Abstract
An investigation into plate tectonics in central Japan is conducted to make it clear what sort of motion is prevailing beneath the junction of Izu-Bonin and North Honshu arcs. At the beginning, an upper mantle model, consistent not only with deep seismic zones but also with the geometric constraints to the deformation of plate beneath the arc-junction, is proposed.
Negative travel-time anomalies by about 1 second due to the CAN-NIKIN explosion were observed in the belt in Southwest Honshu, which was also explained quantitatively by this model.
Most of the deep shocks in an isolated area in central part of Honshu were found to be aligned in the NW-SE trend along a range of about 90km. Their focal mechanism solutions were also almost identical with the model and indicate that the slab is locally under down-dip extension and the average strike of slip-planes may be NW-SE.
These results may suggest the existence of an active fault near the bent edge of slab and that the slab in the southwestern side of the fault moves downwards with respect to the other side to separate the Pacific plate beneath central Japan into two, the Izu-Bonin and North Honshu slabs.
