| 講演要旨(和文) | | 大船渡市における振動特性を把握するため,2003年5月26日に宮城県沖で発生した地震に対し,市内の 14の小学校と8の中学校の全生徒3387世帯を対象とし,太田方式の震度アンケート調査を実施した。個体差を低減するために,回答から得られた震度は250m区画ごとに平均化し震度分布図を作成した。その結果,得られた震度の最大値は6.4,最小値は4.1,平均値は5.1であった。堆積層が分布する市内中心部で震度が大きく,花崗岩などが分布する周辺部では小さいことがわかった。区域ごとの震度の差異の原因を調べるために震度の既知地点近傍で常時微動観測を実施し,卓越周波数,平均rms振幅などの振動特性を解析した。その結果,250mメッシュでの震度ではなく微動観測点150m以内近傍の震度と2から5Hzの周波数帯の振幅との相関が高いことが判明し,地震時の揺れが常時微動解析結果で表されることがわかった。 |
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| | 講演要旨(英文) | | To clarify the vibration characteristics at Ofunato City of Iwate Prefecture, the survey of seismic intensity was done using questionnaires for Off-Miyagi earthquake occurred at May 26, 2003. The questionnaire revised by Ohta et al.(1998) was used for calculating seismic intensity. 3,387 questionnaires were distributed for parents of students of 14 elementary schools and 8 junior high schools of Ofunato City. The seismic intensities estimated from questionnaires were averaged for 250m square meshes to clarify the distribution of seismic intensity. To avoid differences among individuals for questionnaire survey, the effective mesh where the number of the questionnaire was more than three was used for analysis. The number of the effective mesh was 212 for Ofunato City. The seismic intensities were ranging from 6.4 to 4.1, and the average was 5.1 at Ofunato City. As a result, it was revealed that the seismic intensity at central area of Ofunato City was large, and the one around the area was small. The results show that the vibration characteristics depend on subsurface geological structure for the strong motions of Off-Miyagi earthquake. To clarify vibration characteristics, we carry out microtremor observations at 43 points where seismic intensity were estimated, using a three-component seismometer. The correlation coefficient between the microtremor rms amplitude and the seismic intencity were examined. As a result, it was revealed that the seismic intensity was large at the site where microtremor rms amplitude was large at a frequency range of 2 to 5 Hz. |
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