著者

豊蔵 勇 岡田 篤正 牧野内 猛 堀川 義夫 長谷川 淳

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.108, no.5, pp.589-615, 1999-10-25 (Released:2009-11-12)

参考文献数

31

被引用文献数

1 2

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Construction of the Chubu International Airport has started off Tokoname City (Chita Peninsula) in Ise Bay. Various surveys such as bathymetry, seafloor drilling, sonic prospecting, and geologic examinations of recovered borehole core samples, have been performed to reveal soil engineering characteristics, submarine topography, and submarine geology at the airport site (Chubu Kuukou Chousakai=The Chubu International Airport Research Foundation, 1994). Many fruitful results on the submarine geology have been obtained in these surveys, as follows : (1) The submarine topography is divided into the inshore “Upper submarine terrace”, “Offshore gently sloping sea floor”, and “Submarine scarp” between the two. A submarine channel is trenched southwards on the inshore submarine terrace.(2) The bay area is underlain by the A, B, C1, C2, and T Formations, in descending order. The T Formation is Mio-Pliocene Tokoname Group, the basement of the bay area. The Tokoname Group forms a buried wave-cut platform of a peninsular shape, which extends southwards. On the east side of the peninsular wave-cut platform, a submarine buried valley stretches southwards under the submarine channel and is mostly filled with the A Formation. On the west side of the wave-cut platform runs the Ise Bay Fault, and the A, B, C1, and C2 Formations thicken offshore.(3) The A Formation, which is divided into the A1 (upper), A2 (middle), and A3 (lower) Members, consists of marine muddy strata of the present bottom surface and is correlated with the Nanyo Formation below the Nohbi Plain (north of the Ise Bay). The A Formation is 25 to 35 meters thick, and the 14C ages range from 9, 400 to 5, 200 y. B.P. of Holocene age.The A3 and A2 Member intercalates the U-Oki and K-Ah tephra, respectively, both are widespread tephra layers in Japan.(4) The B Formation, which is divided into the B1 (upper), B2 (middle), B3 (lower), and B4 (base) Members, consists of sand beds and gravelly beds. The B1, B2, and B3 Members are correlated with the Nohbi and First Gravel Formations below the Nohbi Plain, respectively. The B4 Member forms a buried terrace on the west slope of the peninsular wave-cut platform and is correlated with the Toriimatsu or Ohzone Formations, Lower Terrace Deposits in the eastern margin of the Nohbi Plain. The B Formation is of late Pleistocene age.(5) The C1 Formation consists mainly of marine clay beds about 40 meters thick. The fossil pollen composition indicates that the C1 Formation is correlated with the lower part of the Atsuta Formation in the Nohbi Plain and is of middle Pleistocene age.(6) The C2 Formation consists of sand (upper) and gravelly (lower) beds and exceeds 50 meters thick. The fossil pollen composition indicates that the C2 Formation is correlated with the Ama Formation below the Nohbi Plain and is of middle Pleistocene age.(7) The basement T Formation (Tokoname Group) consists of alternating sand and compact mud beds and intercalates two volcanic ash layers, which are correlated with the Souri (upper, Sr) and Higashitani (lower, Hg) Volcanic Ash Layers from the conformity in index of volcanic glass. The Souri and Higashitani V. A. Ls are intercalated within the upper horizon of the Tokoname Group in the Chita Peninsula.(8) The Ise Bay Fault (faults and flexure zone), trending in the NNW-SSE direction, extends in the western margin of the bay area. The Tokoname Group on the east side of the fault trends northwest and gently dips northeast. The Utsumi Fault, trending in the WNW-ESE dircction, extends in the southern margin of the peninsula.The geological relationship between the Chita Peninsula and airport site in the above-mentioned results brings the following problems for further study.

著者

豊蔵 勇 岡田 篤正

出版者

一般社団法人日本応用地質学会

雑誌

応用地質 (ISSN:02867737)

巻号頁・発行日

vol.37, no.2, pp.130-138, 1996-06-10

被引用文献数

3

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兵庫県南部地震と命名されたマグニチュード(以降Mと表す)7.2の都市直下型地震が、1995年1月17日未明の午前5時46分、阪神および淡路島地区を襲い、関東大震災以来の大震災をもたらした(表-1)。兵庫県南部地震は、淡路島北部に分布する野島断層およびその北東延長の活断層が再活動することによって発生したものである。このように、既存の活断層を震源とした直下型地震は、死者5,500名を上回る人的被害をもたらし、復興に要する費用は10兆円を越えると言われている。今回の地震が起きた時刻は、市民の生活がほとんど始まっていない早朝であった。このことは、もう少し遅い時刻で通勤電車、新幹線、高速道路をはじめとする大量輸送機能がフル稼働中であったならば、被害は別の形で大きくなっていた可能性が高く、社会に与えた影響は大きい。今回、活断層に関する解説を担当することとなった岡田は活断層の実態解明に長年携わった研究者として、また豊蔵は活断層調査を耐震設計のコンサルタント業務として携わってきた技術者として、まず活断層についてこれまで蓄積されてきた基本的な知識を整理し、活断層調査の持つ応用地質学的な意味や意義について述べ、さらに今後取り組むべき課題についても若干ふれる。

著者

豊蔵 勇 杉山 雄一 清水 惠助 中山 俊雄

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.116, no.3-4, pp.410-430, 2007-08-25 (Released:2009-11-12)

参考文献数

33

被引用文献数

1 1

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The Central Disaster Management Council presents several scenarios of hazardous earthquakes that might strike the Tokyo metropolitan area in the near future. After the Great Hanshin Earthquake (January 17, 1995, M7.3 on the JMA scale) which caused devastating damage to both human lives and economic activities, studies on major active faults throughout Japan were accelerated to evaluate their potential for producing serious earthquakes. Within the past decade, three inland earthquakes of M6.9 to 7.3 occurred in Japan without obvious surface ruptures. The faults that caused those earthquakes, had not been identified previously by active fault researchers.Since historic times, the Tokyo metropolitan area has been heavily inhabited and artificially modified by various constructions ; therefore its original geomorphologies, with which active faults are deciphered, have been almost lost to date. The authors summarized data on Quaternary faults found at three construction sites and twelve records of seismic profiles, and reexamined borehole data on restricted places in the metropolitan area. This revealed four concealed faults displacing middle to late Pleistocene deposits in Chuo Ward and one in Koto Ward. These concealed Quaternary faults are classified as Class C active faults with an average slip rate of 0.1 to 0.01m/1000 years. Active faults, however, have not been studied in the central metropolitan area for some reasons. The authors would like to call for an immediate full-scale active fault study to prepare for earthquake disasters in the heart of Tokyo.