terrains is due to absences of distinctive near surface layering thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth

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

hydrogeologic evolution of gale crater and its relevance to the exobiological exploration of mars abstract the presence of an amazonian impact crater lake in the noachian crater gale located in the aeolis northwest subquadrangle of mars is indicated by evidence from young floor deposits streamlined terraces layers and channels observed on the central sedimentary deposit evidence for the filling of this lake by two processes is described a the drainage of the aquifer in the aeolis mensae region supported by extended mass wasting and rim sliding in the crater at the contact with the mensae and b the overspilling of the northern rim by an amazonian south transgression of the elysium basin this last hypothesis is supported by hydrologic features such as channels and channel like depressions north of the crater and by the crescent like shape of the central sedimentary deposit the presence of an impact melt sheet and uplifted central peak may have also generated hydrothermal activity including an early crater lake shortly after the formation of the crater in the noachian period with time decreasing heat flux and changing climates gale may have experienced transitions in aqueous environments from warm and wet to cold and ice covered water that could have provided suitable oases for various communities of microorganisms preservation of the biological and climatic record may have been favored in this paleolacustrine environment which probably occured episodically over two billion years

thermal inertia of crater related wind streaks on mars data from the thermal emission spectrometer tes on board the mars global surveyor spacecraft are used to analyze the structure of and materials comprising crater related wind streaks comparisons of high resolution tes albedo and tes based thermal inertia values within and adjacent to the streaks allow us to constrain the properties of the streaks and gain insight into their physical structure the majority of the analyzed type i bright depositional streaks are distinct from the surrounding terrain in albedo but not in thermal inertia we conclude that these streaks consist of thin deposits of bright material greater than 1 pm thick but less than 1 3 mm thick the majority of the analyzed type i dark erosional streaks identified from viking images are now indistinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks have been covered by a thin deposit of bright material greater than 1 m thick but less than 1 3 mm thick all of the analyzed type ii dark depositional streaks are distinct from the surrounding terrain in both albedo and thermal inertia we conclude that these streaks consist of deposits greater than a few centimeters thick in this case we were also able to use the thermal inertia values to estimate the particle sizes of the deposited material the values correspond to a broad range of sand sized particles easily mobilized by wind supporting the deflation deposition theory of type ii streak formation

surface characteristics and degradational history of debris aprons in the tempe terra mareotis fossae region of mars abstract we have documented the surface characteristics and degradational history of a population of 65 lobate debris aprons in the tempe terra mareotis fossae region of mars these aprons were compared to other martian debris aprons to evaluate similarities and differences among different populations which can provide insight into the dominant controls on apron development tempe mareotis debris aprons found at the bases of isolated or clustered massifs escarpments and crater interior walls were studied using viking orbiter mars global surveyor and mars odyssey datasets in a gis database six textures related to degradation of apron surfaces are identified in moc images and they are divided into two groups an upper surface group and a lower surface group degradation occurs within an inferred smooth upper surface mantle of ice and debris producing a sequence of pitted ridge and valley and knobby textures of the upper surface group where upper surface materials have been removed smooth and ridged textures of the lower surface group are exposed degradation to various depths may expose lower surface materials which may consist of the main apron mass remnants of mantling deposits or both a combination of geologic processes may have caused the degradation including ice sublimation ice melt and eolian activity apron surfaces have lower maximum thermal inertias and mean surface temperatures than adjacent plains surfaces which may be explained by the trapping of unconsolidated materials in low lying pits and valleys formed by surface degradation or from the disruption of crusts on degraded portions of apron surfaces one feature observed only on tempe mareotis debris aprons are broad ridges which mimic the shape of massif bases for tens of kilometers we propose these to be constructional features that could have formed during cycles of increased debris production apron morphometric parameters including area volume slope thickness relief and h l were compiled and the results show that tempe mareotis aprons have average surface areas volumes and frontal thicknesses that are 2 3 times smaller than eastern hellas aprons within the tempe mareotis population escarpment related aprons are larger than massif related aprons suggesting that aprons with larger source areas have potentially greater volatile accumulation translating into longer apron travel distances and lower h l values

