|Budget Amount *help
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1994: ¥1,800,000 (Direct Cost: ¥1,800,000)
The present tectonic stress field in the southern part of the Kanto district, including the Izu peninsula, has been thought to be significantly affected by the interactions between the oceanic and continental plates. The northern part of the Philippine Sea plate is subducting beneath the continental plate from the Sagami and Suruga-Nankai troughs, and is colliding with the continental plate at the northern root of the Izu peninsula between the Sagami and Suruga troughs. Taking the inhomogeneity of the crust and upper mantle structure into consideration, we constructed the 3-dimensional finite element mesh model, and performed numerical simulations of the present tectonic stress field. We assumed the present stress field to have been formed through the tectonic processes since the beginning of the 18th centuty, when two mega-intraplate earthquakes occurred, i.e., the 1703 Genroke and the 1707 Hoei earthquake. Concerning the plate interactions, we assumed (1) the steady state movement of the Philippine Sea plate relative to the continental plate, i.e., 4 cm/yr in the direction of N30ﾟW,and (2) different faultings from place to place across the interface between the Philippine Sea and continental plates. The tectonic processes included the faultings associated with the 1854 Ansei-Tokai and the 1923 Kanto earthquake, the steady state faultings across the plate interface deeper than 30 km, and the virtual faulting across the virtual plate interface to the northwest of the Izu peninsula. This tectonic model could explain approximately the observed stress field, which is characterized by the fan-shaped distribution of compressional principal stress axs and the coaxial circular distribution of extensional ones.