constraints on the moho in japan and kamchatka abstract this review collects and systematizes in one place a variety of results which offer constraints on the depth and the nature of the moho beneath the kamchatka peninsula and the islands of japan we also include studies of the izu bonin volcanic arc all results have already been published separately in a variety of venues and the primary goal of the present review is to describe them in the same language and in comparable terms for both regions we include studies using artificial and natural seismic sources such as refraction and reflection profiling detection and interpretation of converted mode body waves receiver functions surface wave dispersion studies in kamchatka and tomographic imaging in japan the amount of work done in japan is significantly larger than in kamchatka and resulting constraints on the properties of the crust and the uppermost mantle are more detailed japan and kamchatka display a number of similarities in their crustal structure most notably the average crustal thickness in excess of 30 km typical of continental regions and the generally gradational nature of the crust mantle transition where volcanic arcs are presently active

recognition of a locked state in plate subduction from microearthquake seismicity a tectonic state of a locked subduction is considered to be a possible source of a future interplate earthquake discriminating an actually locked state to verify its extent is therefore essential in constructing an accurate prospect against the forthcoming earthquake micorearthquake seismicity is an effective tool for such an analysis because it is considered to be a faithful indicator of the stress state and is expected to exhibit a characteristic pattern in the area where the locked state in the subduction appears with a certain stress concentration focusing on the microearthquake seismicity around the tokai district in central japan where a large interplate earthquake is feared to occur we tried to identify such an area of locked subduction on the philippine sea plate possibly related to the future earthquake we investigated the microearthquake seismicity from various perspectives first the hypocenter distribution was analyzed to identify the extent of the locked area the characteristic profile of the distribution was presumed to represent a stress concentrated area induced from the mechanical contact between both plates the second approach is to interpret stress patterns reflected in focal mechanisms the locked state was recognized and verified by a comparison of the p axis distribution pattern with that expected from a model imaging a partially locked subduction the third approach is to monitor the temporal change of the seismic wave spectrum analyzing predominant frequencies of p and s waves and monitoring their changes for a period of 10 years we found a trend of gradual increase common to both waves this means an increase of stress drop in microfracturings and in its turn implies accumulation of stress around the focus area the rate of the stress change converted from the frequency change was compared with the result derived from a numerical simulation the simulation performed on the basis of a constitutive friction law for a stick sliding on the plate interface computed a changing rate of the maximum shear stress around the locked zone and showed its spatial variation along the subduction axis thus the simulated result indicated a certain compatibility with the observed one although ambiguities and uncertainties still exist in the study all the results derived here seem to indicate an identical conclusion that the plate subduction is actually locked in this region at present

a bump on the upper surface of the philippine sea plate beneath the boso peninsula japan inferred from seismic reflection surveys a possible asperity of the 1703 genroku earthquake abstract to reveal a subsurface structure beneath the southern part of the boso peninsula japan where the philippine sea plate is subducting and great interplate earthquakes associated with the subduction occur repeatedly we conducted a new seismic reflection survey from march to april 2005 boso05 we also reanalyzed old multi channel seismic mcs survey data that had been collected off the boso peninsula in 1978 sk78 we found clear strong reflectors beneath the southern coast of the boso peninsula since common mid points cmps were distributed widely beneath the study area owing to the design of the receiver and shot lines of boso05 we selected appropriate directions of stacking lines to get the best image of the dipping reflectors by optimum azimuth search oas processing we carefully checked the seismic profiles at the intersections of the survey lines to confirm the nne dipping configuration of the strong reflectors these strong reflectors were interpreted as the upper surface of the subducting phs plate from their locations and the estimated velocities beneath the reflectors furthermore these reflectors revealed a topographic high bump beneath the southern coast of the boso peninsula where the source fault of the genroku earthquake of 1703 is thought to be located

tremor genic slow slip regions may be deeper and warmer and may slip slower than non tremor genic regions slow slip events sses are observed worldwide and often coincide with tectonic tremor notable examples of sses lacking observed tectonic tremor however occur beneath k lauea volcano hawaii the boso peninsula japan near san juan bautista on the san andreas fault california and recently in central ecuador these sses are similar to other worldwide sses in many ways e g size or duration but lack the concurrent tectonic tremor observed elsewhere instead they trigger swarms of regular earthquakes we investigate the physical conditions that may distinguish these non tremor genic sses from those associated with tectonic tremor including slip velocity pressure temperature fluids and fault asperities although we cannot eliminate the possibility that tectonic tremor may be obscured in highly attenuating regions slip velocities of sses at k lauea volcano 10 6 m s and boso peninsula 10 7 m s are among the fastest sses worldwide k lauea volcano the boso peninsula and central ecuador are also among the shallowest sses worldwide and thus have lower confining pressures and cooler temperatures in their respective slow slip zones fluids also likely contribute to tremor generation and no corresponding zone of high vp vs has been noted at k lauea or boso we suggest that the relatively faster slip velocities at k lauea volcano and the boso peninsula result from specific physical conditions that may also be responsible for triggering swarms of regular earthquakes adjacent to the slow slip while different conditions produce slower sse velocities elsewhere and trigger tectonic tremor

geometry and spatial variations of seismic reflection intensity of the upper surface of the philippine sea plate off the boso peninsula japan abstract in the region off the boso peninsula japan the pacific plate is subducting westward beneath both the honshu island arc and philippine sea plate while the philippine sea plate is subducting northwestward beneath the honshu island arc these complex tectonic interactions have caused numerous seismic events occurred in the past to better understand these seismic events it is important to determine the geometry of the plate boundary in particular the upper surface of the philippine sea plate we conducted an active source seismic refraction survey in july and august 2009 from which we obtained a 2 d p wave velocity structure model along a 216 km profile we used the velocity model and previously published data that indicate a p wave velocity of 5 0 km s for the upper surface of the subducting philippine sea plate to delineate its boundary with the overriding honshu island arc our isodepth contours of the upper surface of the philippine sea plate show that its dip is shallow at depths of 10 to 15 km far off the boso peninsula this shallow dip may be a result of interference from the pacific plate slab which is subducting westward under the philippine sea plate within our survey data we recognized numerous seismic reflections of variable intensity some of which came from the upper surface of the philippine sea plate an area of high seismic reflection intensity corresponds with the main slip area of the boso slow slip events our modeling indicates that those reflections can be explained by an inhomogeneous layer close to the upper surface of the philippine sea plate

discussion on development of polygonal fault systems a test of hypotheses d m d james writes the mechanics of formation of polygonal faults are widely acknowledged as not yet fully understood and it is welcome that goulty swarbrick 2005 attempt a discriminatory test between rival hypotheses it is however important that such a test bears some relation to physical reality the test is based on the assumption that the ratio of horizontal to vertical effective stress as deduced from leak off tests in two wells in the north sea at depths of about 2 km yields the co efficient of earth pressure at rest therein and hence the residual friction governing the post nucleation development of polygonal faults apparently globally and at any depth it is not clear if the authors consider that the polygonal fault tiers at the well sites are currently active neither is it clear if they assume that the coefficient of residual friction along the fracture is a reasonable approximation to the coefficient of initial friction which governs the dip of the propagating fracture tip and the fault surface as a whole relative to the orientation of the vertical effective stress it is hardly surprising that the ratio of horizontal to vertical effective stress k is very high in the wells analysed the leak off tests are from highly overpressured horizons ratios of pore fluid pressure to total vertical stress approximately 0 80 and 0 84 and the effect of pore fluid pressure coupling hillis 2003 will inevitably decrease the value of the horizontal effective stress to lesser extent than it does the vertical effective stress it is certainly not yet demonstrated that polygonal faults require overpressures of this magnitude for their formation by any mechanism leak off tests tend to overestimate the horizontal effective stress if no correction is made for the excess mud pressure necessary to overcome the tensile strength of

stress fields in and around metropolitan osaka japan deduced from microearthquake focal mechanisms abstract present day stress fields in and around metropolitan osaka japan have been investigated based on 238 microearthquake focal mechanism solutions from approximately the past 10 years the successful retrieval of the focal mechanisms in the noisy urban area owed much to the clean seismic data recorded at four borehole observatories deeper than 500 m depth in osaka prefecture in which p wave onset polarity of the microearthquake could be clearly identified we found many microearthquakes with a pure reverse faulting mechanism which is consistent with the faulting style of major active faults within the area 42 km long east dipping uemachi and 38 km long east dipping ikoma fault zones however a considerable number of microearthquakes with strike slip components were also found to occur most of the p axes are oriented in the ese wnw to ene wsw directions sub horizontally conforming to the general tectonic trend of the area the analysis of a stress tensor inversion delineated small but noticeable differences in stress regime on a scale of at least 10 km where strike slip faulting prevails throughout the region but the middle and southern sections of the uemachi fault zone contain some reverse faulting components based on the estimated stress fields together with assumptions regarding the deep geometry of the uemachi fault zone we assessed the reactivation potential of the fault zone through slip tendency analysis the results indicate higher potential in the middle and southern sections of the fault zone which is related to the locally increased reverse component detected there

tidal triggering of earthquakes in the subducting philippine sea plate beneath the locked zone of the plate interface in the tokai region japan we found a characteristic space time pattern of the tidal triggering effect on earthquake occurrence in the subducting philippine sea plate beneath the locked zone of the plate interface in the tokai region central japan where a large interplate earthquake may be impending we measured the correlation between the earth tide and earthquake occurrence using microearthquakes that took place in the philippine sea plate for about two decades for each event we assigned the tidal phase angle at the origin time by theoretically calculating the tidal shear stress on the fault plane based on the distribution of the tidal phase angles we statistically tested whether they concentrate near some particular angle or not by using schuster s test in this test the result is evaluated by pvalue which represents the significance level to reject the null hypothesis that earthquakes occur randomly irrespective of the tidal phase angle as a result of analysis no correlation was found for the data set including all the earthquakes however we found a systematic pattern in the temporal variation of the tidal effect the p value significantly decreased preceding the occurrence of mz4 5 earthquakes and it recovered a high level afterwards we note that those mz4 5 earthquakes were considerably larger than the normal background seismicity in the study area the frequency distribution of tidal phase angles in the pre event period exhibited a peak at the phase angle where the tidal shear stress is at its maximum to accelerate the fault slip this indicates that the observed small p value is a physical consequence of the tidal effect we also found a distinctive feature in the spatial distribution of p values the small p values appeared just beneath the strongly coupled portion of the plate interface as inferred from the seismicity rate change in the past few years d 2005 elsevier b v all rights reserved

