HR: 0800h
AN: G21C-0675    [Abstracts]
TI: Intraplate Strain Accumulation in Central Japan
AU: * Sone, H
EM: hsone@stanford.edu
AF: Department of Geophysics, Stanford Universtiy, 397 Panama Mall Mitchell Building 360, Stanford, CA 94305, United States
AU: Zoback, M D
EM: zoback@stanford.edu
AF: Department of Geophysics, Stanford Universtiy, 397 Panama Mall Mitchell Building 360, Stanford, CA 94305, United States
AB: Crustal deformation in central Japan is caused by the combination of the elastic strain accumulation associated with interseismic locking of subduction thrusts and the deformation due to intraplate tectonic activities. Townend and Zoback (2006, JGR) showed that intraplate stress directions in central Japan (which they obtained from focal mechanism inversions of crustal earthquakes) are essentially the same as the intraplate strain directions, determined by Mazzotti et al. (2001, EPSL) by subtracting a modeled elastic deformation field due to plate subduction from the observed geodetic deformation field. The agreement between the horizontal principal stress directions and the directions of geodetic principal strains indicates a causal relation between the intraplate stress and strain fields. In order to compare the rate of strain release associated with intraplate seismicity with the rate of intraplate strain determined by Mazzotti et al, we carried out a moment tensor summation using the same set of earthquake focal mechanism as Townend and Zoback. We find that the principal horizontal strain directions associated with the earthquakes agree with those determined by subtracting modeled elastic deformation from geodetic observations (as well as the stress orientations obtained from focal mechanism inversions). However, the strain rates determined from moment tensor summation are only about 1/3, on average, of the geodetic strain. We interpret this difference as the accumulation of intraplate strain in central Japan, which could be released by intraplate earthquakes eventually. By mapping the differences between the long-term geodetic strain and intraplate seismic strain, we attempt to express the relative seismic hazards in central Japan in terms of the relative rate of strain accumulation.
DE: 1242 Seismic cycle related deformations (6924, 7209, 7223, 7230)
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
SC: Geodesy [G]
MN: 2007 Fall Meeting