沈みこむプレート上に起伏がある場合の応力と地表変形の簡単なモデル計算

抄録

I propose a simple model to evaluate the possible mechanical and topographical effects that might be caused when an oceanic plate is subducted beneath the continental plate. The model will focus on the effects caused by perturbations such as oceanic ridges, seamounts and plateaus on the oceanic plate. The model consists of the two-dimensional Newtonian viscous fluid over the rigid basement with all the oceanic elements moving with a constant velocity. Applying Fourier transform analysis to the basic solutions for harmonic basal undulations, the basal shear stress and topographic profile caused by subducting oceanic ridges, seamounts, or plateaus were calculated. Assuming reasonable values for such physical constants as viscosity (10²² poise), density (3g/cm³), thickness of overriding plate (20km), height of ridge or seamount (1km), and subducting velocity (10cm/yr), the resultant surface profile varies asymmetrically from the top of 316m down to -260m, and the shear stress from -570bar up to 1270bar. The results from these calculations allow us to make quantitative estimates of the geological consequences of the past ridge subduction beneath island arcs but also give possible explanation for some of the uneven seismic activities found around present subduction zones.