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

joint focal mechanism determination with source region station corrections using short period body wave amplitude data abstract we have developed a method that simultaneously determines focal mechanism solutions of many small earthquakes and source region station corrections for short period body wave amplitudes by inverting amplitude data of p sh and sv waves together with p wave polarity data the observed seismic waveform includes the effects of site amplification and attenuation along its ray path in addition to the radiation pattern of earthquake source the amplitude of seismograms at frequencies higher than a few hertz is extremely sensitive to heterogeneous structure near the ground surface consequently we need to know in detail the effects of site amplification and attenuation in order to estimate focal mechanisms by using short period waveforms however at present we do not know the detailed crustal structure with a resolution necessary for this estimation in the present study we assume that p and s wave attenuation factors along ray paths from hypocenters to each station can be expressed as a function of hypocentral distance backazimuth and incident angle based on this assumption we determined focal mechanism solutions of many earthquakes and the coefficients in the function for each station simultaneously by using p sh and sv wave amplitudes and p wave polarities we applied the present method to 170 aftershocks of the 1996 onikobe earthquake m 5 9 which occurred in the central part of northeastern japan we obtained focal mechanism solutions of many microearthquakes whose mechanism solutions could not be determined by using p wave polarity data alone p axes of almost all the obtained focal mechanism solutions are horizontal and oriented in the east west direction t axes are on average near vertical at the shallowest depth as the depth approaches 5 km the t axes become horizontal and then gradually become near vertical again

repeating earthquake activities associated with the philippine sea plate subduction in the kanto district central japan a new plate configuration revealed by interplate aseismic slips abstract we detect repeating earthquakes associated with the philippine sea plate subduction to reveal the plate configuration in the kanto district we find 140 repeating earthquake groups with 428 events by waveform similarity analysis most repeating earthquakes in the eastern part of the kanto district occur with a regular time interval they have thrust type focal mechanisms and are distributed near the upper surface of the philippine sea plate these observations indicate that the repeating earthquakes there occur as a repetition of ruptures on the isolated patches distributed on the plate boundary owing to the concentration of stress caused by aseismic slips in the surrounding areas this shows that the distributions of repeating earthquakes suggest the aseismic slips in the surrounding areas of small patches we determine spatial distributions of repeating earthquakes in the eastern part of the kanto district and find that they correspond to the upper boundary of the philippine sea plate that is the upper boundary of the oceanic crust layer of the philippine sea plate the plate geometry around choshi is newly constrained by repeating earthquake data and a rather flat geometry in the eastern part of the kanto district is revealed the obtained geometry suggests uplift of the philippine sea plate due to the collision with the pacific plate beneath choshi repeating earthquakes in the western part of the kanto district have extremely shorter recurrence times and their focal mechanisms are not of the thrust types these repeating earthquakes are classified as burst type activity and likely to occur on the preexistent fault planes which are distributed around the collision zone between the philippine sea plate and the inland plate the variation among the repeating earthquake activities in the kanto district indicates that regular repetition of repeating earthquakes is possible only on the plate boundary with a smooth and simple geometry

p wave anisotropic tomography of the nankai subduction zone in southwest japan 1 the active subduction of the young philippine sea phs plate and the old pacific plate has resulted in significant seismic heterogeneity and anisotropy in southwest sw japan in this work we determined a detailed 3 d p wave anisotropic tomography of the crust and upper mantle beneath sw japan using 540 000 p wave arrival times from 5 249 local earthquakes recorded by 1095 stations the phs slab is imaged clearly as a high velocity high v anomaly which exhibits considerable lateral variations significant low velocity low v anomalies are revealed above and below the phs slab the low v anomalies above the phs slab may reflect the upwelling flow in the mantle wedge and the phs slab dehydration and they form the source zone of the arc volcanoes in sw japan the low v zones under the phs slab may reflect the upwelling flow in the big mantle wedge above the pacific slab the anisotropy in the crust and upper mantle is complex in kyushu the p wave fast velocity direction fvd is generally trench normal in the mantle wedge under the back arc which is consistent with the corner flow driven by the phs slab subduction the fvd is trench parallel in the subducting phs slab under kyushu we think that the intraslab seismicity is a potential indicator to the slab anisotropy that is the phs slab with seismicity has kept its original fossil anisotropy formed at the mid ocean ridge while the aseismic phs slab has reproduced the anisotropy according to its current deformation

revised models for hydrocarbon generation migration and accumulation in jurassic coal measures of the turpan basin nw china abstract whether or not the lower middle jurassic coal measures in the turpan basin of nw china have generated commercial quantities of liquid petroleums is a problem of considerable importance that remains contentious as it has not yet been resolved unequivocally this study provides evidence against the jurassic humic coals as the only major source for the oils discovered in the taibei depression of this basin and suggests additional significant contributions from the upper permian and middle lower jurassic lacustrine source rocks the carboniferous permian marine source rocks may have been important also in limited locations along the major basement faults molecular and petrographic data indicate that the majority of the middle jurassic strata are currently immature or marginally mature with respect to hydrocarbon generation within the major depocenters the middle lower jurassic coal bearing strata of the baodaowan and xishanyao formations has reached the conventional oil window i e with vitrinite reflectance 0 7 ro pre jurassic upper permian in particular derived hydrocarbons appear to be widespread in extracts of fractured jurassic coal and fine grained rocks large differences have been observed in the absolute concentrations of biomarker compounds in rock extracts of various source intervals thus coaly biomarker signatures of the oils most likely resulted from mixing and migration contamination when hydrocarbons derived from mature source rocks migrated up through highly fractured coal seams along deep seated faults in addition to conventional exploration targets revised petroleum generation and accumulation models predict that the focus in the turpan basin should also include deep structures within the carboniferous permian strata and subtle low magnitude anticlines and stratigraphic traps within the triassic jurassic sections crown copyright

strain partitioning in the zone of transition from nankai subduction to izu bonin collision central japan implications for an extensional tear within the subducting slab abstract the izu bonin ridge collision with central japan is a type example of collision of two island arcs in a subduction context based on the analysis of active faults paleomagnetic data and recent seismicity in the northern tip of the izu bonin arc and the adjacent oceanic plate we propose a tectonic schema of the izu collision system and its transition to the nankai subduction to the west the dense gps network deployed in central japan allows us to constrain the kinematics of the different blocks identified this new kinematic model demonstrates the essential role of strain partitioning there as the northward component of the izu bonin arc motion is locked in the collision zone 30 of the convergence between the philippine sea plate and central japan is accommodated within the philippine sea slab along the zenisu east izu deformation system we show that this pattern of deformation is related to an extensional tear of the philippine sea slab propagating southward along the volcanic arc we discuss the implications of this kinematic model on the seismogenic potential of the area and the dynamics of the central japan convergence zone

molecular and isotopic evidence for mixed source oils in subtle petroleum traps of the dongying south slope bohai bay basin abstract subtle traps have become an important petroleum play type for exploration in the dongying depression bohai bay basin eastern china the majority of the oil pools are in the middle interval of the es3 member e s 3 m of the eocene oligocene shahejie formation with the subtle traps being primarily in the lenticular basin floor turbidite sands enclosed within basin floor mudstones detailed geochemical investigation of 68 oil and rock samples from the depression reveals that in contrast to previous models the oils from the subtle traps correlate poorly with the surrounding e s 3 m source rocks while the high pristane phytane pr ph 1 and low gammacerane c30 hopane ratios in these source rocks represent a freshwater lacustrine setting the oils feature low pr ph ratios e s 4 u source rocks deposited in a brackish lacustrine setting the compound specific isotope ratios of n alkanes in the oils have intermediate values between those observed in extracts from the lower es3 e s 3 l and upper es4 e s 4 u source rocks consequently the oils in the e s 3 m subtle traps were most likely derived from mixed e s 3 l and e s 4 u sources with the contribution from the e s 4 u source rocks being predominant the oils generated from the e s 4 u source rocks must have migrated through a thick interval of the e s 3 l source rocks to reach the subtle traps in the e s 3 m through which there are no apparent structural nor stratigraphic pathways the traditional migration and accumulation model i e indigenous crude oil with short migration distance to lenticular oil pools should be revised to account for the charging of oils from e s 4 u source rocks

the development of polygonal fault systems by syneresis of colloidal sediments abstract polygonal fault systems occur in numerous sedimentary basins worldwide are generally located on passive margins in onlap fill units and tend to comprise the finest grained sediments in this geological setting these fault systems have been most thoroughly described in the central north sea basin and the detailed structure shows a significant correlation with lithological variations both vertically and laterally extension measured in stacked decoupled tiers of polygonal faults correlates positively with both clay fraction and smectite content lateral facies variations are also observed and indicate that time equivalent sequences upslope from the smectite rich polygonally faulted sediments are coarse grained clay poor and undeformed this leads us to believe that the structure and geometry of the fault system are controlled by the colloidal nature of the sediments and that the volumetric contraction measured on seismic sections can be accounted for by syneresis of colloidal smectitic gels during early compaction syneresis results from the spontaneous contraction of a sedimentary gel without evaporation of the constituent pore fluid this process occurs due to the domination of interparticle attractive forces in marine clays dependent on environment and is governed by the change of gel permeability and viscosity with progressive compaction the process of syneresis can account for a number of structural features observed within the fault systems such as tiers of faults the location of maximum fault throw and growth components at upper fault tips as such this paper represents the first attempt to correlate microscale properties of clay rich sediments to their macroscale seismic character

guidelines for assessing the petroleum potential of coaly source rocks using rock eval pyrolysis abstract coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using rock eval pyrolysis the rank threshold for oil generation is indicated by the increase in bi s1 toc at rank sr 9 10 tmax 420 430 c ro 0 55 0 6 and the threshold for oil expulsion is indicated by the peak in qi s1 s2 toc at rank sr 11 12 5 tmax 430 440 c ro 0 65 0 85 the pronounced rank related increase in hi s2 toc prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation a more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion alternatively effective hi values i e his near the onset of expulsion can be estimated by translating the measured his of immature samples along the maturation pathway defined by the new zealand or other defined coal band coaly source rocks comprise a continuum of coaly lithologies including coals shaly coals and coaly mudstones determination of the total genetic potential of coaly source rock sequences is best made using lithology based samples near the onset of expulsion

