1987年岩手県中部沿岸地震における岩手県内の高密度震度分布と地質構造との関係

摘要

A questionnaire survey was carried out to estimate the detailed seismic intensities on the Iwate Chubu-engan Earthquake of magnitude 6.6 of January 9, 1987. 5032 questionnare sheets were delivered to the persons living in and around Morioka City, to investigate the relation between thedetailed seismic intensities at every 500m×500m mesh and the subsurface structure　based on theboring data. Other 5122 questionnare sheets were delivered to the persons living in another area of Iwate Prefecture. The relation of intensity attenuation with distance was deduced and the relation between the intensity deviation and general geological stucture was investigated. Obtained results areas follows: 1)In Morioka City and its suburban districts, the detailed seismic intensity considerablydepends on the subsurface structure at the site. For example, deviations from the average intensity are -0.1~-1.0 in the district at where base rock of granite and shalstein is exposed or covered by sediment with sand and gravel. Conversely, at place of the soft ground constituted by volcanicmudflow and loam, they are +0.1~+0.7 2)From a view point of general geological structure in the whole Iwate Prefecture, seismicintensities are 0.1~0.6 greater than those expected from empirical formula at the valley of the Kitakami river and Toono basin where Quaternary fluvial plain depositis widely distributed. On the contrary, seismic intensities are 0.1~0.4 less than the average at the west of the Kitakami river where Tertiary system and Quaternary volcanic rocks are distributed, and the whole Kitakami mountains where pre-Tertiary is distributed.