Earthquake Under the Northwestern Chiba Prefecture on October 7
On October 7, 2021 at 22:41 (JST), there was an M5.9 earthquake (maximum seismic intensity 5 Upper) at a depth of 75 km under the northwestern Chiba prefecture. The focal mechanism (CMT solution) showed a reverse fault type with a compression axis in an E-W direction. This event occurred at the boundary between the Pacific and the Philippine Sea plates.
This event caused damage with 32 injured persons and so on (as of October 8 at 06:30 (JST), Fire and Disaster Management Agency).
For the seismic activity since October 1997, in the vicinity of the recent event (Area b), there have sometimes been earthquakes of M5.0 or over. On July 23, 2005, there was an M6.0 earthquake (maximum seismic intensity 5 Upper) which caused damage with 38 injured persons, 12 partially collapsed houses, 47 confinements in elevator and so on.
For the seismic activity since January 1919, in the area around the recent event (Area c), the recent earthquake of M6.0 or over was the M6.0 one on July 23, 2005 and the former was the M6.0 one (maximum seismic intensity 4) on September 25, 1980. Note that in 1950s, there were 3 earthquakes of M6.0 or over observed and the seismic activity was rather high.
Japan Meteorological Agency
[Evaluation of Earthquake Under the Northwestern Chiba Prefecture on October 7, 2021 (October 8, 2021)]