subduction influence of philippine sea plate on the mantle beneath northern kyushu sw japan an examination of boron contents in basaltic rocks abstract northern kyushu characterized by the subduction of two oceanic slabs a hot shikoku basin and a cold philippine sea plate beneath the eurasian plate forms a complex portion of southwestern japan arc in order to evaluate the effect of slab derived fluids from these two contrasting oceanic plates we determined the boron b contents in basaltic rocks from ten volcanoes and three old volcanic fields which erupted since 11 ma since b is distinctly concentrated into slab derived fluids among the earth s materials we attempted to estimate the influences of subduction on the sub arc mantle composition from the interpretation of the b data in basaltic rocks old 11 6 ma basaltic rocks contain low ratios of b sm 0 5 1 3 b zr 0 02 0 05 and b nb 0 2 0 5 suggesting little influence of subduction similarly backarc basaltic rocks occurring throughout the observed period show little influence of subduction in contrast volcanic products from young aso volcano located at the volcanic front show a strong influence of subduction as indicated by the high b sm 1 6 4 3 b zr 0 07 0 16 and b nb 1 4 3 7 ratios after 6 ma the volcanic arc segment containing aso volcano is associated with the subduction of the cold philippine sea plate hence a b rich fluid was probably added to the sub arc mantle however yufu tsurumi and kuju volcanoes which are located at the same volcanic front show small b sm 0 9 1 9 b zr 0 04 0 07 and b nb 0 5 0 9 ratios this implies that the subduction of the hot shikoku basin released fluids from the slab at shallow depths therefore it is depleted of b and other subduction components by the time it reaches the volcanic front

development of polygonal fault systems a test of hypotheses polygonal networks of normal faults in layer bound sequences of fine grained mudstones have formed without regional tectonic extension the two leading hypotheses concerning the generic mechanism responsible for their development are 1 horizontal stresses are reduced by syneresis 2 coefficients of residual friction are very low to discriminate between these hypotheses the ratios between the minimum horizontal and the vertical effective stresses have been estimated in four north sea wells penetrating oligocene and miocene sequences that contain polygonal fault networks the effective stress ratios are c 0 8 consistent with very low coefficients of friction but not with syneresis

combining palynofacies and petrography in the study of sub bituminous tropical coals a case history from lower tertiary coals in colombia abstract colombia contains large coal reserves of late cretaceous to cenozoic age in various sedimentary basins but little is known about their potential to generate hydrocarbons in western venezuela coals are known to be potential source rocks for oil and the vicinity of these coals with coal bearing basins in colombia has prompted new studies in colombian tropical coals to develop concepts about their hydrocarbon generating potential the paleogene amaga formation studied here although of limited geographical extension is an ideal field laboratory which contains low rank coal seams in which the transformation and preservation state of organic matter permits the assessment of environment and vegetation types existing at the time of peat formation several seams up to 1 m thick have been analyzed using both bulk seam samples and ply or lithotype samples it is demonstrated that bulk seam samples are not representative for a proper evaluation of the hydrocarbon generation potential of seams one needs to evaluate all lithotype assemblages within a seam proximate analysis and rock eval pyrolysis provide a rapid and cheap way to assess the generation potential of each lithotype the potentially interesting lithotypes can be further analyzed through the combination of petrographic and palynological observations these methods permit the comparison of coal macerals with the equivalent palynofacies constituents provided that a preparation technique especially designed for tropical sub bituminous tertiary coals is used the palynofacies technique has proved to be more accurate than petrography in determining the relative proportion of the potentially oil prone constituents macerals which can be hidden or difficult to identify in petrographic polished section moreover the comparison between resinite oil observed in petrography and resins identified in palynofacies may yield indications of early hydrocarbon generation this methodology provides a fully detailed inventory of coal properties with respect to hydrocarbon generation potential the use of palynofacies is an additional tool to apprehend the floral composition and paleoenvironment of coals thereby increasing the geological and geochemical database needed to evaluate their potential such a methodology may prove very important to assess the petroleum potential of thicker coal deposits in prospective petroleum provinces such as the cerrejon coals in northern colombia

geochemical and petrological evidence for tertiary terrestrial and cretaceous marine potential petroleum source rocks in the western kamchatka coastal margin russia abstract rock eval pyrolysis and microscopic analyses of palaeogene terrestrial strata from the western kamchatka coastal margin russia indicate that good oil prone source rocks are present in both coals and shales hydrogen indices hi of up to 493 mg hc g toc are present in low maturity 0 45 r o vitrinite shale samples from the irgirninvayam river delta region whereas coals with 0 37 0 75 r o and hi of 270 310 mg hc g toc comprise potential oil gas and oil prone source rocks in the kvachincha bay tigel coastal and rassoshina napanskaya river areas the shales and coals with the highest petroleum potential were deposited in a freshwater paleo setting and consist of gelovitrinite cutinite suberinite sporinite resinite and matrix bituminite molecular geochemistry was also used to group genetically related oil samples and to postulate the likely petroleum systems in this area while the preliminary data confirm the origin of two families of oils from the palaeogene deltaic to marginal lacustrine source rocks the chemical composition of oils in two other families suggests the possible presence of marine source rocks in not yet penetrated upper cretaceous paleocene sequences of the basin

source rock quality determination from oil biomarkers ii a case study using tertiary reservoired beaufort sea oils biomarkers molecular fossils in 26 beaufort sea mackenzie delta oils reveal three genetic oil groups and suggest descriptions of their probable sources group 1 21 tertiary reservoired oils was soured from tertiary deltaic sediments group 2 three cretaceous and one devonian reservoired oil and group 3 one lower cretaceous reservoired oil derive from two high quality sources deposited in open marine environments geographical variations in the geochemistry of the 21 group 1 oils suggest that their deltaic source was substantially more oil prone in the distal deltaic portions than in the region closer to the paleoshoreline although these data do not address source rock volumes they do indicate that poor source quality is not a cause of underfilled traps in the o fshore the map pable lateral variations in group 1 oil compositions illustrate how in basins with vertically drained sources lateral source rock facies changes can bc inferred from regional variations in the geochemistry of the overlying oils furthermore the data suggest that geochemical studies attempting to deduce genetic relationships between geographically separated oils should carefully consider the potential effects of source rock facies changes on the oil compositions

three dimensional fine velocity structure and hypocentral distribution of earthquakes beneath the kanto tokai district japan we determine the three dimensional p wave velocity structure beneath the kanto tokai district central japan and simultaneously relocated by inverting travel time data for 91 events that were observed at 61 stations operated by the national research center for disaster prevention the variance of the travel time data is reduced by 75 as compared to the variance for the routinely used laterally homogeneous model in general our velocity model is consistent with tectonic models of the kanto tokai district our velocity model is also in good agreement with seismic explosion data and bouguer gravity anomalies the uppermost layer from 0 to 16 km depth is characterized by lateral velocity differences of more than 20 we find low velocity zones beneath tokyo bay the middle of the boso peninsula and omae zaki where there are thick sedimentary layers a marked 30 km thick high velocity zone extends to the northeast and the west of the izu peninsula this zone dips gradually from the surface to a depth of 70 km in the eastern region and to a depth of 40 km in the western region and is interpreted as the philippine sea phs plate which is being subducted at the sagami and the suruga troughs the data unquestionably require a high velocity zone beneath mount tsukuba that cannot be explained in terms of present tectonic models we use our three dimensional velocity model to relocate about 23 000 earthquakes that took place from 1983 through 1985 the accuracy of the hypocentral parameters improved considerably as a result the double seismic zone within the subducting pacific plate is more clearly delineated than in previous studies the inclined seismic zone for the subducting phs plate coincides fairly well with the high velocity zone of our three dimensional velocity model

thickness variation of the descending philippine sea slab and its relationship to volcanism beneath the kanto tokai district central japan 1 we use an iterative nonlinear travel time tomography technique to determine three dimensional p wave and s wave seismic velocity models for the region beneath the kanto tokai district of central japan salient points of the models are the following 1 the subducting philippine sea slab has thickness variation with a stepwise offset east of the izu peninsula the eastern beneath the kanto district and western beneath the area north of izu peninsula and the tokai district regions have respective thicknesses of 60 and 25 km the slab clearly subducts continuously to a depth of 100 km from the sagami trough beneath the kanto district although the tokai slab is indistinct at depths of 50 70 km 2 the oceanic crust at the top of the descending philippine sea slab transforms into eclogite at a depth of about 70 km beneath the kanto district 3 low velocity anomalies are associated with present and past volcanism they are located on the west of a 110 km depth contour of the wadati benioff zone rather than only on the backarc side of the volcanic front deflection of the volcanic front might result from the subducting philippine sea slab which shifts the dehydration reaction deeper as it subducts deeper

geofem kinematic earthquake cycle simulation in southwest japan we construct a viscoelastic fem model with 3 d configuration of the subducting philippine sea plate in southwest japan to simulate recent 300 year kinematic earthquake cycles along the nankai suruga sagami trough based on the kinematic earthquake cycle model this 300 year simulation contains a series of three great interplate earthquakes the inclusion of viscoelasticity produces characteristic velocity field during earthquake cycles regardless of the assumed constant plate coupling throughout the interseismic period just after the occurrence of interplate earthquakes the viscoelastic relaxation creates the seaward motion in the inland region in the middle period the seaward motion gradually decreases and the resultant velocity field is similar to the elastic one later just before the next interplate earthquake displacements due to the interplate coupling in the viscoelastic material are distributed more broadly in the forearc region than in the purely elastic one since the viscoelastic relaxation due to the previous earthquake mostly disappears the effects of such interplate earthquake cycles on five major inland faults in southwest japan where large intraplate earthquakes occurred during this period are quantitatively evaluated using the coulomb failure function cff the calculated change in cff successfully predicts the occurrence of the 1995 kobe earthquake m 7 the occurrence of other inland earthquakes however cannot be explained by the calculated changes in cff and especially the 1891 nobi earthquake m 8 the largest inland earthquake in japan which occurred at the time close to the local minimum of cff this implies that further improvements are necessary for our fem modeling such as the modeling of steady east west compressive force and stress interactions between the inland faults

low velocity oceanic crust at the top of the philippine sea and pacific plates beneath the kanto region central japan imaged by seismic tomography 1 we construct fine scale three dimensional p and s wave velocity structures beneath the kanto region central japan by seismic tomography with a spatial correlation of velocities the philippine sea and pacific plates subduct beneath the eurasian plate in this area and are imaged with high velocities oceanic crust at the uppermost part of these subducting plates is a low velocity layer low velocity oceanic crust of the philippine sea plate subducts to a depth of approximately 80 km there are also two low velocity bodies with relatively high v p v s ratios of 1 80 1 90 in the mantle wedge above the oceanic crust of the philippine sea plate we speculate that the westernmost of these two low velocity bodies consists of 20 partially serpentinized peridotite continuous with gabbro in the oceanic crust of the uppermost philippine sea plate while the eastern body is composed of 30 partially serpentinized peridotite we trace the subducting oceanic crust of the pacific plate to a depth of 120 km the estimated v p v s ratio of this layer is 1 85 1 90 which indicates a low probability of molten rock the gabbroic oceanic crust may have been metamorphosed to garnet granulite

