Abstract:
In-situ stresses were measured at four sites, Hashikami, Fudai, Tono (KGJ) and Kamaishi, in the Pacific Ocean side of Kitakami mountains, northeastern Honshu, Japan. These measurements reveal the followings: 1) The "tensile stress" is predominant in north-south or northeast-southwest direction. Here, "tensile stress" means stress smaller than the overburden pressure. 2) The magnitude of largest compressive stress is nearly equal to the overburden pressure for these sites. 3) The horizontal stress is consistent with the horizontal strain of the crust obtained from the long-term geodetic measurement of about 100 years. 4) The direction, theta (sub hmin) , of "tension" axis appears be parallel to the polarization direction of fast split S-waves propagating in the upper mantle. 5) The direction, theta (sub hmin) , is almost parallel to the displacement velocity vector in ITRF97 coordinate system obtained by GPS observation for four years. 6) If the direction of displacement velocity vector in ITRF coordinate system is taken as an approximate direction of absolute displacement vector, focal mechanism solutions appear to be explained by the dislocations on weak faults in the displacement field. 7) By the review of the in-situ stress data of the ODP Hole 794C in the Sea of Japan on the Amurian plate, it is found that the "tension" axis lies approximately parallel both to the spreading direction of the Sea of Japan and to the direction of the largest P-wave velocity of the upper mantle. 8) The displacement velocity vector of the Amurian plate is estimated to be almost parallel to the spreading direction of the Sea of Japan. Assuming that the present displacement direction is still parallel to the spreading direction, the articles 7) and 8) suggest that the traction by upper mantle flow drives the crust and produces the stresses in the crust beneath the Sea of Japan. The relationships among stress, displacement velocity and anisotropy of seismic wave velocity for the Kitakami mountains are similar to the relationship for the crust beneath the Sea of Japan. This suggests that the upper mantle drives the intra-plate crust as well as the crust beneath the sea.