Syntheses of the regional stress fields of the Japanese islands

The principal stresses in northern Honshu and in central-southwest Japan ar e synthesized on the basis of the ridge push, slab pull and across-are vari ation of differential forces due to crust/plate structural variation. Assum ing a more compressive north-south horizontal stress in central Japan-north ern Honshu than that; of southwest Japan, the calculated principal stress p rofiles explain the observed stress fields in these areas: namely, a strike -slip fault type for southwest-central Japan and a reverse fault type for n orthern Honshu, both having east-west sigma(Hmax) Kyushu is characterized b y the gradient of horizontal stresses both in the east-west and north-south directions, which cannot be explained by simple plate interactions or by c rust/plate structural variation. Combined with other lines of evidence for existence of mantle upwelling in the East China Sea west of Kyushu, it is p roposed that the stress gradient is produced by the viscous drag exerted by the flow spread laterally from the upwelling plume. The eastward movement of Kyushu and southwest Japan relative to Eurasia revealed by the recent Gl obal. Positioning System measurements conducted by the Geographical Survey Institute of Japan would be partly explained by this basal drag.