Stress, strain, and mountain building in central Japan

Abstract

The work described here has two key objectives: to investigate the geometric relationships between the principal directions of crustal stress and crustal strain rate in central Japan and to evaluate how crustal stresses are related to the rates of horizontal strain produced by different tectonic processes. Specifically, we consider the extent to which tectonic stress directions reflect transient deformation produced by interseismic subduction thrust locking. The axis of maximum horizontal compressive stress obtained from focal mechanism inversion agrees well with the axis of greatest contractional strain rate in central and southwest Japan only after the effects of interseismic strain accumulation on geodetic observations have been accounted for according to an elastic dislocation model of subduction thrust locking. The residual deformation, which is presumed to represent net upper plate deformation, is broadly confined to the area of pronounced topography in central Japan and is consistent with the deformation expected for horizontal motion of the Amurian plate with respect to northeastern Honshu. These observations suggest that part of the apparent discrepancy between crustal stress and strain rate directions reported by previous authors stems from a comparison of parameters representing processes occurring on different timescales. In this case, the strain rates associated with cyclic subduction zone locking are not reflected in the crustal stress field; conversely, longterm horizontal motion between northeast and southwest Japan exerts a stronger influence on the crustal stress field and neotectonic mountain-building processes in central Japan than do intermittent subduction zone earthquakes. Copyright 2006 by the American Geophysical Union.