Temporal Change of the Earth's Horizontal Strain in Northeastern Part of Izu Peninsula, Japan
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概要
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The second order triangulation stations that are located in the northeastern part of the Izu peninsula, Japan, were surveyed at four times in 1884, 1925/1926 1931, 1973 respectively, and the earth's horizontal strains are calculated from survey data for three epochs. Remarkable strain changes near the Oiso hills and the coastal line between Odawara and Atami are noticed in the figure in which maximum shear strains for the first epoch 1884-1925/1926 are shown. These strain changes that are associated with the 1923 Kanto earthquake can not be interpreted by the fault model of the earthquake given by ANDO (1974). The detected strain relief should be attributed to the reverse faulting off the Oiso hills and along the Nishi-sagami-bay fault. The strain relief associated with the 1930 Ito earthquake swarm and the Kita-izu earthquake are found in the strain figure for the second epoch 1925/1926-1931. An anomalous maximum strain accumulation amounting to 5 × 10<SUP>-5</SUP> is detected near Atami in the strain figure for the third epoch. 1931/1973. This strain accumulation near Atami seems to originate from subduction of the Philippine Sea plate along the Nishi-sagami-bay fault as suggested by Ishibashi (1977). The results of strain analysis from survey data during 1931-1933/1934 show that some of detected strain accumulation originated from the creep dislocation at depth along the extension of the Nishi-sagami-by fault. Theref ere, the detected strain anomalies are nott always of a seismic nature that gives elastic rebound relating the subduction of the Philippine Sea plate. Finally, tectonic significances of the subduction zone bounded by the Sagami-bay fault and the Nishi-sagami-bay fault are emphasized. This boundary is nothing but the northern boundary of the Philippine Sea plate that is drifting to the direction N25°W at the present time, and the elastic or anelastic reverse f aultings along this boundary governn the seismo-tectonics in the south Kanto district.
- 日本測地学会の論文
日本測地学会 | 論文
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