The 2018 Hokkaido Eastern Iburi Earthquake (3)

b. Focal mechanism
In Fig. 2-6 are shown the focal mechanisms of earthquakes of M4.0 or over which occurred in the period from October 1, 1997 to September 6, 2018. The numbers of earthquakes in the surrounding area except for the recent seismic activity is small; most of them have focal mechanisms with a compression axis almost in an E-W direction. In Fig. 2-7 are shown the focal mechanisms of earthquakes of M4.0 or over which occurred after September 6, 2018. These focal mechanisms have a compression axis almost in an E-W direction and in harmony with the previous activity.

c. Past seismic activity
For the seismic activity since January 1923, in the area around the recent event (Area c), there have sometimes been earthquakes of M5.0 or over. In the vicinity of the recent event, on July 1, 2017, there was an M5.1 earthquake which caused damage with a seriously injured person (Fire and Disaster Management Agency). Also at the place about 80 km apart in the southeast direction from the recent event, there was "the 1982 Urakawa Earthquake" which caused damage with 167 injured persons and so on (Materials for Comprehensive List of Destructive Earthquakes in Japan).

Japan Meteorological Agency
[Evaluation of the 2018 Hokkaido Eastern Iburi Earthquake (October 12, 2018)]