configuration of subducting philippine sea plate and crustal structure in the central japan region a seismic experiment with six explosive sources and 391 seismic stations was conducted in august 2001 in the central japan region the crustal velocity structure for the central part of japan and configuration of the subducting philippine sea plate were revealed a large lateral variation of the thickness of the sedimentary layer was observed and the p wave velocity values below the sedimentary layer obtained were 5 3 5 8 km s p wave velocity values for the lower part of upper crust and lower crust were estimated to be 6 0 6 4 and 6 6 6 8 km s respectively the reflected wave from the upper boundary of the subducting philippine sea plate was observed on the record sections of several shots the configuration of the subducting philippine sea slab was revealed for depths of 20 35 km the dip angle of the philippine sea plate was estimated to be 268 for a depth range of about 20 26 km below this depth the upper boundary of the subducting philippine sea plate is distorted over a depth range of 26 33 km a large variation of the reflected wave amplitude with depth along the subducting plate was observed at a depth of about 20 26 km the amplitude of the reflected wave is not large and is explained by the reflected wave at the upper boundary of the subducting oceanic crust however the reflected wave from reflection points deeper than 26 km showed a large amplitude that cannot be explained by several reliable velocity models some unique seismic structures have to be considered to explain the observed data such unique structures will provide important information to know the mechanism of inter plate earthquakes d 2004 elsevier b v all rights reserved

double saloon door tectonics in the japan sea fossa magna and the japanese island arc abstract a number of criteria considered diagnostic of double saloon door rifting and seafloor spreading are matched by data from the japanese arc these include i a pair of terranes sw and ne honshu which rotated in opposite directions from 22 21 ma to 14 11 ma ii rotated terranes which comprise a retro arc fold thrust belt attached to an accretionary wedge intruded by a magmatic arc iii contemporaneous backarc extension from 24 to 21 ma which is brought to a halt by progressive collision of the izu bonin and japan arcs from 15 to 5 ma iv isolation of blocks of thicker continental crust by areas of thin continental or oceanic crust during backarc rifting v such isolation may be due to simultaneous rifting or to progressively seaward rifts associated with ridge jumps towards the subduction zone vi opposite rotations are accommodated by subduction rollback demonstrated by seaward migration of the volcanic front from 30 26 ma to 16 15 ma vii concurrent development of a major arc orthogonal rift the fossa magna from 23 18 ma to 14 ma which was thereafter inverted from 15 ma to the recent viii a northeast propagating rift in the northern japan basin demonstrated by the relationship of linear magnetic anomalies to the mapped continent ocean boundary driving mechanisms for double saloon door tectonics are discussed in relation to various reconstructions of the northwest pacific opposite rotational torques leading to opposite terrane rotations may be caused by rollback of a curved trench hingeline or by the divergent slab sinking forces of the pacific and philippine sea plates

seismic wavefield imaging of long period ground motion in the tokyo metropolitan area japan long period ground motions due to large earthquakes can cause devastating disasters especially in urbanized areas located on sedimentary basins to assess and mitigate such damage it is essential to rapidly evaluate seismic hazards for infrastructures which can be simulated by seismic response analyses that use waveforms at the base of each infrastructure as an input ground motion the present study reconstructs the seismic wavefield in the tokyo metropolitan area located on the kanto sedimentary basin japan from seismograms of the metropolitan seismic observation network meso net the obtained wavefield fully explains the observed waveforms in the frequency band of 0 10 0 20 hz this is attributed to the seismic wavefield imaging technique proposed by kano et al 2017 which implements the replica exchange monte carlo method to simultaneously estimate model parameters related to the subsurface structure and source information further investigation shows that the reconstructed seismic wavefield lower than 0 30 hz is of high quality in terms of variance reduction which quantifies a misfit in waveforms but that the variance reduction rapidly worsens in higher frequencies meanwhile the velocity response spectra show good agreement with observations up to 0 90 hz in terms of the combined goodness of fit which is a measure of misfit in the velocity response spectra inputting the reconstructed wavefield into seismic response analyses we can rapidly assess the overall damage to infrastructures immediately after a large earthquake

the origin of large or great thrust type earthquakes along subducting plate boundaries abstract seismicity deformation state of stress and abundance of fluids along subducting plate boundaries are reviewed and the origin of large or great thrust type earthquakes is discussed based on the recent experimental results on the slip behavior of halite and serpentine gouges shallow subducting plate boundaries above 20 25 km in depth are characterized by low seismicity low tectonic stress inter plate decoupling ductile deformation associated with the formation of metamorphic schistosity except at very shallow depths metamorphism suggesting solution processes on massive scale and presence of abundant h 2 o it is argued that these unique features are due to pressure solution processes to high fluid pressure to low strength and stable behavior of clayey sediments under wet environments and or to the deformation of soft unconsolidated sediments at very shallow depths the low seismicity in this zone is in marked contrast with major strike slip faults along which large earthquakes occur at depths shallower than 15 20 km it is emphasized that these unique features are expected only for restricted regions where there is constant supply of h 2 o due to progressive metamorphism or where fluids in the rocks are trapped and cannot escape to the surface large or great thrust type earthquakes in subduction zones initiate at depths of 30 50 km below the shallow decoupled zone in this focal depth range the supply of h 2 o during progressive metamorphism perhaps diminishes downwards the overriding and subducting plates are coupled and stick to each other during much of the inter seismic period and the resistance to slip or shear stress is presumably high it is suggested that these earthquakes begin to occur at a depth where the plate boundary zone becomes fairly dry deformation at these depths appears to be predominantly ductile so that the earthquakes cannot be regarded simply as a brittle phenomenon 1 creep instability i e instability associated with plastic deformation and 2 dehydration induced instability are the most likely mechanisms for initiating the earthquakes and both have some experimental support stick slip of halite gouge while undergoing ductile deformation primarily by intracrystalline gliding is described and discussed as a supporting evidence for 1 shear resistance of halite gouge increases with increasing confining pressure in stick slip regimes hence the observed stick slip may be a semi brittle phenomenon with respect to the pressure dependence of the shear resistance although the deformation texture cannot be distinguished from that formed by pressure insensitive flow serpentine gouge exhibits violent stick slip upon its decomposition under dry not wet environments supporting the mechanism 2 above exact mechanisms which lead to the unstable fault motion are poorly understood as yet but stick slip of both halite and serpentine gouges is recognized only when the slip rate dependence of friction is negative i e lower friction at faster slip rate consistent with the theoretical prediction of rice and ruina 1983 there is a possibility that the thrust type earthquakes can be explained essentially within the framework of fault constitutive laws developed by dieterich 1979 and ruina 1983

a new configuration and an aseismic slab of the descending philippine sea plate revealed by seismic tomography abstract we obtained the three dimensional seismic velocity structure of the uppermost mantle beneath the kanto tokai and chubu regions central japan where the philippine sea plate descends by means of travel time tomography using 18 years of p phase data recorded by a regional seismic network a distinct low velocity zone which was the oceanic crust of the descending philippine sea plate was found beneath the kanto region the low velocity zone revealed a new configuration of the philippine sea plate different from any models obtained through the analysis of hypocenter distribution and focal mechanisms we also found a high velocity area in the deep aseismic region below the volcanic front between the kanto and chubu regions it extends to the philippine sea plate in both regions it was likely to be an aseismic extended section of the philippine sea plate the existence of the aseismic philippine sea plate beneath the chubu region was confirmed there was another low velocity area beneath the active volcanoes high poisson s ratio areas were found both beneath the volcanoes and in the low velocity zone of the philippine sea plate near the volcanic front under the kanto region

polygonal cracks in bedrock on earth and mars implications for weathering polygonal crack systems with domal microrelief imaged by the mars exploration rover mer opportunity show remarkable similarity to terrestrial crack systems developed on outcrop surfaces study of jurassic navajo sandstone surfaces show development of crack systems in relatively isotropic host rock as a result of tensile weathering stresses these terrestrial analogs are utilized to understand potential weathering processes on mars

crustal heterogeneity as inferred from seismic coda wave decomposition by small aperture array observation abstract seismic coda waves have complex waveforms and are considered to be caused by 3 dimensional structural heterogeneities we carried out 3 component small aperture array observations of seismic coda waves from natural earthquakes in tsukuba central japan to decompose complex coda waveforms and to clarify the nature of crustal heterogeneity epicentral distances in the present study are less than 200 km the observational results are summarized as follows 1 the remarkable feature of the coda from natural earthquakes is the difference between the p coda and the s coda especially in the vertical component the p coda consists mainly of coherent p wave phases which have almost the same slowness vector as the initial p wave motion whereas the s coda is decomposed into incoherent phases with random propagation directions 2 coherency of waveforms among the array sensors of the vertical component rapidly becomes low from the high value of coherency of the direct s wave 3 in the two horizontal components radial and transverse ones both the p and s coda are decomposed into incoherent random phases 4 coherency in the early s coda of the horizontal components gradually becomes low compared to the vertical component these features indicate that s to p converted waves at horizontal boundaries of the structure are dominant in the p coda of the vertical component while the p coda of the horizontal components and the s coda consist of scattered waves from the lateral heterogeneity this interpretation leads to a model of crustal heterogeneity in which the degree of the lateral heterogeneity is smaller than the degree of vertical heterogeneity of layered structures

organic geochemistry and organic petrology of a potential source rock of early eocene age in the beaufort mackenzie basin abstract the biological marker compounds 17 h and 17 h 23 28 bisnorlupane have been identified in a coaly interval at about 3300 3320 m depth within the lower taglu sequence early eocene in the immiugak a 06 well in the beaufort mackenzie basin these biomarkers were previously only known to occur in the lower part of the richards formation and were thus used to infer that the richards was the source for most of the tertiary oils and condensates in the basin the discovery of bisnorlupanes in older much more organic rich rocks indicates that the previous oil source rock correlations may not have been correct and that the coals in the lower taglu sequence are likely the dominant effective source rock especially for the paleocene and early eocene reservoirs in the southern part of the mackenzie delta petrographic and rock eval analyses indicate that the lower taglu sequence coaly section should be mainly a source for gas but with some potential to expel liquids the level of thermal maturity inferred from rock eval tmax 432 438 c equivalent to about 0 65 0 75 ro vitrinite is slightly higher than that inferred from the measured reflectance fluorescence and foraminiferal colouration index which all indicate that the maturity at 3300 m is about 0 60 0 65 ro vitrinite equivalent at the gulf et al immiugak a 06 well site

