著者

林 雅雄 稲盛 隆穂 佐伯 龍男 野口 聡

出版者

石油技術協会

雑誌

石油技術協会誌 (ISSN:03709868)

巻号頁・発行日

vol.75, no.1, pp.42-53, 2010 (Released:2012-03-01)

参考文献数

32

被引用文献数

11 13 1

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The Japanese Government has acquired regional reconnaissance seismic data in territorial waters since 1969 to evaluate the country's hydrocarbon potential. Total length of seismic lines is about 100,000 km and many surveys cover relatively deep water areas where gas hydrate stability zone (GHSZ) is expected to exist. BSRs related to methane hydrates in the offshore areas surrounding Japan were studied jointly by the group comprised of JNOC (at present, JOGMEC) and 10 private sectors based on these archived seismic data, and the areal extent of BSRs was reported to be 44,000 km2 in 2000.The country's research into methane hydrates has been accelerated since 2001 by establishment of the research consortium (MH21) under administrative guidance of METI. To investigate into methane hydrate, extensive 3D seismic surveys were conducted in the eastern Nankai Trough and many LWD wells were drilled there. Through the exploration campaign, certain new knowledge on seismic attributes related to the concentration of methane hydrates was obtained. In the light of this advanced knowledge about the appearance of BSRs, MH21 has decided that the archived seismic data should be investigated for the comprehensive understanding of methane hydrates as the potential future energy resources. Old seismic data processed suitably for loading in a “work station” was interpreted in the sophisticated system, though the volume of them was very limited.A method of high density velocity analysis was applied to the seismic data which recorded clear BSR appearing at abnormally shallow depth as 200msec below the sea floor in the Sea of Japan and in the Sea of Okhotsk, comparing to 500 to 700 msec in the Pacific side. This may represent that the geotectonic setting of the Japanese Islands controls GHSZ and this understanding seems to be important for the future exploration of MH.Present study has revealed that the areal extent of BSRs in offshore Japan is 122,000 km2.

著者

高野 修 西村 瑞恵 藤井 哲哉 佐伯 龍男

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.118, no.5, pp.776-792, 2009-10-25 (Released:2010-03-19)

参考文献数

28

被引用文献数

21 18

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Since previous research revealed that most of the methane hydrates in the eastern Nankai Trough area occur in matrix pores of turbidite sandstones, the facies distribution of turbidite sandstones may be one of the important keys to evaluate the distributions and actual volume of methane hydrates in the eastern Nankai Trough area. This paper attempts to reconstruct depositional processes of submarine-fan turbidites, and examines the relationship between turbidite facies distributions and bottom simulating reflector (BSR) occurrence as a proxy of methane hydrate using sedimentologic and sequence stratigraphic methodology. First, 2D/3D seismic survey data and well data including cores and logs were used to identify turbidite facies, seismic facies, and depositional sequences. The targeted Plio-Pleistocene Kakegawa and Ogasa Groups can be divided into 17 depositional sequences, and include six seismic facies indicating submarine-fan elements and surrounding slope to basin-floor environments. Next, facies maps for each depositional sequence unit were created by plotting all information on seismic facies, 3D seismic geomorphology, and well facies data. The obtained facies maps reveal that 11 major submarine canyons functioned as positionally fixed sediment supply systems from main land Japan, along which submarine fans were formed in the forearc basins. Submarine-fan depositional styles changed through Plio-Pleistocene from a braided channel type, through small radial fan, trough-fill fan, and muddy sheet fan types, to a channel-levee system type. Finally, the facies maps of each depositional sequence were overlaid with the BSR distribution. The overlaid maps indicate that the BSRs occur on feeder channels, distributary channels, and proximal lobes of submarine fans, suggesting that methane hydrates selectively occur in coarser grained portions of a submarine fan. Because the lower part of the Kakegawa Group is mainly composed of braided channel-type submarine fan turbidites, the lower Kakegawa horizon serves one of the major horizons bearing methane hydrates in the eastern Nankai Trough area.

著者

佐伯 龍男 梅田 康弘

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.41, no.2, pp.163-171, 1988-06-25 (Released:2010-03-11)

参考文献数

13

被引用文献数

2

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The high accelerations exceeding the earth's gravity were observed on the small area near the main shock of the 1984 Western Nagano Prefecture Earthquake (M=6.8). Few aftershocks occurred in this small high acceleration spot of main fault. It is inferred that great destruction producing the high accelerations occurred within this small spot. For detecting the evidence of great destruction, we tried to investigate the crack orientation and density by using Shear-wave polarization method.We have identified that directions of polarization in and out of the high acceleration spot are N40-70°W. These directions are consistent with the axis of maximum compression obtained from earthquake fault mechanisms and geodetic surveys. There are no difference in polarizations between in- and out of the high acceleration spot. It suggests that open-cracks had been made before the main shock. Great destructions of the main shock seems to have little influences on S-wave polarization. The average time-lag between arrival of leading and slower shear-wave is 0.02S. It indicates that present open-cracks are distributed in a shallow depth.

著者

梅田 康弘 黒磯 章夫 伊藤 潔 飯尾 能久 佐伯 龍男

出版者

公益社団法人 日本地震学会

雑誌

地震 第2輯 (ISSN:00371114)

巻号頁・発行日

vol.39, no.2, pp.217-228, 1986-06-25 (Released:2010-03-11)

参考文献数

27

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Many boulders were thrown off out of their former sockets by the Western Nagano Prefecture Earthquake of September 14, 1984. Anomalous high accelerations of 5-30g, in the frequency range of 5-10Hz, are estimated from the displacement of these thrown out boulders.Almost all of the thrown out boulders were found on the tops, ridges and suddles of the mountains covered with the volcanic ash. The amplification effects by topography and soil sediment of the surface are estimated from the observation of the aftershocks recorded on the mountain-top, -foot and rock. The spectral ratios of seismic waves with the frequencies of 5-10Hz, namely mountain-top/-foot and soil/rock, are 2-7 and 2-10, respectively.The accelerations on the basement rock are obtained dividing the accelerations estimated on the mountain-tops. The high accelerations exceeding 1g distribute within a small area with a length of 3km and a width of 1km. This small area corresponds to the large dislocation portion of the assumed fault and the low active region of aftershocks.