measurement of mantle wave velocities and inversion for lateral heterogeneity and anisotropy 1 analysis of great circle phase velocities long period 100 330 s fundamental mode love and rayleigh waves have been processed to measure the great circle phase velocities for about 200 and 250 paths respectively the observations are inverted for regionalized phase velocities and for an even order harmonic expansion of the lateral velocity heterogeneity the regionalized inversions achieve a maximum variance reduction of about 65 and 85 for the love and the rayleigh wave data respectively the l max 2 inversions give a maximum variance reduction of about 60 and 90 for love and rayleigh waves respectively the l max 8 inversion does not make a large improvement in the fit the love wave phase velocities have more power in l 4 and 6 relative to l 2 than the rayleigh waves for both love and rayleigh wave data the sectoral component dominates the l 2 harmonics and this component is stable if we increase l max from 2 to 6 heat flow also has strong sectoral components lm 22 which are approximately in phase with those of the phase velocities the l 2 harmonics of the nonhydrostatic geoid are dominated by large zonal lm 20 and moderate sectoral components the sectoral components are in phase with those of the phase velocities the sectoral pattern of heat flow and phase velocity is controlled by high heat flow low velocity of the east pacific rise and western north america which is reinforced by low velocities in the antipodal region red sea gulf of aden east african rift by contrast the geoid l 2 pattern is dominated by geoid highs over the western pacific subduction zones a spherical harmonic expansion of regionalized phase velocities shows that they have l 2 variations similar to those of the l max 2 nonregionalized inversions this means that the regionalization approach is appropriate as a first step for studying lateral heterogeneity of the earth however the great circle phase velocities are not sufficient by themselves to uniquely locate the lateral heterogeneity the same is true for free oscillation data regions of convergence have the interesting property of being slow for short period waves and fast faster than shields for long period waves

thermal inertia mapping of mars from 60 s to 60 n twenty micrometer brightness temperatures are used to derive the thermal inertia for 81 of the martian surface between latitudes 60 these data were acquired by the two viking infrared thermal mappers in 1977 and 1978 following the two global dust storms of 1977 the spatial resolution used is 2 in latitude by 2 in longitude and the total range in derived inertia is 1 to 15 10 3 cal cm 2 sec 12 k 1 the distribution of thermal inertia is strongly bimodal with all values of thermal inertia less than 4 10 3 cal cm 2 sec 12 k 1 being associated with three disjoint bright regions mostly in the northern hemisphere sufficient dust is raised in global storms to provide fine material adequate to produce these low inertia areas but the specific deposition mechanism has not been defined at the low resolution used no complete exposures of clean rock were found there is some tendency for darker material to be associated with higher thermal inertia although the trend is far from one to one the distribution of high and low inertia areas is sufficiently nonrandom to produce a variation in whole disk brightness temperature with central meridian longitude this variation and the change in surface kinetic temperature associated with dust storms are factors in establishing the whole disk brightness temperature at radio and infrared wavelengths and will be important for those who use mars as a calibration source

sedimentary features of seismoturbidites triggered by the 1983 and older historical earthquakes in the eastern margin of the japan sea abstract both mass failure deposits and turbidites are widely distributed in the epicentral area of the 1983 earthquake mw 7 9 in the eastern margin of the japan sea this basin is semi enclosed with no active conduits for the entrance of coarse detrital sediments seismic reflection surveys and sediment cores reveal that mass failure deposits which are distributed on the continental slopes merge into turbidites in the basin plain hence the mass wasting process is a major transportation process in this region one gravity core gh93 816 was recovered from the southeastern margin of the japan basin close to the epicentral area of the 1983 japan sea earthquake sedimentological results show that five turbidite beds are intercalated in the top 68 cm of the column occurrence of the b tm tephra at the depth of 68 71 cm indicates that these turbidite beds were developed during the last 1000 years the high 137cs concentration in the top 20 cm of the core implies that the uppermost turbidite bed was deposited after 1954 based on these age limits for the top and the bottom of the studied interval we estimate the recurrence intervals of turbidites as 160 330 years we suggest that these turbidites were generated by submarine slides which were triggered by the 1983 and older historical earthquakes in this region these seismoturbidites are characterized by amalgamated beds irregular structure sequences grain size breaks fluctuations abrupt changes in composition within bed and variable composition among beds from these features we infer that deposition resulted from a series of turbidity currents associated with multiple or line sources for example multiple shallow slides that were regionally initiated by the same earthquake the sedimentary features described herein may be useful as criteria for identifying modern seismoturbidites in other settings as well as seismoturbidites in the geologic record however further study is needed for the distinction of this type of turbidites from other types e g tempestites reflected turbidites