imaging of the early acceleration phase of the 2013 2014 boso slow slip event we analyze gps and seismic data to examine the spatiotemporal evolution of a slow slip event sse near boso peninsula central japan from december 2013 to january 2014 the evolution of this sse and its associated seismicity is divided into two distinct phases slip initially accelerated slowly with low slip rates low propagation speeds and no accompanying seismicity during the early phase and then accelerated more rapidly with higher slip rates a higher propagation speed and local earthquake swarm activity during the later phase the seismicity was highly correlated in space and time with slip rate suggesting that the swarm activity was triggered by stress loading due to the slow slip the transition from the slow to faster phase shares some similarities with the nucleation of megathrust earthquakes inferred from foreshock activities suggesting that sses may provide insights into the nucleation of large earthquakes

guidelines for evaluating petroleum source rock using programmed pyrolysis rock eval pyrolysis is used to rapidly evaluate the petroleum generative potential and thermal maturity of rocks accurate conclusions require programs every 30 60 ft 9 18 m understanding of interpretive pitfalls and supporting data such as visual kerogen vitrinite reflectance and elemental analyses the generative potential of coals is commonly overestimated by pyrolysis and is best determined by elemental analysis and organic petrography most coals show high s2 s3 5 and low hi values 300 mg hc g toc migrated oil and mud additives which alter rock eval data can sometimes be removed by special processing for immature rocks bimodal s2 peaks and pi values over 0 2 indicate contamination pyrolysis downgrades organic poor clay rich rocks which show lower hi and higher tmax values than isolated kerogen because of adsorption of pyrolyzate on the clays tmax values for small s2 peaks 0 2 mg hc g toc are unreliable tmax is affected by maturation organic matter type contamination and the mineral matrix s3 is sensitive to inorganic and adsorbed carbon dioxide and to instrumentation problems acidification of carbonate rich samples and proper maintenance improves s3 measurement constant sample weights 100 mg are recommended below a threshold weight tmax increases by up to 10 c and other parameters decrease organic rich samples which overload the detector can be diluted with carbonate detector linearity is determined by pyrolyzing various weights of an organic rich rock

source rock quality determination from oil biomarkers i a new geochemical technique biomarker analyses of the aspen shale mowry shale equivalent skully s gap wyoming suggest that vital source rock properties e g kerogen hydrogen to carbon h c ratio rock eval hydrogen index hi and maceral composition may be indirectly yet quantitatively predicted from the biomarker parameters measured in oils a strong correlation exists between the homohopane index of aspen source rock extracts and both the h c ratio and hi of the associated kerogen r2 0 93 and 0 83 respectively the percentages of c30 and c28 4 desmethyl steranes relative to total extracted 4 desmethyl steranes correlate with the percentage of marine derived amorphous type ii organic matter in the kerogen r2 0 80 and 0 73 respecti ely and with kerogen h c ratio and hi r2 0 89 and 0 88 respectively for c30 steranes r2 0 89 and 0 83 respectively for c28 steranes the ratio of 4 agr methyl 24 ethylcholestanes to 3s methyl 24 ethylcholestanes in the extracts also correlates with kerogen h c ratio and hi r2 0 93 and 0 92 respectively in contrast the percentage of c29 steranes in the extracts correlates with the percentage of higher plant derived vitrinite in the kerogen r2 0 69 and shows a negative correlation with h c ratio and hi r2 0 81 and 0 66 respectively these relationships were used to determine indirectly the source rock kerogen properties of several mowry derived oils the correlations etween biomarkers and source rock properties observed in the aspen shale probably apply to many deltaic and nearshore marine source rocks that were deposited after the evolution of vascular plants therefore prediction of source rock properties from oils in vertically drained basins could prove extremely useful to explorationists seeking to identify the most oil prone areas in regions such as the u s gulf coast the north sea the beaufort sea and the mahakam and niger deltas an example from the beaufort sea is given in this same issue mccaffrey et al 1994

review and update of the applications of organic petrology part 1 geological applications abstract organic petrology developed as coal petrology at the beginning of the 20th century dedicated mainly to the study of coals because of their utilization in industry coal petrology was then considered a branch of coal science later with the development of specialized nomenclature classification of coal components and the standardization and improvement of analytical microscopical methods this discipline expanded in interests and name becoming organic petrology organic petrology carries a broader context being as well a tool applied in the study of dispersed organic matter in sedimentary rocks due to its importance in exploration for fossil fuel resources at present organic petrology is a discipline widely recognized for its role in fundamental and applied research with respect to both coal utilization and in geosciences throughout the 20th century several important monographs have been published on the discipline of organic petrology including stach s textbook of coal petrology 1st edition 1935 2nd 1975 3rd 1982 updated as the more general organic petrology by taylor et al 1998 more recently the text applied coal petrology the role of petrology in coal utilization was published by suarez ruiz and crelling 2008 this review is the first in a two part review series that describes and updates the role of organic petrology in geosciences a second part complementing this one and focused on the applications of organic petrology to other scientific fields will follow

geochemistry of petroleum systems in the eastern pearl river mouth basin evidence for mixed oils abstract detailed analyses of crude oils and source rock extracts indicate the presence of two effective petroleum source rocks in the eastern pearl river mouth basin of the south china sea region oils derived from the lacustrine source rocks in the eocene wenchang formation are characterized by abundant c 30 4 methyl steranes with relatively few c 19 tricyclic terpane and bicadinanes in contrast oils from the eocene oligocene enping formation source typically contain significant amounts of c 19 tricyclic terpane and bicadinanes with relatively few 4 methyl steranes and high pristane phytane ratios however the chemical compositions of a large number of oils do not conform to those of the unknown source rocks consistent with mixing of the two sources mixed oils occur mainly in the huizhou sag and along its south margin and the highest proportion of the enping formation source in the reservoired mixed oils is estimated to be around 80 laboratory mixing experiments using selected end member oils indicate that even with 50 80 contribution from the enping formation source the mixtures still display sterane biomarker ratio signatures diagnostic of the wenchang formation source therefore the presence of abundant 4 methyl steranes is a necessary but not sufficient indicator for the wenchang formation source in the eastern pearl river mouth basin although our results support the wenchang formation as a major source to the known oil discoveries in the study area the contribution of the enping formation source to traps in the huizhou sag and surrounding area cannot be ignored there is clear evidence for the recharge of enping formation derived oils into early biodegraded oil accumulations to form light oil accumulations

characterisation of oil and potential source rocks in the northeastern song hong basin vietnam indications of a lacustrine coal sourced petroleum system oil discovered in the b10 stb 1x well in the northeastern song hong basin vietnam has typical lacustrine coaly geochemical features indicating the existence of a principally lacustrine sourced petroleum system with minor contributions from a coal source the presence of lacustrine source rocks in the basin is indicated by distinct high amplitude seismic reflectors in undrilled half grabens and outcrops of oligocene immature mudstones and humic coals at dong ho and on bach long vi island the mudstones from dong ho generally have a toc content of 8 17 wt and hi values 500 mg hc g toc the organic matter is principally composed of fluorescing amorphous organic matter and liptodetrinite alginite with botryococcus morphology is present the organic matter corresponds to type i kerogen the bach long vi island mudstones contain 2 7 wt toc and have hi values from 200 700 mg hc g toc the organic matter is largely similar to that in the dong ho mudstones but in addition may contain some marine organic material the b10 stb 1x oil shows features common to both the dong ho and bach long vi island mudstones but was probably principally generated from a source similar to the dong ho mudstones with contributions from higher land plant organic matter a prominent activation energy peak dominates the activation energy distributions of the mudstones and upon artificial maturation hydrous pyrolysis the mudstones show extensive hydrocarbon generation over a narrow temperature range hydrocarbon expulsion has been estimated to occur at a vitrinite reflectance of 0 75 ro the source of the b10 stb 1x oil may be located in the thuy nguyen graben and maturity modelling shows that the lacustrine mudstones will be thermally mature in this graben

marine oil source of the yingmaili oilfield in the tarim basin abstract although a large amount of petroleum has been discovered in the tarim basin the origin of the oils is still disputed yingmaili oilfield was selected as a case study to further examine hydrocarbon generation and accumulation in the basin detailed geochemical studies were conducted to unravel the formation mechanisms the oils in the field correlate well with middle upper ordovician o 2 3 rocks or similar rocks oil oil and oil source rock correlation by maturity parameters of saturate and aromatic hydrocarbons suggest that the yingmaili and adjacent oils are primarily comparable to source rocks deeper than 6000 m the results also showed that carbonates might be important potential source rocks as indicated by a relatively high abundance of aromatic sulfur compounds and relatively high c 29 c 30 hopane and c 35 c 34 hopane ratios of the oils which are typical features of carbonate source rocks we suggest the oil from wells yg2 and yg2 1c are more suitable to be end members from the o 2 3 source rocks or similar rocks than the oil from well ym2 as previously suggested we also suggest that the previous model of hydrocarbon migration along the ordovician unconformity should be revised

unstable forearc stress in the eastern nankai subduction zone for the last 2 million years abstract transpressional tectonics characterizes the sw japan arc however we will show in this article that offshore seismic profiles and onshore mesoscale faults indicate that the eastern part of the forearc was subject to transtensional tectonics since ca 2 0 ma offshore normal faults imaged on the profiles run parallel to the nankai trough and started activity at 1 0 ma but transtensional tectonics commenced the onshore area earlier in order to understand the stress history in the forearc region we collected fault slip data from onshore mesoscale faults in plio pleistocene sedimentary rocks in the kakegawa area at the northeastern extension of the offshore normal faults most of the mesoscale faults are oblique normal indicating that the area was subject to transtensional tectonics the faults suggest that the compressional tectonic regime was followed by the transtensional one at 2 0 ma in agreement with regional tectonostratigraphic data which indicate that folding ceased at that time present compressional stress followed the transtensional tectonic regime sometime in the late pleistocene transtensional or extensional tectonic zone shifted from the kakegawa area to the offshore region these observations indicate that the state of stress just behind the accretionary prism of the eastern nankai subduction zone has been unstable in the last 2 million years suggesting that the forearc wedge has been at critical state in that gravitational force and basal shear traction on the wedge have been balanced but the forearc tectonics has been susceptible to small perturbations possible factors compatible with the observed stress history include the change of subduction direction of the plate at 1 0 ma and the rapid uplift of central japan thereafter

body wave crustal attenuation characteristics in the garhwal himalaya india we estimate frequency dependent attenuation of p and s waves in garhwal himalaya using the extended coda normalization method for the central frequencies 1 5 2 3 4 6 8 10 12 and 16 hz with earthquake hypocentral distance ranging from 27 to 200 km forty well located local earthquake waveforms were used to study the seismic attenuation characteristics of the garhwal himalaya india as recorded by eight stations operated by wadia institute of himalayan geology dehradun india from 2007 to 2012 we find frequency dependent p and s wave quality factors as defined by the relations q p 56 8f 0 91 0 002 and q s 151 8f 0 84 0 002 by fitting a power law frequency dependence model for the estimated values over the whole region both the q p and q s values indicate strong attenuation in the crust of garhwal himalaya the ratio of q s q p 1 obtained for the entire analyzed frequency range suggests that the scattering loss is due to a random and high degree of heterogeneities in the earth medium playing an important role in seismic wave attenuation in the himalayan crust

