.RING-SHAPED SEISMICITY STRUCTURES IN VICINITY OF TOKYO: POSSIBLE PREPARATION FOR GREAT EARTHQUAKE

Abstract

We have been studying some seismicity characteristics in the vicinity of Japanese capital, Tokyo. It was established that two pairs of ring-shaped seismicity structures at depths of 0–33 and 34–70 km have been formed here in 1976–2018. Ring-shaped structures, as in the other subduction zones form prior to large and great earthquakes. They are characterized by threshold magnitude values (Mt1 and Mt2 correspondingly) as well as big axes lengths (L and l). The first ring pair, located mainly to the south of Tokyo, intersects partly with the rupture zone of the Great Kanto earthquake of 1923 (Mw 7,9), and the second one is to the east of the city. Earlier we have found correlation dependences of parameters Mt1 and Mt2 on magnitudes Mw of the main events for the west of the Pacific. Using these dependences we estimated magnitudes of possible great earthquakes: Mw 7,9±0,1 and 8,1±0,1 for the two areas mentioned correspondingly. It is supposed that in the near years the great earthquake is most probable to the east of Tokyo, because a rate of seismo-tectonic deformation has increased sharply in the area of the ring structure during the last decade.