can the okhotsk plate be discriminated from the north american plate the plate geometry in northeast asia has been a long standing question with a major issue being whether the sea of okhotsk and northern japanese islands are better regarded as part of the north american plate or as a separate okhotsk plate this question has been difficult to resolve because earthquake slip vectors along the kuril and japan trenches are consistent with either pacific north america or pacific okhotsk plate motion to circumvent this difficulty we also use slip vectors of earthquakes along sakhalin island and the eastern margin of the japan sea and compare them to the predicted eurasia okhotsk and eurasia north america motions for a model with a separate okhotsk plate we invert 10 eurasia okhotsk and 255 pacific okhotsk slip vectors with pacific north america and eurasia north america nuvel 1 data alternatively for a model without an okhotsk plate those eurasia okhotsk and pacific okhotsk data are regarded as eurasia north america and pacific north america data respectively the model with an okhotsk plate fits the data better than one in which this region is treated as part of the north american plate because the improved fit exceeds that expected purely from the additional plate the data indicate that the okhotsk plate can be resolved from the north american plate the motions on the okhotsk plate s boundaries predicted by the best fitting euler vectors are generally consistent with the recent tectonics the eurasia okhotsk pole is located at northernmost sakhalin island and predicts right lateral strike slip motion on the nne striking fault plane of the may 27 1995 neftegorsk earthquake consistent with the centroid moment tensor focal mechanism and the surface faulting along the northern boundary of the okhotsk plate the north america okhotsk euler vector predicts left lateral strike slip consistent with the observed focal mechanisms on the nw boundary of the okhotsk plate the eurasia okhotsk euler vector predicts e w extension discordant with the limited focal mechanisms and geological data this misfit may imply that another plate is necessary west of the magadan region in southeast siberia but this possibility is hard to confirm without further data such as might be obtained from space based geodesy

high resolution thermal inertia mapping from the mars global surveyor thermal emission spectrometer abstract high resolution thermal inertia mapping results are presented derived from mars global surveyor mgs thermal emission spectrometer tes observations of the surface temperature of mars obtained during the early portion of the mgs mapping mission thermal inertia is the key property controlling the diurnal surface temperature variations and is dependent on the physical character of the top few centimeters of the surface it represents a complex combination of particle size rock abundance exposures of bedrock and degree of induration in this work we describe the derivation of thermal inertia from tes data present global scale analysis and place these results into context with earlier work a global map of nighttime thermal bolometer based thermal inertia is presented at 1 4 per pixel resolution with approximately 63 coverage between 50 s and 70 n latitude global analysis shows a similar pattern of high and low thermal inertia as seen in previous viking low resolution mapping significantly more detail is present in the high resolution tes thermal inertia this detail represents horizontal small scale variability in the nature of the surface correlation with albedo indicates the presence of a previously undiscovered surface unit of moderate to high thermal inertia and intermediate albedo this new unit has a modal peak thermal inertia of 180 250 j m 2 k 1 s 1 2 and a narrow range of albedo near 0 24 the unit covering a significant fraction of the surface typically surrounds the low thermal inertia regions and may comprise a deposit of indurated fine material local 3 km resolution maps are also presented as examples of eolian fluvial and volcanic geology some impact crater rims and intracrater dunes show higher thermal inertias than the surrounding terrain thermal inertia of aeolian deposits such as intracrater dunes may be related to average particle size outflow channels and valleys consistently show higher thermal inertias than the surrounding terrain generally correlations between spatial variations in thermal inertia and geologic features suggest a relationship between the hundred meter scale morphology and the centimeter scale surface layer

seismicity before and after large shallow earthquakes around the japanese islands abstract by establishing the space time distribution of certain features of seismicity before and after large shallow earthquakes occurring mainly along the deep sea trenches around the japanese islands these earthquakes can be classified into three types a b and c in type a seismic activity in the focal region becomes very low prior to a large earthquake creating a seismic gap of the second kind in type b seismic activity gradually increases in and around the focal region before a large earthquake and in type c seismic activity increases steadily without a predominant principal earthquake ever occurring i e a swarm pattern occurs observation of the locations where these three types of earthquakes occur indicates a close relationship with submarine topography type a earthquakes occur where the submarine topography is quite simple type b earthquakes where it is complex such as in a subduction zone disturbed by oceanic ridges or active tectonic lines and type c where seamounts subduct beneath the continental plate at the deep sea trench creating a very complex submarine topography where the submarine topography in the focal region is simple and flat the earthquake fault surface may be relatively homogeneous whereas the submarine topography is more complex the fault itself is also more complex thus it is deduced that the differences in seismicity patterns between these three types is due to the irregularity of their faults and a hypothesis to explain the mechanism of these three patterns is proposed

