Relation between characteristics of seismic activity and neotectonics in Honshu, Japan

Abstract

The nature of the occurrence of earthquakes in and around the Honshu region of Japan has been studied from the viewpoint of the relation with its neotectonics. Honshu Island (Japan) consists of two large crustal blocks; one is Northeast Japan and the other is Southwest Japan. The junction of these two blocks is the northern part of the Fossa Magna, which crosses the central part of Honshu. Tectonic forces in the crust, by which shallow earthquakes occur in the Inner Zone of Southwest Japan, are considered to be transmitted from Northeast Japan through this junction. Due to the transmission of these tectonic forces, the earthquake activity in the Inner Zone of Southwest Japan shows some significant characteristics that are closely related to major events in Northeast Japan. In particular, occurrences of large earthquakes along the eastern edge of the Japan Sea provide clear evidence of this. In some regions in Southwest Japan, seismic activity increases after the occurrence of large earthquakes along the eastern edge of the Japan Sea. In the northern part of the Fossa Magna region the seismic activity increases over a period of a few years after a large event along the eastern edge of the Japan Sea. Such evidence of seismic activity indicates that force transmission exists from the east to the west crustal block of Honshu Island (Japan).