izu bonin arc subduction under the honshu island japan evidence from geological and seismological aspect abstract the izu bonin intra oceanic arc with 20 35 km thick continental crust is being subducted under the honshu presumably since 17 ma tomographic image clearly demonstrates that the whole izu bonin arc is subducting under the honshu arc geologic cross section and the thickness of continental crust do not support the accretion of thick crust in spite of the continued subduction over 17 ma

strain partitioning between the suruga trough and the zenisu thrust neogene to present tectonic evolution in the onland and offshore tokai district japan abstract the tokai district in central japan is located close to the convergent boundary between the philippine sea and eurasian plates and has experienced not only repeated large interplate earthquakes but also intense aseismic movement in this paper the spatial and temporal tectonic evolution of the tokai district particularly around the omaezaki area is discussed to assess whether the district has been and will be active or inactive according to a geological survey the horizontal crustal shortening strain can imply the hypothetical tectonic model that the area has been getting less active and the strain rate since the neogene can be calculated as 12 and 2 10 6 year respectively the present interseismic horizontal crustal strain and strain rate around the omaezaki area are approximately 4 10 7 and 4 10 9 year by comparing these rates the decrease since neogene can imply the hypothetical tectonic model that the area has been getting less active influenced by the strain partitioning between the suruga trough and the zenisu thrust

seismic activity changes progressing simultaneously with slow slip in the tokai area abstract anomalous movements were detected simultaneously in both the seismic and the gps observations in the tokai area the central part of the japanese islands from the late 1990s to 2000 the anomalies are of great concern since the pending risk of a large megathrust earthquake in this area has been predicted for more than 20 years the gps data revealed that a slow slip on the plate interface had commenced beneath lake hamana the center of which is positioned around the edge of the assumed focal zone on the other hand the seismic data indicated that a delicate but clear quiescence appeared over a wide area that spreads into the main focal zone analyses of the seismicity changes in space and time confirmed that the contrast in the seismicity rate is distinct inside the focal zone while the integrated seismicity indicated quiescence some locations were distinguished as activated zones possibly indicating the appearance of asperities the rise of the seismicity rate in a quasi stationary manner suggests an increase in the stress rate at that location the following hypothesis is proposed based on the simultaneously detected evidences the slow slip progressing beneath lake hamana will induce a stress shift that invades the interior of the main locked zone which will increase the contrast of the seismicity rate possibly reflecting inhomogeneity in the locking strength even in this stage the activated zones still maintain a locked state to prevent overall breakage investigations of the b value changes and of tidal dependence in seismicity that reveal the stress concentrated state also support the hypothesis if this is the case the observed change in seismicity would indicate the process of stress redistribution in the locking state which represents the preparatory process toward final breakage tracking such seismicity changes would yield valid information for predictions of the next tokai earthquake

cause of m 7 intraslab earthquakes beneath the tokyo metropolitan area japan possible evidence for a vertical tear at the easternmost portion of the philippine sea slab 1 we perform travel time tomography beneath kanto japan to obtain detailed structures of the wedge shaped serpentinized mantle previously observed in the philippine sea slab the results suggest that the western boundary of the serpentinized mantle serpentine boundary is subvertical and p and s wave velocities vary by 15 20 across it over the short distance of 10 km two intraslab earthquakes in 1921 m7 0 and 1987 east off chiba earthquake m6 7 are inferred to have occurred along the serpentine boundary accompanied by right lateral movement based on analyses of focal mechanisms and aftershock distribution a subvertical earthquake cluster penetrating the entire philippine sea slab is observed along the serpentine boundary and four earthquakes in the cluster have strike slip focal mechanisms similar to that of the 1987 earthquake focal mechanisms obtained for past large earthquakes and present day microearthquakes suggest a concentration of right lateral deformation along the mechanically weak serpentine boundary the philippine sea slab may have been torn in two along this boundary with the eastern portion being left behind relative to subduction of the western portion assuming that one of the large aftershocks m7 1 of the 1923 kanto earthquake m7 9 which occurred off the boso peninsula ruptured the same asperity as did the 1987 earthquake the slip deficit accumulated along the serpentine boundary during the 64 year interval is consistent with the fault slip of the 1987 earthquake interaction between the seismic slip along the plate interface and the serpentine boundary can explain the series of m7 class earthquakes before and after the 1923 kanto earthquake

interplate coupling in the kanto district central japan deduced from geodetic data inversion and its tectonic implications abstract interplate coupling between the philippine sea phs the north american nam and the pacific pac plates in the kanto district central japan has been investigated through the inversion analysis of geodetic data using akaike s bayesian information criterion abic the data used for the analysis are annual rates of level changes 1972 1985 and horizontal length changes 1973 1990 which presumably represent average crustal movements during the interseismic period disregarding effects of steady plate subduction we may ascribe the observed crustal movements to the effects of locking or faulting on some parts of the plate boundaries in our model the effect of locking is represented by back slip on the plate boundary and that of faulting by forward slip the results of the inversion analysis show the existence of a strongly coupled area on the southwestern shallower part of the nam phs plate boundary which almost coincides with the faulting area of the 1923 kanto earthquake m 7 9 and a notable faulting area on the northeastern deeper part of the phs pac plate boundary in the southwestern strongly coupled area the rate of back slip reaches 3 5 cm yr and its direction is oriented n33 w which is almost opposite to the direction of fault slip s29 e at the time of the 1923 event this suggests that tectonic stress accumulation for the next large event is effectively proceeding there and its recurrence time is roughly estimated as 245 years the strongly coupled region is also recognized as corresponding to a recent seismic gap the inverted forward slip distribution on the phs pac plate boundary which has the average rate of 1 9 cm yr and the average direction of n56 e may be explained by aseismic northeastward slip in relation to the process to form a peculiar configuration of downward bend of the phs plate beneath the kanto district

petroleum generation and migration from talang akar coals and shales offshore n w java indonesia abstract the oligocene talang akar formation is the major source for petroleum oil and gas in the ardjuna sub basin source rock quality varies within the deltaic to marginal marine complex with coals deposited on the lower delta plain being distinctly oil prone whereas the surrounding delta plain shales are largely gas prone shales and drifted coals laid down in marine influenced interdistributary bay environments show increasingly oil prone characteristics possibly due to preferential transport of hydrogen rich plant components to more distal setting molecular characteristics of the coals and shales are similar with higher plant angiosperm biomarkers and their aromatic derivatives occuring widely kinetic studies of hydrocarbon generation and stimulated maturation experiments using hydrous pyrolysis indicate that the delta plain coals are the major source for crude oils in the basin with a secondary but minor contribution from marine influenced interdistributary bay shales delta plain shales are interpreted to expel gaseous products only the stratigraphic and spatial location of oil and gas fields were examined with respect to their position relative to oil and gas generating source rocks the field distribution could not be explained in terms of source rock geochemistry alone and phase behavior of petroleum during secondary migration was shown to exert an important influence on the distribution of oil and gas deposits in the basin

transportation of h2o beneath the japan arcs and its implications for global water circulation abstract in order to understand the transportation and circulation of h2o in subduction zones geological and seismological observations and the corresponding quantitative modeling are reviewed and consolidated with a special emphasis on the japan arcs the japan arcs are ideal for such a study in that 1 they are very active magmatically and seismically with abundant high quality observations and 2 subduction parameters change significantly along the japan arcs allowing one to investigate how the variations of input parameters affect the resultant structures and processes first numerical models for the transportation of h2o and melting are introduced the generation and migration of aqueous fluid its interaction with the convecting solid and melting are considered based on the realistic phase relationships of the peridotitic and basaltic systems application of the models to the japan arcs and comparison between the model results and the observations distribution of volcanoes and seismic structures along the japan arcs are then discussed the three cases from the ne central and sw japan arcs clarify the following points first an aqueous fluid released from the subducting oceanic crust forms a serpentinite layer in the mantle wedge just above the subducting slab maintaining a condition close to equilibrium in terms of hydration dehydration reactions during aqueous fluid migration second most of the h2o is subducted to a depth where serpentine and chlorite in the serpentinite layer break down this depth depends on the thermal structure of the slab and is greater for the older plate beneath the japan arcs as a consequence aqueous fluid and melt are in general not supplied straight upward to the volcanic front this result is rather different from the conventional view finally based on the understanding obtained from the japan arcs the global budget and circulation of h2o are discussed even after the completion of dehydration of major hydrous mineral phases in the subducting materials especially at the base of the mantle wedge just above the subducting slab nominally anhydrous phases of the upper mantle assemblage i e olivine pyroxenes garnet can carry a significant amount of h2o 1 1 1011 to 7 8 1011 kg yr 1 into the deep mantle the minimum estimate is comparable to the outflow of h2o from the mantle at mid ocean ridges and hotspots while the maximum estimate greatly exceeds it the large estimated range is mainly due to the uncertainty of the maximum h2o contents in the nominally anhydrous minerals of the upper mantle which controls the net influx of h2o into the deep mantle through subduction zones water subduction magmatism global circulation

a slab fragment wedged under tokyo and its tectonic and seismic implications a three dimensional evaluation of earthquake hypocentres beneath the kanto basin in japan reveals the presence of a distinct 25 km thick and 100 km wide body its fast seismic velocity and the presence of a double seismic zone suggest that it is a fragment of the pacific slab rather than an extension of the philippine sea slab this implies that the penetration of the philippine sea slab is much shallower beneath the kanto basin than was previously thought the philippine sea and pacific plate slabs both subduct beneath tokyo and so their configuration and seismic potential have been subject to intensive study1 2 3 4 5 6 7 8 previous work suggests that the philippine sea slab extends up to 100 km northwest of tokyo and subducts to a depth of 90 km beneath the kanto basin where it is folded against the underlying pacific slab here we evaluate seismic data in three dimensions and delineate a distinct 25 km thick and 100 km wide body beneath the kanto basin that has hitherto been considered to be part of the philippine sea slab we find that several of its characteristics such as its high seismic velocity and the presence of a double seismic zone point instead to an affinity with the pacific slab implying that the philippine sea slab penetrates to depths of only 35 40 km beneath the kanto basin we propose that the body is a fragment of pacific lithosphere that formed by the collision of two intersecting seamount chains with the japan trench 2 3 million years ago we suggest that such slab fragments may not be uncommon especially where seamount subduction deforms trenches and near triple junctions