mapping the upper mantle three dimensional modeling of earth structure by inversion of seismic waveforms a method is presented for the inversion of waveform data for the three dimensional distribution of seismic wave velocities the method is applied to data from the global digital networks international deployment of accelerometers global digital seismograph network the selected data set consists of some 2000 seismograms corresponding to 53 events and 870 paths the moment tensors of the earthquakes are determined through an iterative procedure which minimizes the corrupting influence of lateral heterogeneity a global model is constructed for shear wave velocity expanded up to degree and order 8 in spherical harmonics and described by a cubic polynomial in depth for the upper 670 km of the earth s mantle although no a priori information is incorporated the model predictions reproduce much of what is known about the dispersion of mantle waves for example high phase velocities for shields low velocities at ridges and a strong degree 2 pattern for rayleigh waves since the method makes use of complete waveforms overtone data are also included it is shown that the model is reproducible in that substantially the same model can be constructed from each half of the total data set considered independently the model shows that shields and ridges are major features in the depth interval 25 250 km the ridges of the southern pacific and the larger shields persist to 350 km but the southeast indian rise is underlain by a high velocity anomaly at this depth as is much of the mid atlantic ridge at 450 650 km the major features are a broad region of high velocities incorporating south america much of the south atlantic and parts of west africa a broad region of low velocities in the central and eastern pacific high velocities in the western pacific and a low velocity anomaly beneath the red sea and the gulf of aden in the absence of a crustal correction degrees 2 and 3 show a high positive correlation with the geoid paradoxically this is largely destroyed when the distribution in crustal thickness is taken into account spherical harmonic degrees 4 7 show a significant negative correlation

high resolution thermal inertia mapping of mars sites of exobiological interest we have mapped thermal inertia at high resolution for selected regions of mars that are of potential biological relevance using observations made by the mars global surveyor thermal emission spectrometer thermal inertia is a direct indicator of physical properties of the surface at the decimeter to meter scale our goal is to understand the geological processes by which the sites formed and their subsequent evolution their current state and their safety and science potential as landing sites for future lander rover and sample return spacecraft missions the thermal inertia values at 3 km scale for the sites considered span the entire range of values measured at mars thermal inertias range from low values indicative of substantial aeolian mantling up to high values suggesting surfaces covered predominantly with bedrock exposed rocks or blocks or well indurated crusts the highest thermal inertias correlate strongly with local morphology while areas with intermediate and low thermal inertias generally show no such correlation this suggests that selection of future landing sites will be plagued by a choice of a well mantled site that is safe but less interesting scientifically versus an unmantled site that is more interesting scientifically but less safe

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

fault related folds above the source fault of the 2004 mid niigata prefecture earthquake in a fold and thrust belt caused by basin inversion along the eastern margin of the japan sea 1 the 2004 mid niigata prefecture earthquake occurred in a fold and thrust belt that has been growing since late pliocene time in a miocene rift basin along the eastern margin of the japan sea we constructed the trajectory of the subsurface faults responsible for the growth of the folds from the geologic structure and stratigraphy in the source region assuming that the folds have been growing as fault related folds because of inclined antithetic shear with a dip of 85 in the hanging wall above a single reverse fault the fault trajectory constructed from the fold geometries nearly coincides with the geometries of the source fault of the main shock of the 2004 earthquake revealed by aftershocks which supports that the rupture was along a geologic fault that has ruptured repeatedly during the last a few million years a three dimensional fault model based on 12 fault trajectories constructed along parallel sections revealed that the main shock occurred on a convex bend in the fault surface and that the southern termination of the aftershock distribution nearly coincides with a concave bend in the fault the close relation between the source fault and the geologic structure shows that it is possible to construct source fault geometry assuming inclined shear as deformation mechanism of a hanging wall and to infer the rupture areas from geologic data

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

source mechanisms of twenty six large shallow earthquake ms 6 5 during 1980 from p wave first motion and long period rayleigh wave data source mechanisms of 26 large shallow earthquakes are determined in terms of a double couple point source with a correction for the nondirectional part of source finiteness by using p wave first motions and long period rayleigh wave spectra recorded on wwssn ida and gdsn networks the combined use of both data sets allows us to determine the double couple mechanism uniquely in most cases constrained linear moment tensor inversion m xz m yz 0 correctly determines the strike of the fault but fails to estimate the dip and underestimates the scalar moment all thrust events along the deep sea trenches analyzed in this study show nodal planes which dip perpendicular to the trench axis at an angle shallower than 45 the fit to data of the double couple inversion is comparable to that of the constrained moment tensor inversion using the phase spectra of surface waves we can detect a slow source process with an accuracy of about 10 to 20 sec

