駿河湾地域の地震時地殻上下変動 (南部フォッサマグナ・フィリピン海プレ-ト北縁のネオテクトニクス)

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The coseismic vertical crustal movements in the Suruga Bay region, the Philippine Sea coast of central Japan, during three historical large earthquakes are briefly reviewed with special reference to the late Quaternary seismic crustal movement in the region. According to abundant historical documents, at the time of the 1854 Ansei-Tokai earthquake of magnitude around 8.4, many places on the west coast of Suruga Bay were remarkably uplifted, whereas the east coast was scarcely displaced or slightly subsided. The general pattern of that crustal deformation strongly suggests that the earthquake was basically due to a large-scale thrust faulting along a plane dipping westerly from the Suruga trough running north-south in the middle of the bay so far as the eastern part of its rupture zone is concerned. The pattern of the 1854 coseismic crustal deformation is generally in good harmony with the distribution of late Quaternary tectonic landforms, submarine topography and active faults in the Suruga Bay region, which implies that the 1854-type faulting has recurred many times during the late Quaternary due to the northwestward underthrusting of the Philippine Sea plate at the Suruga trough. There is no positive record of uplift nor subsidence concerning the coseismic crustal deformation in the Suruga Bay region at the time of the 1707 Hoei earthquake of magnitude around 8.4, which is considered on the basis of macroseismic and tsunami data, to have been basically an 1854-type faulting so far as the Suruga Bay region is concerned. At the time of the 1498 Meio earthquake of magnitude around 8.6, which is also considered on the basis of macroseismic and tsunami data, to have been basically an 1854-type faulting so far as the Suruga Bay region is concerned. a point on the west coast of Suruga Bay considerably subsided. This subsidence is interpreted as deformation of the hanging-wall side of the 1854-type reverse faulting. The difference among the coseismic vertical crustal movements on the west coast of Suruga Bay in 1854, 1707, and 1498 suggests that secondary reverse or normal faults on the hanging-wall side of the main thrust contribute much to the surface deformations and that these subsidiary faultings do not always accompany the plate boundary main ruptures. These features of coseismic crustal deformations in the Suruga Bay region should be taken into account in the morphotectonic investigation of the region.
日本第四紀学会の論文

駿河湾地域の地震時地殻上下変動 (南部フォッサマグナ・フィリピン海プレ-ト北縁のネオテクトニクス)

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