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

an andean model of interplate coupling and strain partitioning applied to the flat subduction zone of sw japan nankai trough abstract transcurrent motion is commonly observed in cases of oblique subduction yet the causes remain controversial a model of increased interplate coupling linked to flat subduction is proposed as a mechanism for producing strain partitioning at a great distance several hundred km from the trench the model originally developed for the north andean margin is applied to the geodynamics of sw japan here along the nankai trough and below adjacent sw honshu flat subduction occurs due to the relatively young age m 7 and nine additional m 6 earthquakes in the past 300 years dextral strike slip focal mechanisms for 15 modern and historical events indicate a significant degree of subduction related strain partitioning manifested by right lateral strike slip faulting along the adakitic volcanic arc some 400 km from the nankai trough

correlating seismicity parameters and subsidence in the tokai region central japan 1 we demonstrate that transients in subsidence rate in the tokai area of central japan correlate with changes in the rate and size distribution of earthquakes three largely independent seismic catalogs cover this region national research institute for earth science and disaster prevention nied japanese meteorological agency jma and japan university network catalog junec comparing seismicity patterns between these three data sets offers a unique opportunity to verify seismicity anomalies based on independent sources a study of data quality magnitude reporting consistency and consistency across the three data sources reveals that the nied data for the period 1981 2002 are best suited for seismicity analysis we spatially and temporally map seismicity rates finding that a significant decrease in the earthquake rate of m 2 0 events coincides with an accelerated subsidence period however this anomaly disappears when including smaller magnitudes in the analysis this relative quiescence of larger events can readily be explained when interpreting the transient in seismicity in the framework of a change in the earthquake size distribution or b value the background b value of about 0 8 increased in the period 1987 5 1989 5 to a value of b 1 2 a highly significant change that can be confirmed in all three data sets the correlation between subsidence and b value change is significant stress tensor inversions of focal mechanism data for the anomalous period show an increase in thrusting type earthquakes while a unique interpretation of the relationship between subsidence and b value is not possible we propose that an increase in the locking stress a slow stick event is consistent with all observations

estimates of regional and local strong motions during the great 1923 kanto japan earthquake ms 8 2 part 2 forward simulation of seismograms using variable slip rupture models and estimation of near fault long period ground motions abstract this article addresses the forward simulation of regional and local strong motions from the 1923 kanto japan earthquake ms 8 2 using two variable slip rupture models the wald and somerville 1995 slip model ws slip model derived from geodetic and teleseismic data and a resampled version of the takeo and kanamori 1992 slip model tk slip model that was obtained from the forward simulation of the ewing seismoscope record at hongo hng epicentral distance r 60 km green9s functions are calculated using flat layered velocity models for specific source receiver paths which were developed in our first article sato et al 1998 for regional stations sendai r 350 km and gifu r 220 km the ws slip model provides a much better match to the waveform data than the tk slip model for local station hng the first 40 sec of the n77 e imamura seismogram is successfully reproduced by both of the slip models although the arrivals are delayed in the tk slip model the large amplitude long duration long period 13 sec later phases in the southwest component ewing seismogram are not reproduced by either of the slip models our results suggest that the ws slip model gives a better representation of the overall rupture process of the 1923 event than the tk slip model does near fault long period ground motions calculated at several stations using the ws slip model suggest that the motions at hng were not the largest in the tokyo metropolitan area during the 1923 event in addition we estimate that the ground motions near the southern margin of the fault plane were significantly larger than the recorded near fault motions of recent magnitude 7 earthquakes such as northridge and kobe for periods longer than several seconds this suggests that design codes based on the experience of these recent events may not adequately describe the long period response expected during a magnitude 8 earthquake

the seismically quiescent boundary between the philippine sea plate and the eurasian plate in central japan abstract the boundary between the philippine sea phs and eurasian eur plates which is presently seismically quiescent is delineated on the basis of seismological data from the kanto tokai k t district during the period from january 1980 to april 1993 most of the earthquakes in the k t district occur either in the overriding plate the eur plate or within the subducting slab the phs plate at depths of less than around 30 km the plate boundary between the phs and eur plates is characterized by a very low level of seismic activity i e the plate boundary itself is presently seismically quiescent and the seismicity consists of intra plate events above or below the plate boundaries in the tokai district earthquakes in the overriding eur plate are mostly characterized by strike slip faulting with an e w directed compressional axis while those within the subducting phs slab are characterized by strike slip faulting with a n s directed compressional axis in the kanto district the earthquakes are mostly characterized by faults with nw se directed compressional axes the above difference between the tokai and kanto districts is thought to be due to the difference in the slab configuration and or regional stress conditions considering the results of the present paper together with geodetic data the seismically quiescent plate boundary at depths from 10 to 30 km suggests strong coupling between the phs and eur plates and is consistent with strain accumulation during an inter seismic period

subduction process of the philippine sea plate off the kanto district central japan as revealed by plate structure and repeating earthquakes abstract the structure of the philippine sea plate in the offshore region adjacent to the boso peninsula in central japan is resolved by comparison of recent oceanic seismic survey data with natural repeating earthquake data this region is characterized by a range of seismic and aseismic phenomena associated with subduction motion of the philippine sea plate including slow slip events sses large backslip events and repeating earthquakes this offshore region is also the site of the largest aftershock of the 1923 kanto earthquake m7 9 the detailed structure of the philippine sea plate is successfully resolved and the upper boundary of plate is clearly traceable to depths of 20 km the reflection intensity of the upper boundary varies spatially in accordance with the depth of the reflector the upper boundary continues smoothly with a line of repeating earthquake hypocenters regarded as an indicator of subduction shear a continuous model extending into the offshore region can thus be proposed the variation in reflection intensity on the upper boundary of the philippine sea plate also correlates well with variation in event types a weak reflection zone overlaps the area of large backslip while a moderately strong reflection zone encroaches into the large slip area of the boso sse the reflectivity of the upper boundary is thus considered to be dependent on the physical properties and conditions of the reflector which in turn affect the event types on the plate boundary a source fault model is proposed for the largest aftershock of the 1923 kanto earthquake based on geodetic data the source fault is located eastward of the mainshock with dimensions of 40 50 km and moment magnitude of 7 5 the source fault lies within the region of large backslip and the large slip area of the boso sse

crustal deformation and stress localization in kanto tokai central japan revealed by gps summary horizontal deformation associated with plate interaction in the kanto tokai district central japan has been determined using the japanese permanent global positioning system gps array with an accuracy of better than 2 5 mm yr 1 previous analysis of the gps observations mainly focused on the pattern of deformation or strain and did not attempt to assess stress change associated with plate subduction in this study using the gps observations and the geometry of subducting slabs as constraints we constructed a 3 d kinematic model to simulate the subduction of the philippine sea plate at the suruga and sagami troughs and the pacific plate at the japan trench the model incorporating the effects of major plate driving forces ridge push slab pull and drag force associated with plate subduction provides an overall fit to the horizontal deformation observed by gps during 1996 2001 in the kanto tokai region the horizontal motion of the philippine sea plate is estimated to be 41 5m m yr 1 60 5 nw consistent with that ca 43 50 mm yr 1 inferred from earthquake slip vectors and geological data the horizontal motion of the pacific plate is estimated to be 78 6m m yr 1 84 5 nw close to that ca 73 79 mm yr 1 deduced from earthquake slip vectors after extracting the regional deformation associated with subduction of the philippine sea and pacific plates from the gps observations two types of motion trends are revealed for the northern part of the kanto tokai region the southeastward motion of the gps stations revealed by the residual displacements in northern tokai indicates a possible resistance force from the north in northern kanto the west southwestward residual motion of the gps stations indicates the motion of the north american plate relative to the eurasian plate the distinct boundary between these two different types of motion trends provides strong support for the presence of the north american plate in the region which demonstrates that the model has delineated the main characteristics of plate interaction further a stress analysis indicates that stress is accumulating on the suruga trough at a rate of approximately 0 7 bar yr 1 at a depth of 15 km our results indicate that the pattern of stress localization is mainly controlled by the kinematic characteristics of the subducted slabs geometry and slip distribution and the persistent stress concentration is responsible for repeated large interplate earthquakes in the region

crustal velocity field of southwest japan subduction and arc arc collision we investigate crustal deformation in southwest japan over a 3 year period revealed by a permanent dense global positioning system gps array southwest japan is a part of the amurian plate a microplate moving about 10 mm yr toward the east with respect to the eurasian plate it overrides the philippine sea plate at the nankai trough and collides with the northeast japan arc in the central part of japan in this paper we first derive gps site velocities relative to the stable part of the amurian plate in order to isolate signals of crustal deformation caused by the subduction and or the collision the velocity field has a conspicuous feature indicating the interseismic elastic loading by the philippine sea plate slab at the nankai trough characterized by the northwestward movements of points throughout the studied area their amplitudes are the largest at the pacific coast and decay toward the japan sea coast with a subtle systematic shift of azimuths a model assuming an elastic half space the convergence rate at the nankai trough based on a refined euler vector and the strength of the coupling inferred from a thermal model could explain the velocity field in the western part of the studied area to a large extent those in the eastern part systematically deviate from them and the residual components there show east west shortening and north south extension this may represent crustal thickening and trenchward extrusion of crustal blocks caused by the collision between southwest and northeast japan this suggests that the collision between southwest and northeast japan gives rise to not only crustal thickening but also trenchward extrusion of crustal block a velocity contrast was found across the median tectonic line the largest inland active fault in japan but the current permanent gps network is not dense enough for us to discuss its coupling depth

geometry and relative motion of the philippine sea plate and pacific plate beneath the kanto tokai district japan the recent acquisition of high density and improved seismic data by the kanto tokai k t observational network of the national research institute of earth science and disaster prevention requires the revision of conventional plate configuration models for the k t district we propose a new interpretation of the configuration and relative motion of the philippine sea phs plate pacific pac plate and eurasian eur plate on the basis of the distribution of hypocenters velocity structure and focal mechanisms in the k t district the new model for the configuration of the phs and pac slabs clearly delineates the phs slab subducting northwestward beneath the k t district from the sagami and suruga troughs and the pac slab subducting westward beneath the phs slab from the japan trench the thickness of the descending phs slab is estimated to be 30 5 km the proposed configuration of the phs slab is significantly different from those obtained by other researchers including our own previous study the new model is fully consistent with global plate motion data the new model leads to an interpretation of the tectonic processes taking place beneath the k t district for the sagami trough wing of the phs slab the northeastern portion of the slab is dipping northwestward in direct contact with the upper surface of the pac slab the southwestern portion carrying the izu peninsula has been bent upward because of its buoyancy producing the observed contorted shape for the suruga trough wing the dip direction of the phs slab gradually changes from northwestward at the eastern portion to northward at the western portion the new model also indicates the presence of offset within the phs slab between the sagami and suruga trough wings this area is characterized by a low level of seismic activity the absence of a high velocity structure and the presence of quaternary volcanoes it seems reasonable to speculate that the distribution of quaternary volcanic edifice construction is controlled by the location of the offset within the phs slab in view of this new model the tectonic processes of large earthquakes which occurred recently in the studied area are also reexamined