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

a new attenuation relation for peak horizontal acceleration of strong earthquake ground motion in japan abstract a new attenuation relation for peak horizontal acceleration applicable to the near source region in japan is developed the data base consists of 1372 horizontal components of peak ground acceleration from 28 earthquakes in japan and 15 earthquakes in the united states and other countries coefficients describing the decrease in acceleration with increasing distance found by most previous studies of japanese data are significantly smaller than those found by analyzing individual earthquakes this phenomenon is examined and found to result from use of general nonstratified multiple regression analyses the present analysis uses a two step stratified regression procedure and an attenuation model that accounts for geometrical spreading and anelastic attenuation but has magnitude independent shape at very short distances the resulting relation in japan is log 10 a 0 41 m log 10 r 0 032 10 0 41 m 0 0034 r 1 30 where a is the mean of the peak acceleration from two horizontal components at each site cm sec 2 r the shortest distance between site and fault rupture km and m the surface wave magnitude the median estimate of peak horizontal acceleration at the source region is 620 cm sec 2 independent of earthquake magnitude effects of four different ground condition rock hard medium and soft soils on the attenuation relation are also examined average peak horizontal accelerations for the rock and the soft soil sites are 60 and 140 per cent respectively of the value predicted from the equation

fault parameters and tsunami excitation of the may 13 1993 shumagin islands earthquake the shumagin islands earthquake of may 13 1993 occurred in a previously identified seismic gap where a large subduction earthquake is expected we analyzed long period surface waves and p waves recorded on the iris stations to estimate the fault parameters the centroid moment tensor solution shows that the focal mechanism is a thrust type with the strike parallel to the aleutian trench the seismic moment is 2 0 1019 nm and the corresponding moment magnitude is 6 8 the moment tensor rate function inversion from p waves also yields a similar focal mechanism and seismic moment in addition this computation provides estimates of 10 s for the duration of the source time function and 35 km for the best point source depth these seismological analyses indicate that the fault mechanism of the 1993 earthquake was as expected but that the magnitude was too small to fill the gap this earthquake did not generate a tsunami large enough to be observed at the sand point alaska tide gauge or at an ocean bottom pressure gauge at distances of 100 and 300 km respectively numerical tsunami simulations result in amplitudes at both stations that are within the background noise level additional numerical experiments also suggest that the small tsunami amplitudes are due to the location of the source area in the shallow shelf region

large earthquakes initiate by the acceleration of slips on the downward extensions of seismogenic faults abstract in order to examine the relationship between anomalous crustal deformations and subsequent large earthquakes we compiled and examined data on preseismic anomalous crustal deformations for two earthquakes that occurred in and around the japanese islands in recent years we found that the slip on a downward extension of a seismogenic fault accelerates before the main shock and that the average slip velocity is inversely proportional to the time remaining until the main shock occurs

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

surficial properties in melas chasma mars from mars odyssey themis data we examine the nature of the surface layer in a small area of the melas chasma region as determined from high resolution thermal and visible mars odyssey thermal emission imaging system themis data as well as how our conclusions compare to past analyses at themis resolution the thermal structure is dominated by local control and all significant thermal variations can be linked to morphology thus themis provides us with detailed images that contain thermophysical information as well allowing us to create a surficial geologic map intended to reflect the surface structure of the region eight units have been defined i blanketed plateaus with thermally distinct craters and fractures ii blanketed canyon walls with rocky edges iii indurated and or rocky canyon wall slide material partially covered by aeolian material iv an anomalous wall region with fluvial like depressions partially filled with particulate material v indurated and or rocky ridged and non ridged canyon floor landslide material mingled with aeolian material vi sand sheets vii indurated and or rocky rounded blocks intermingled with small areas of aeolian material and viii transverse dunes the themis thermal data support conclusions from previous studies but also reveal much more structure than was seen in the past we have found that all significant thermal variations in this region can be linked to morphology but all morphological variations cannot be linked to significant thermal variations themis visible images provide an intermediate resolution that bridges the gap between moc and viking and allow for a more meaningful interpretation of the geologic context of a region surfaces indicate that landslides were an important geologic process long ago shaping the canyon walls and floor while aeolian processes have subsequently altered the surface layer in many locations and may still be active

position of the disastrous 1999 puebla earthquake in the seismotectonic pattern of mexico the location of the 1999 puebla earthquake shows that this earthquake belongs to the class of disastrous intraplate earthquakes generated by fracturing of the continental lithosphere caused by the process of subduction this is obvious from the vertical section across the middle american wadati benioff zone and from its position in the revised seismically active los azufres rio salado fracture zone delineated in the continental lithosphere of the north american plate

