1995 Fiscal Year Final Research Report Summary
Studies on the Causes of Unique Strong Ground Motions Observed during the 1993 Hokkaido-Nansei-Oki Earthquake Sequence
| Project/Area Number |
06452409
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Natural disaster science
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| Research Institution | HOKKAIDO UNIVERSITY |
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Principal Investigator |
SASATANI Tsutomu Hokkaido University, Graduate School of Science, Associate Professor., 大学院理学研究科, 助教授 (10002148)
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| Co-Investigator(Kenkyū-buntansha) |
KUDO Kazuyoshi The University of Tokyo, Earthquake Research Institute, Associate Professor., 地震研究所, 助教授 (50012935)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Unique strong ground motion / The 1993 Hokkaido-Nansei-Oki earthquake / Site response / Unusually high peak acceleration / Soil-structure interaction / Liquefaction / Soft sedimentary basin / Basin-induced surface waves |
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| Research Abstract |
We carried out a temporal strong motion observation in the southwestern part of Hokkaido after the 1993 Hokkaido-Nansei-Oki earthquake (M7.8). Unusually high peak acceleration (-1.6g) was observed at OTB during the largest aftershock (8/8/1993 ; M6.3). The OTB station is located at the foot of a small cape (Shibino-Misaki) and its site response shows a sharp peak (a factor of about 80) at about 4 Hz. The unique site response was observed at KNK,located on a small, soft sedimentary basin in Kaminokuni, where liquefaction was observed during the main shock : the amplification factors are large (10to20) at low frequencies (-1 Hz), while they are less than l at high frequencies (>10 Hz). In order to clarify the causes of the above unique strong ground motions, we carried out the following geotechnical measurements near the observation sites : P-S logging, microtremore array observations, and geoelectrical soundings. The following results were obtained :
(1) The causes of the unique site response at OTB are combined effects of amplification due to shallow sediments overlaying very hard rock and soil-structure interaction.
(2) The causes of the unique site response at KNK are combined effects of amplification at low frequencies and deamplification at high frequencies due to very soft surface sediments. A part of the amplification at low frequencies is attributed to the basin-induced surface waves generated at the basin edge.
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[Publications] Kudo, K., T.Sasatani, M.Sakaue, S.Saito, H.Nagumo, and M.Takahashi: "Effects of surface soil and earthquake source radiation of the ground motion of 1.6g acceleration, observed during the August 8,1993, South-West Off Hokkaido earthquake, Japan" Proc. of the Ninth Japan Earthquake Engineering Symposium-1994, Tokyo. Vol.3. E-043-E-048 (1994)
Description
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