the 1923 kanto earthquake reevaluated using a newly augmented geodetic data set 1 this study revisits the mechanism of the 1923 ms 7 9 kanto earthquake in japan we derive a new source model and use it to assess quantitative and qualitative aspects of the accommodation of plate motion in the kanto region we use a new geodetic data set that consists of displacements from leveling and angle changes from triangulation measurements obtained in surveys between 1883 and 1927 two unique aspects of our analysis are the inclusion of a large number of second order triangulation measurements and the application of a correction to remove interseismic deformation the geometry of the fault planes is adopted from a recent seismic reflection study of the kanto region we evaluate the minimum complexity necessary in the model to fit the data optimally our final uniform slip elastic dislocation model consists of two adjacent 20 dipping low angle planes accommodating reverse dextral slip of 6 0 m on the larger eastern plane and 9 5 m on the smaller western plane with azimuths of 163 and 121 respectively the earthquake was located in the sagami trough where the philippine sea plate subducts under honshu compared to the highly oblique angle of plate convergence the coseismic slip on the large fault plane has a more orthogonal orientation to the strike of the plate boundary suggesting that slip partitioning plays a role in accommodation of plate motion what other structure is involved in the partitioning is unclear uplift records of marine coastal terraces in sagami bay document 7500 years of earthquake activity and predict average recurrence intervals of 400 years for events with vertical displacement profiles similar to those of the 1923 earthquake this means that the average slip deficit per recurrence interval is 50 of the relative plate convergence these findings of plate motion partitioning and slip deficit lead us to suggest that instead of a simple recurrence model with characteristic earthquakes additional mechanisms are necessary to describe the accommodation of deformation in the kanto region so far obvious candidates for these alternative mechanisms have not been discovered

integrated study of the judy field block 30 7a an overpressured central north sea oil gas field the triassic reservoirs of the judy field an overpressured petroleum accumulation in the central north sea have been studied to determine their pressure and petroleum filling history the magnitude of overpressure in the pre cretaceous aquifer is similar across the field at about 24 mpa 3500 psi but with some higher pressure laterally in areas closest to the major depocentres pressure modelling shows that the magnitude of the overpressure can be attributed almost entirely to disequilibrium compaction and largely due to late rapid tertiary burial although modelling does require nanodarcy i e shale like permeability in the cretaceous chalk section the contributions from other mechanisms which may be relevant in this setting i e gas generation and lateral transfer appear to be small the existence of both aqueous and petroleum phases in secondary fluid inclusions in microfractures in quartz and feldspar grains allows estimation of palaeopressure the data show fracture healing from 115 to 136 c during a time when reservoir palaeopressures were above hydrostatic reconstruction of the temperature history of the reservoir places the timing of the fluid inclusion formation during fracture healing at between 3 and 1 my ago coincident with a period of rapid burial the palaeopressure estimation using fluid inclusions validates the pressure modelling studies which are derived independently from commercial basin modelling software the fluid inclusions also revealed a low gor oil over the whole field prior to late stage flooding by gas leading to the variable low to high gor fluids plus gas condensates within the field today

interplate coupling and relative plate motion in the tokai district central japan deduced from geodetic data inversion using abic summary the spatial distribution of the strength of interplate coupling between the subducting philippine sea and overlying continental plates in the tokai district central japan was investigated in detail through the inversion analysis of geodetic data using akaike s bayesian information criterion abic the geodetic data used for the analysis are annual rates of level changes 1972 1984 and horizontal length changes 1977 1988 which presumably represent average crustal movements during the interseismic period the result of the inversion analysis shows the existence of a strongly coupled region extending from 10 to 30 km in depth the total seismic moment accumulated in this area since the last event the 1854 ansei earthquake is roughly estimated to be 5 5 1027 dyne cm which corresponds to ms 7 8 the interplate coupling becomes weaker toward the shallower and deeper portions this is consistent in general tendency with a rheological model inferred from petrological viewpoints the strength of coupling also tends to decrease toward northeast over the west coast of suruga bay the direction of plate convergence inferred from the inversion analysis is oriented n30 w this is significantly different from the direction of relative plate motion between the philippine sea and eurasian plates but concordant with that between the philippine sea and north american plates

episodic basin wide hydrofracturing of overpressured early cenozoic mudrock sequences in the north sea basin a deformational fabric associated with the early cenozoic mudrock dominated sequences of the north sea is described seismic data show that the mudrock sequences are pervasively faulted over a large area of the basin axis in the central and northern north sea mapping the faults using regional two and three dimensional data shows that the faults are minor extensional structures arranged in stratigraphically bound tiers in the deep water sequences and bounded by regional condensed sequences seals the geometry of the faulting is complex faults are organized into cellular networks comprising polygonal prismatic and pyramidal forms a gravitational mechanism of downslope collapse faulting is rejected on the grounds that the distribution of the deformed sequences extends over large areas of formerly horizontal basin plain a mechanism involving the repeated development of basin wide overpressured compartments is proposed in which the cellular structure is related to deformation patterns associated with a density inversion between the overpressured units and the overlying seal hydrofracturing is invoked to account for the almost random strike distribution of the faulting the region affected by the pervasive fluid expulsion faulting encompasses almost half of the north sea basin basin wide collapse of the overpressured compartments could have resulted in a geologically rapid flux of enormous volumes of pore fluids this mechanism has implications for concepts of steady state compaction heat flow in basins hydrocarbon transport and the genesis of lead zinc ore deposits

earthquake of 1987 off chiba central japan and possible triggering of eastern tokyo earthquake of 1988 abstract a moderate earthquake m 6 7 occurred off eastern chiba central japan on december 17 1987 as a consequence of the internal deformation of the philippine sea plate this event helped in clarifying the geometry of the easternmost part of the philippine sea plate as well as the mode of earthquake occurrence in this region three months later another moderate earthquake m 6 0 took plate beneath eastern tokyo this event was generated at the slab slab collision zone at about 90 km depth and is considered to be triggered by the former earthquake a similar phenomenon was observed for the izu m 6 7 of june 29 1980 and the mid chiba m 6 1 of september 25 1980 earthquake pair and the off ibaraki m 7 0 of july 23 1982 and the southern ibaraki m 6 0 of february 27 1983 earthquake pair these are the only three earthquake pairs of m 6 which occurred in the tokyo metropolitan area since 1974 thus over these 15 years all m 6 interplate earthquakes in this specific region are preceded by nearby m 7 earthquakes this suggests that m 7 shallow events enhance stress in the deeper plate collision zone beneath the tokyo metropolitan area and trigger m 6 interplate events

characterization of hydrothermally generated oil from the uzon caldera kamchatka abstract this paper reports the analyses of unusual oils that accumulate in the uzon caldera situated in the central volcanic region of kamchatka russia gas chromatography mass spectrometry gc ms was used to determine the primary constituents and the 13 c and 14 c compositions provided information about the potential source and age of the oils the 14 c ages determined are 1030 40 a bp measured or 940 40 a bp conventional the 13 c value is 30 6 versus the pdb standard a value consistent with a biological origin the nearly contemporary age of the c content indicates a geologically recent origin from biogenic detritus and not by synthesis from mantle c the biogenic origin is supported by the presence of sterane and hopane biomarkers and the 13 c value of the bulk oil the overall compositions of the oils indicate that they are derived from rapid hydrothermal alteration of algal bacterial mat detritus buried by volcanic ashfall deposits of the uzon caldera the oils represent the youngest hydrothermal petroleum reported to date

focal zone of a future tokai earthquake inferred from the seismicity pattern around the plate interface abstract a future large tokai earthquake has been considered to be the most urgent problem of impending disasters in the central part of the japanese islands since the first warning was announced in 1976 recent progress in observations has provided a great amount of data thus making a detailed investigation possible in this study based on the seismicity and the focal mechanism patterns of microearthquake data the mechanical situation that governs plate interactions around the tokai district was investigated it was found that the seismicity in the subducting philippine sea slab is composed of three characteristic groups of activities intense activity beneath lake hamana a linear cluster extending from lake hamana toward the northwest and a broad cluster expanding over the inland area in the west of suruga bay we propose that these activities occur inside the subducting oceanic crust and reflect the present stress state acting there the mechanism inducing these activities is assumed to come from two stress sources the lateral stretching of the slab and the partial locking between both plates this interpretation leads to the hypothesis that the broad cluster in the west of suruga bay represents a stress concentration due to locking the activity beneath lake hamana is proposed to represent shearing motion induced there and is interpreted to form the boundary between the rupture zones of the 1944 tonankai earthquake and a future large tokai earthquake these analyses resulted in identifying the wide inland area extending from the west coast of suruga bay to lake hamana to be a focal zone of a future tokai earthquake the zone proposed in this study indicates a significant deviation in its strike from the original model proposed by ishibashi in that the former parallels the nankai trough while the latter parallels the suruga trough

deep seismic imaging of the eastern nankai trough japan from multifold ocean bottom seismometer data by combined travel time tomography and prestack depth migration 1 the easternmost segment of the nankai trough remained unruptured during the 1944 and 1946 earthquakes that affected the rest of the trench it is therefore a zone of seismic gap that also undergoes a peculiar tectonic regime due to its proximity with the izu collision zone we investigate this area with densely sampled active seismic data one hundred ocean bottom seismometers spaced only 1 km apart were deployed along a line perpendicular to the trough a two step tomographic approach designed for this type of acquisition is applied first a long wavelength velocity model is built by a linearized inversion of first arrival travel times its resolution is assessed and its reliability is confirmed through a semiglobal approach in which a large range of starting models is tested second this tomographic model is used to exploit late reflected arrivals with a prestack depth migration the result of which is validated by classically modeling refraction and reflection travel times in the derived structural model thus both velocities and discontinuities are mapped in our model with a minimum of data interpretation and a priori knowledge our results bring new insights on the deep crustal zones of the margin and its evolution the existence of presently inactivated major thrusts is very clearly evidenced in the backstop a general timing for its evolution and deformation is proposed farther seaward the presence of a subducted ridge beneath the accretionary wedge is confirmed its compressive structure and origin are demonstrated it exhibits a thickened lower crust which nature is discussed besides strong analogies between this paleo zenisu subducting ridge and the zenisu ridge observed farther south are also emphasized bringing evidences for a steady state crustal deformation pattern