the origin of the tsunami excited by the 1989 loma prieta earthquake faulting or slumping we investigated the tsunami recorded at monterey california during the 1989 loma prieta earthquake m w 6 9 the first arrival of the tsunami was about 10 min after the origin time of the earthquake using an elastic half space we computed vertical ground displacements for many different fault models for the loma prieta earthquake and used them as the initial condition for computation of tsunamis in monterey bay the synthetic tsunami computed for the uniform dislocation model determined from seismic data can explain the arrival time polarity and amplitude of the beginning of the tsunami however the period of the synthetic tsunami is too long compared with the observed we tested other fault models with more localized slip distribution none of the models could explain the observed period the residual waveform the observed minus the synthetic waveform begins as a downward motion at about 18 min after the origin time of the earthquake and could be interpreted as due to a secondary source near moss landing if the large scale slumping near moss landing suggested by an eyewitness observation occurred about 9 min after the origin time of the earthquake it could explain the residual waveform to account for the amplitude of the observed tsunami the volume of sediments involved in the slumping is approximately 0 013km 3 thus the most likely cause of the tsunami observed at monterey is the combination of the vertical uplift of the sea floor due to the main faulting and a large scale slumping near moss landing

the april 22 1991 valle de la estrella costa rica mw 7 7 earthquake and its tectonic implications a broadband seismic study the rapture process of a large back arc thrusting earthquake the april 22 1991 valle de la estrella costa rica mw 7 7 earthquake is investigated using broadband body waves and long period surface waves we find the source process to be relatively simple with the source models separately obtained from body and surface waves being very consistent the event occurred on a shallow southwest dipping rapture plane on which most energy is released updip of the hypocentral location 10 20 km deep high frequency radiation appears to have been released over a relatively small source area our preferred model has a focal mechanism with strike 102 10 dip 17 14 and rake 63 17 a seismic moment of 3 8 1 5 1020 n m and a total rupture duration of 40 6 s the earthquake appears to be associated with the north panama deformed belt npdb a thrust and fold complex that has accommodated the oroclinal deformation of panama this event along with previous large events north of panama in 1882 and 1916 indicates that there is substantial convergence along the npdb marking the npdb as a probable emerging plate boundary it remains difficult to gauge the earthquake hazard in the region because of the tectonic complexity

analytical model for gravity and rayleigh wave investigation in the layered ocean earth structure in terms of the linear theory of elasticity we analyze the gravity and rayleigh wave excitation and propagation process in a three layered ocean earth model which includes a superficial liquid layer and two layers of sediments soft and hard to compute the oceanic surface wave dispersion function the thomson haskell matrix method is used the solution is obtained by applying the normal mode formalism to the flat homogeneous layered ocean earth structure based on this theory the spectra of the excitation functions are investigated in detail for 45 thrust dip slip and strike slip point sources in the half space a numerical experiment reveals that the rigidity of the rock exerts a strong influence on both gravity and rayleigh waves in the case of rayleigh waves a layered structure of the bottom strongly affects the propagation process the main focus of the present study is to model tsunami and tsunamigenic events it is well known from observations that earthquakes that generate abnormally large tsunamis are mostly thrust events characterized by long source duration 2 4 times longer than typical earthquakes of similar moment and shallow source depth and are located near the trench axis meanwhile typical tsunamigenic earthquakes are generally dip slip and thrust events with depths between 15 and 50 km on this basis and using the distributed model of seismic source the influence of source mechanism location and source duration on the tsunami wave amplitude are investigated here the results of our model computations of the seismic sea waves from tsunami and tsunamigenic earthquake are in good agreement with real observation data

dip range for intracontinental reverse fault ruptures truth not stranger than friction abstract histograms of fault dips have been compiled for moderate to large m 5 5 reverse slip intracontinental earthquakes with the slip vector raking 90 30 in the fault plane the principal data set is restricted to earthquakes where the fault plane in the focal mechanism can be unambiguously distinguished from the auxilliary plane the reverse fault dips are bracketed within the range 12 1 the observed dip range is consistent with reactivation of faults possessing rock friction coefficients within byerlee9s 1978 range 0 85 s 0 6 undergoing frictional lockup at dips approaching 60 the broad 25 to 35 peak may arise from progressive domino steepening of imbricate reverse faults above the optimal dip for reactivation in regions undergoing bulk shortening paucity of very low angle thrusts implies that it is generally the steeper ramps within ramp flat assemblages that fail in moderate to large earthquakes the subsidiary peak at 45 to 55 likely results from compressional reactivation of former normal faults in areas undergoing tectonic inversion requiring some degree of fluid overpressuring the results are consistent with previous studies on the dip range for active normal faults that again demonstrate frictional lockup at reactivation angles approaching 60 together these analyses suggest that byerlee friction coefficients apply to faults with displacements of up to a few kilometers

