Recent seismic activity in the Tokai (Japan) region where a large earthquake is expected in the near future

Abstract

A large shallow earthquake is expected to occur in the Tokai region of central Honshu, Japan in the near future, and various intensive observations are being carried out in the region with the goal of predicting its occurrence. So far there have been no reports of any changes which could be regarded as precursors of the expected large earthquake in this area, but the following noteworthy changes have been observed in the seismic activity over the past decade. 1. (1)There has been a spate of large earthquakes of M 6.5–7 in a wide area surrounding the focal region of the expected Tokai earthquake. 2. (2) There has been a significant decline in seismic activity in the area along the Suruga Trough and the Nankai Trough, which includes the focal region of the anticipated earthquake. 3. (3) The hypocenters of earthquakes that have occurred in the Tokai district have migrated downward from shallow depths. Since these changes resemble the changes that have appeared before other large shallow earthquakes along the trench in the past, it is conceivable that they are long-term precursors of a large earthquake. Future changes in seismic activity in this area demand close attention.