Basement Structure by Airgun Reflection Survey in Osaka Bay, Southwest Japan

A number of civil engineering structures in a large area Kobe-Hanshin and Awaji in southwest Kinki, southwest Japan, were seriously damaged by the 1995 Hyogoken-Nambu earthquake. Geological studies were made to reveal both geological and geotechnical characteristics in and around the Osaka sedimentary basin. A geological map of the Osaka Plain and the surrounding area was compiled for the geotechnical engineering use.A Bouguer gravity anomaly map is presented with additional gravity measurements for an evaluation of the subsurface geologic structure. Data on the depth of the basement rocks was collected from information on deep drilling for the geologic survey or hot springs, reflection seismic exploration and surface geological survey. A configuration map of the basement rock forming the bottom of the Osaka basin was also compiled from the depth data collected and an analysis of the correlation between the depth and the Bouguer anomaly was attempted to outline the relief image.In order to assess the contribution of underground structure with faults to the distribution of structural damage, the focusing process of seismic wave was examined by using the ray theory applied to model the Uemachi Fault zone, which is located in a dense urban region in the Osaka area. As a result, the efficiency of the focusing based on a common underground structure with fault was substantiated qualitatively.

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“…Some buried active faults under the alluvial plain have been identified by seismic reflection technique in Osaka Bay (Iwasaki et al 1994) …”

Section: Geological Settingmentioning

confidence: 99%

Geological Characteristics and Problems in and Around Osaka Basin as a Basis for Assessment of Seismic Hazards

Nakagawa

Shiono

Inoue

et al. 1996

SOILS AND FOUNDATIONS

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“…As mentioned before, the alluvial fans extend on the south-east side of the Qaternary faults. The thickness of the sedimentary stratum under the alluvial fans suddenly increases toward Osaka Bay (Iwasaki et al, 1994). However, the second interpretation produces another question: why the damage on the reclaimed land or the lowland delta, which has very soft surface layers, is relatively light, compared with the damage on the alluvial fans.…”

Section: Discussionmentioning

confidence: 99%

Strong Motion Distribution in Kobe Area due to the 1995 Southern Hyogo Earthquake (M= 7.2) in Japan as Inferred from the Topple Rate of Tombstones.

Takemura

Tsuji

1995

J,Phys,Earth

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“…A fault that was named as the Osaka Bay Fault (Iwasaki et al, 1994), was found in the Osaka Bay, close to metropolises such as Osaka and Kobe (Fig. 2).…”

Section: Examples Of Active Fault Survey In the Sea 1) Survey Of Buri...mentioning

confidence: 99%

Proceedings of the First Joint Meeting of the U.S.-Japan Conference on Natural Resources (UJNR) Panel on Earthquake Research

Dietrich¹,

Nonomura²

1997

Open-File Report

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The Tokyo Metropolitan Area is situated above the triple-layered structure of the major tectonic plates: the North American, the Philippine Sea and the Pacific plates. The Communications Research Laboratory (CRL) had developed the Crustal Deformation Monitoring system for the Tokyo Metropolitan Area using both VLBI and SLR. This program is called the "KeyStone Project (KSP)" The four observation stations (Kashima, Koganei, Miura, and Tateyama) in this program are located around the Tokyo Metropolitan Area This system is characterized by no operator at each station, and by the remote operation system from the center station, and by real time VLBI system. The real time VLBI was realized this summer.The first 24 hours test experiment was conducted on 29th August in 1994, and we started 5 hours experiments between Kashima and Koganei on every week days since 31th of January in 1995 Since December in 1995. Miura sntion was participated and the daily 5 hours VLBI experiments have conducted on six baselines among Kashima. Koganei, Miura and Tateyama since September in 1996 Since the VLBI experiments were conducted in 64 Mbps mode as the test period, the observed precision was 6mm in the horizontal movements and 3cm for the vertical movements. The precision was three times worse than the final performance. The VLBI experiments in the 256Mbps mode will be started in this autumn The precision in VLBI will be 2mm for horizontal movement and baseline length, and 1cm for vertical movement in the regular 5 hours VLBI experiment, and the half of these precision will be obtained for 24 hours VLBI experiment. SLR observations will be conducted always in the clear sky The precision in SLR are expected to be a few mm The SLR observation will be started at early next year.Koganei station is moving in rate of 5mm/year towards North-East direction, and Miura station is moving in the rate of 25 mm/year towards North-West direction with respect to Kashima station The Miura station is moving down in the rate of 2cm/year. The movement of Kashima obtained in the global VLBI network was corrected, and the movements at Kashima, Koganei and Miura against the Norm American Plate were obtained. The direction of movement at Kashima agreed with the pressure of Pacific plate motion, the direction of movement at Koganei and Miura agreed with the motion of Philippine Sea plate.

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Basement Structure by Airgun Reflection Survey in Osaka Bay, Southwest Japan

Cited by 10 publications

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Geological Characteristics and Problems in and Around Osaka Basin as a Basis for Assessment of Seismic Hazards

Geological Characteristics and Problems in and Around Osaka Basin as a Basis for Assessment of Seismic Hazards

Strong Motion Distribution in Kobe Area due to the 1995 Southern Hyogo Earthquake (M= 7.2) in Japan as Inferred from the Topple Rate of Tombstones.

Proceedings of the First Joint Meeting of the U.S.-Japan Conference on Natural Resources (UJNR) Panel on Earthquake Research

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