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

scaling differences between large interplate and intraplate earthquakes a study of large intraplate earthquakes with well determined source parameters shows that these earthquakes obey a scaling law similar to large interplate earthquakes in which m 0 l 2 or u l where l is rupture length and u is slip in contrast to interplate earthquakes for which 1 10 5 for for the intraplate events 6 10 5 which implies that these earthquakes have stress drops about 6 times higher than interplate events this result is independent of focal mechanism type this implies that intraplate faults have a higher frictional strength than do plate boundaries and hence that faults are velocity or slip weakening in their behavior this factor may be important in producing the concentrated deformation that creates and maintains plate boundaries

detectability of very slow earthquake from tide gauge records a very slow earthquake or crustal deformation with a rise time longer than the period of the free oscillation of the earth is difficult to observe on seismograms however we show that it can be detected from tide gauge records because the free oscillation of an ocean basin such as the japan sea contains longer eigenperiods than those of the solid earth actually such an oscillation was excited by the niigata earthquake of 1964 and recorded on tide gauges comparison of the tide gauge spectra of the free oscillation with the noise spectra shows that the free oscillation of the japan sea excited by a magnitude 7 class earthquake can be detected in the present tide gauge observation system further a simulation for a very slow earthquake with a source process time of 1 hour shows that the slow event which cannot be detected on seismograms is detectable on tide gauges however the smaller the slip the more difficult it is to detect the movement because of the limited dynamic range of the existing tide gauge system if a slow deformation precedes a large earthquake tide gauge records would be useful for earthquake prediction so improvements in the observation system are desirable

effects of lateral heterogeneity and source process time on the linear moment tensor inversion of long period rayleigh waves spectra of mantle rayleigh waves recorded on the ida network are inverted to determine the seismic moment tensor of the 9 june 1980 california mexico border earthquake the 29 july 1980 vanuatu islands earthquake and the 9 july 1980 santa cruz islands earthquake examinations are made to correct for phase velocity lateral heterogeneity and source process time a simple regionalization stable continent tectonic region young ocean and old ocean improves results of the linear inversion but the phase correction is not large enough and the discontinuous change of phase velocity across the boundary between regions causes an artificial rapid change in apparent phase velocity as a function of azimuth therefore a more detailed but gradual representation of the lateral heterogeneity is desirable to correct for the propagation effect in the linear inversion a source process time which consists of the nondirectional part of the apparent duration of main faulting and the delay time of the faulting from initial break is estimated by a phase analysis of rayleigh waves the source process time is generally proportional to the seismic moment on the log log scale but some earthquakes deviate considerably from the general relation therefore the measurement of the source process time should be made before the moment tensor inversion the phase errors introduced by the lateral heterogeneity and source process time may cause a bias to low scalar moment

surficial geologic surveys of gale crater and melas chasma mars integration of remote sensing data abstract remote sensing observations of gale crater and melas chasma are synthesized to better understand the present surface layer in these two scientifically interesting regions data sets analyzed include geologic maps mars orbiter laser altimeter mola elevation thermal emission spectrometer tes albedo tes thermal inertia mola residual pulse width tes rock abundance and viking and mars orbiter camera images using these data sets we constrain the properties of and processes acting on the present surface and create self consistent models for the surface layer surface properties within gale crater are variable and complex and interpreting the surface layer is not straightforward observations indicate that aeolian processes have shaped some of the intracrater surface but other areas do not comply with this model and have counterintuitive surface characteristics in contrast aeolian activity appears to have played a large role in shaping the present day physical structure of all surfaces in melas chasma and is reflected in the remote sensing data sets here we summarize our analysis and discuss the surface attributes as determined from these data sets

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

the particle size of martian aeolian dunes the effective particle size of unconsolidated materials on the martian surface can be determined from thermal inertia due to a pore size dependence of thermal conductivity at martian atmospheric pressures because dunes consist of a narrow range of well sorted unconsolidated particles they provide for a test of the relationship between particle size and thermal inertia calculated from midinfrared emission data for the martian surface we use two independent approaches first thermal inertia data indicate that martian dunes have an average particle size of about 500 100 m or medium to coarse sand second we determine expected dune particle sizes from grain trajectory calculations and the particle size transition from suspension to saltation on earth the transition occurs for a grain when the ratio of the terminal fall velocity to the wind friction speed u t is near unity for grains at u t this occurs at about 52 m terrestrial dune sands have a mean of 250 m and are composed entirely of grains 52 m the corresponding martian transition grain size is about 210 m suggesting that martian dunes should be significantly coarser than terrestrial dunes grain saltation path length as a function of particle size also shows that under martian conditions larger grains than on earth will become suspended both approaches indicate that martian dune sand should be coarser than terrestrial dune sand thus while terrestrial dune grains are in the fine to medium sand range the average martian dune sediments are probably medium to coarse sands these results closely match the grain sizes determined from thermal inertia models providing the first direct test of the validity of these models for actual martian surface materials

