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Oda M.,Tohoku University | Chiyonobu S.,Tohoku University | Chiyonobu S.,Japan Research Institute of Innovative Technology for the Earth | Torii M.,Kumamoto Gakuen University | And 6 more authors.
Journal of Asian Earth Sciences | Year: 2011

An integrated magnetobiochronology of the Miyazaki Pliocene-Pleistocene succession in the Miyazaki area, southwest Japan, was established using planktic foraminiferal and calcareous nannofossil biostratigraphy together with paleomagnetic data. The upper Miyazaki succession in the northern Miyazaki region can be divided into the Takanabe, Hisamine (redefined), and Higoyashiki (new) Formations, in ascending order. A depositional hiatus between the Hisamine Formation and the Takanabe and/or older formations was also identified based on integrated magnetobiostratigraphy from five sections including the Nagatani River (NGT) section through the uppermost Miyazaki succession. The hiatus, herein called the Hisamine unconformity, is equivalent to the Kurotaki unconformity between the Miura and Kazusa groups of the Boso Peninsula in central Japan. The depositional hiatus recognised in the lower Pleistocene of Pacific coastal areas in southwestern and central Japan may have resulted from tectonic activity associated with a change in the subduction direction of the Philippine Sea plate, which commenced prior to ca 2.2 Ma. The youngest unit just below the hiatus is the upper part of the Takanabe Formation in the NGT section. The NGT section represents the continuous Late Pliocene to earliest Pleistocene sequence including the Gauss/Matuyama boundary and is here proposed as the type section for the Pliocene/Pleistocene boundary in Japan, which the IUGS ratified as the base of the Gelasian in 2009. © 2010 Elsevier Ltd.


Fukuda K.,Mitsui Oil Exploration Co. | Suzuki M.,Yachimata City | Ito M.,Chiba University
Sedimentary Geology | Year: 2015

This study investigates the internal geometry and formation processes of submarine-slide deposits in a lower Pleistocene outer-fan succession in the Kazusa forearc basin on the Boso Peninsula of Japan. The submarine-slide deposits are ~. 40. m thick, with a minimum length of ~. 900. m and a width of ~. 700. m. Both the submarine-slide deposits and host deposits comprise siltstones intercalated with very thin- to medium-bedded, sheet-like turbidites and volcanic ash beds. Based on the sequence-stratigraphic framework of the submarine-fan succession, we conclude that the submarine-slide deposits formed during a glacioeustatic sea-level lowstand at about 1.16. Ma.The submarine-slide deposits are characterized by thrust sequences with a ramp anticline in the frontal part. A basal slide plane in the lower part of the deposits is developed at a horizon located 2-4. cm below the base of a coarse volcanic ash bed and is associated with sheared deposits. Slide planes are sealed in the upper part of the submarine-slide deposits in association with drag folds and chaotic deposits. Finally, the submarine-slide deposits are transitionally overlain by ~. 3-m-thick chaotic muddy deposits, and are finally overlain by siltstones intercalated with very thin- to medium-bedded, sheet-like turbidites and volcanic ash beds, which show lithofacies features similar to those of the submarine-slide deposits. The variations in the deformation styles indicate that sliding occurred as a synsedimentary process in the outer-fan environment, and the basal slide plane formed when the porosity of the muddy deposits was reduced to ~. 55% or less.Based on the empirical relationship between the submarine-fan length and lower-fan slopes from modern examples, the gradient of the outer-fan is estimated at 0.31°-0.46°, which is lower than the threshold gradient of 1.2° for a 40-m-thick submarine slide with the estimated basal porosity. Based on the distribution of deformed deposits within the lower-fan host deposits, the minimum volume and runout distance of the submarine-slide deposits are estimated to be ~3×107m3 and ~5km, respectively. Furthermore, based on data from modern submarine slides, the elevation difference between the failed mass in both the starting and depositional areas is estimated to be 80-170m. Thus, the initiation of a submarine slide in the outer-fan environment was likely influenced by a combination of external forces, such as seismic shaking and increased pore-water pressure in association with the seepage of gas and water from underlying deposits in the Kazusa forearc basin. This study suggests that submarine slides occur in distal and low-gradient deep-water environments in active-margin basins. © 2015 Elsevier B.V.


Eto T.,Tohoku University | Asanuma H.,Japan National Institute of Advanced Industrial Science and Technology | Adachi M.,INPEX Corporation | Saeki K.,Okuaizu Geothermal Co. | And 4 more authors.
Transactions - Geothermal Resources Council | Year: 2013

The occurrence of induced seismicity in the form of felt earthquakes has been recognized as one of the critical environmental burdens associated with recent geothermal development. For this reason, research into enabling technologies for risk assessment of larger magnitude induced events has taken on an increased priority. In this study, we have applied a seismostatistical modeling method to microseismic data collected at two geothermal fields and have investigated its feasibility for risk assessment. Here we have applied the Epidemic Type Aftershock Sequence (ETAS) model (Ogata, 1988), which has been widely used in the area of natural seismology, as a first step in this geothermal earthquake risk assessment study. The microseismicity observed at Yanaizu-Nishiyama, one of the largest hydrothermal geothermal fields in Japan, has been successfully modeled with ETAS. Induced seismicity at the Basel EGS site in Switzerland was also modeled with ETAS, in this case using short moving time windows since modeling for the whole seismically active period was unsuccessful. Our study suggests that one of the parameters in the ETAS model, which has previously been interpreted to represent the occurrence rate of events triggered by external forcing (Hainzl and Ogata, 2005), can in both our cases be correlated with the treatment/stimulation injection rate into each reservoir. Our preliminary results demonstrate the feasibility of seismostatistical modeling in assessing the risks of felt earthquakes associated with various human operations in geothermal reservoirs, although further investigation and modeling of behavior of induced seismicity is required.


Morimoto J.,Mitsui Oil Exploration Co. | Oda M.,Sendai University | Torii M.,Kumamoto Gakuen University | Chiyonobu S.,Sendai University | And 2 more authors.
Stratigraphy | Year: 2010

Neogene sedimentary deposits are present in the Miyazaki region, southern Kyushu, on the Pacific side of southwestern Japan. The upper part of the Miyazaki Group, exposed in the Tsuma-Takanabe region of northern Miyazaki, is divided into the Tsuma, Sadowara, and Takanabe formations, in ascending order, and contains a planktic foraminiferal and calcareous nannofossil record of Pliocene events of the mid-latitude northwestern Pacific. The geological age of these units is based on magneto- and biostratigraphy. Five calcareous nannofossil datum horizons are recognized: the last occurrence (LO) of Reticulofenestra pseudoumbilicus, the termination of acme zone II of Reticulofenestra minutula var. C, the LO of R. minutula var. B, calcareous nannofossil datum plane A, and the termination of acme zone I of R. minutula var. C. Six planktic foraminiferal bioevents are also recognized: a coiling direction change, from sinistral to dextral, in the genus Pulleniatina; the first occurrence (FO) of Globorotalia crassaformis; the LOs of Globorotalia margaritae, Sphaeroidinel- lopsis seminulina, and Dentoglobigerina altispira; and the FO of Neogloboquadrina asanoi. The presence of two calcareous nannofossil bioevents, Datum A and the termination of acme zone I of R. minitula var. C, suggests that the normal and reversed polarity intervals of the upper part of the Takanabe Formation correspond to Chron C2An.1n (latest Gauss Normal Epoch) and Chron C2r.2r (earliest Matuyama Reversed Epoch), respectively. Based on combined floral and faunal data and magnetostratigraphic chron boundaries from the ATNTS2004, the upper part of the Miyazaki Group is Middle to Late Pliocene in age.


Nishitsuji Y.,Technical University of Delft | Nishitsuji Y.,Mitsui Oil Exploration Co. | Doi I.,Kyoto University | Draganov D.,Technical University of Delft
Geophysics | Year: 2014

We have developed a new imaging technique of subsurface heterogeneities that uses Sp-waves from natural earthquakes. This technique can be used as a first screening tool in frontier exploration areas before conventional active exploration. Analyzing Sp-waves from 28 earthquakes (Mj 2.0 to 4.2) recorded by two permanent seismic stations, we built an image of the distributions of velocity discontinuities in southeastern offshore Hokkaido, Japan, where intraplate earthquakes in the Pacific plate frequently occur. Our results indicated the presence of three horizontally continuous, distinct discontinuities corresponding to geologic boundaries estimated in a previous study.We also derived the frequency-dependent quality factor Q for P- and S-waves and use it as a method of characterizing physical properties of subsurface structure. The waveform traces with coherent Sp-phases in the southern part of the study area generally show a constant Qs/ratio, and the waveform traces with randomly distributed phases in the northern part show a large variation of the Qp/ ratio (including several high values). © 2014 Society of Exploration Geophysicists. All rights reserved.


Hossain M.A.,Hokkaido University | Suzuki N.,Hokkaido University | Matsumoto K.,Hokkaido University | Sakamoto R.,Mitsui Oil Exploration Co. | Takeda N.,JGI Inc. Meikei Building
Journal of Petroleum Geology | Year: 2014

Petroleum in the Surma basin, NE Bangladesh (part of the Bengal Basin) ranges from waxy crude oils to condensates. The origin and source rocks of these hydrocarbons were investigated based on the distributions of saturated and aromatic hydrocarbons in 20 oil samples from seven oil and gas fields. The relative compositions of pristane, phytane and adjacent n-alkanes suggest that the source rock was deposited in a non-marine setting. The abundance and similar distribution of biphenyls, cadalene and bicadinanes in most of the crude oils and condensates indicates a significant supply of higher-plant derived organic matter to the source rocks. Maturity levels of the crude oils and condensates from the Surma basin correspond to calculated vitrinite reflectance (Rc) values of 1.0-1.3%, indicating hydrocarbon expulsion from the source rock at a comparatively high maturity level. The Rc values of oils from the Titas field in the southern margin of the Surma basin are relatively low (0.8-1.0%). Some oils were severely biodegraded. The similar distribution of diamondoid hydrocarbons in both biodegraded and non-biodegraded oils indicated similar types of source rocks and similar maturity levels to those of oils from the Surma basin. The Oligocene Jenam Shale and/or underlying non-marine deposits located at greater depths may be potential source rocks. The diversity of the petroleum in the Surma basin was likely due to evaporative fractionation, resulting in residual waxy oils and lighter condensates which subsequently underwent tertiary migration and re-accumulation. Evaporative fractionation due to modification of the reservoir structure occurred during and after the Pliocene, when large-scale tectonic deformation occurred in and around the Bengal Basin. © 2014 Scientific Press Ltd.


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Mitsui Oil Exploration Co. | Date: 2011-08-30

Fuels. Excavating work of natural resources, such as oil and gas; drilling of wells; installation of oil pipelines for oil and natural gas. Transport of crude oil, gas and oil refined products by pipelines; transport of crude oil, gas by vessels; transport of crude oil, gas by railways; transport of crude oil, gas by vehicles; gas supplying; storage service of crude oil, gas and oil refined products by tank. Geological surveys or research; consultancy in the field of surveys or research of oil or natural gas; investigation, analysis, experiment or research of oil or natural gas; engineering of oil or natural gas plants.

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