the source fault of the 1983 nihonkai chubu earthquake revealed by seismic imaging abstract from 2011 to 2012 we conducted marine seismic surveys using a multichannel seismic reflection mcs system and ocean bottom seismometers obss in and around the hypocentral region of the 1983 nihonkai chubu earthquake the survey covered the area from the japan coast of the japan sea to the yamato basin and the japan basin we investigated the relationship between the nihonkai chubu earthquake and the crustal structure obtained from seismic reflection imaging and the p wave velocity structure near the hypocentral region the focus in the present paper is on seismic data that were acquired using both the mcs system and obss based on the results the crustal structure of the japan sea around the hypocentral region of the 1983 nihonkai chubu earthquake is divided into three types island arc crust thick oceanic crust and oceanic crust the nihonkai chubu earthquake occurred near the boundary between the thick oceanic crust and the island arc crust there is a strong possibility that the east dipping reflector detected in the crust was the source fault of the nihonkai chubu earthquake in addition the location of anticlines formed by the east dipping reverse fault occurring in the boundary of the crustal structure associated with the source fault of the nihonkai chubu earthquake was confirmed in the range of latitude from 39 20 to 41 15 n although they were not found south of this segment there is also a concentrated area of reverse faults and folds approximately 100 km west of the source region of the nihonkai chubu earthquake this area is located near the boundary between the thick oceanic crust and the oceanic crust

global omori law decay of triggered earthquakes large aftershocks outside the classical aftershock zone 1 triggered earthquakes can be large damaging and lethal as evidenced by the1999 shocks in turkey and the 2001 earthquakes in el salvador in this study earthquakes with ms 7 0 from the harvard centroid moment tensor cmt catalog are modeled as dislocations to calculate shear stress changes on subsequent earthquake rupture planes near enough to be affected about 61 of earthquakes that occurred near defined as having shear stress change 0 01 mpa the ms 7 0 shocks are associated with calculated shear stress increases while 39 are associated with shear stress decreases if earthquakes associated with calculated shear stress increases are interpreted as triggered then such events make up at least 8 of the cmt catalog globally these triggered earthquakes obey an omori law rate decay that lasts between 7 11 years after the main shock earthquakes associated with calculated shear stress increases occur at higher rates than background up to 240 km away from the main shock centroid omori s law is one of the few time predictable patterns evident in the global occurrence of earthquakes if large triggered earthquakes habitually obey omori s law then their hazard can be more readily assessed the characteristic rate change with time and spatial distribution can be used to rapidly assess the likelihood of triggered earthquakes following events of ms 7 0 i show an example application to the m 7 7 13 january 2001 el salvador earthquake where use of global statistics appears to provide a better rapid hazard estimate than coulomb stress change calculations

mechanics of back arc deformation in costa rica evidence from an aftershock study of the april 22 1991 valle de la estrella costa rica earthquake mw 7 7 the april 22 1991 mw 7 7 valle de la estrella costa rica earthquake represents back arc thrusting of the caribbean plate beneath the panama block along the north panama thrust belt large back arc thrusting events are quite rare occurring in only two other locations along the sunda arc and japan sea to better understand the mechanics of back arc thrusting we constrain the faulting geometry associated with the 1991 costa rica earthquake using aftershock locations and focal mechanisms obtained from a three component portable digital network deployed in and around the aftershock area following the mainshock the spatial distribution of aftershocks reveals a complicated faulting geometry in the rupture area focal mechanisms determined from inversion of p wave and tangentially and radially polarized s wave sh and sv respectively amplitudes recorded by this temporary network confirm fault complexity and indicate active thrust normal and strike slip faults in the back arc of costa rica most of the thrust events are confined to the southern portion of the aftershock zone in the vicinity of the mainshock their distribution suggests the existence of a near horizontal basal fault plane at a depth of about 15 km with many imbricate faults having steeper dips extending from the basal plane toward the surface events with strike slip mechanisms locate northwest of the thrust events and define a sw ne trending left lateral strike slip fault zone that represents the nw termination of the mainshock rupture and possibly the maximum nw extension of the panama block the superposition of the aftershock locations on a geologic map of the region shows that aftershocks are restricted to occur in the older more competent rock units volcanic and volcaniclastic rocks interbedded with carbonates of the back arc sedimentary basin shallow events depth 5 km occur only where these oldest units are exposed at the surface this suggests that 1 exposure of the lower units results from repeated earthquake slip on the shallow crustal faults imaged by the aftershocks and 2 as much as 7 km of basin fill material overlying the lower units northeast of the mainshock does not deform seismically but instead folds and possibly faults aseismically

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