February 12, 2019
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On January 3 at 18:10 (JST), there was a magnitude (M) 5.1 earthquake at a depth of approximately 10 km in the Kumamoto region, Kumamoto prefecture. The maximum seismic intensity 6 Lower was observed in the vicinity of the source in the Kumamoto region. The seismic activity after the event, confined in the area of about 5 km length extending in an NW-SE direction, is decaying but still continues. The largest earthquake until February 11 was an M4.3 earthquake occurring on January 26 with maximum seismic intensity 5 Lower.
* The focal mechanisms of earthquakes on January 3 and January 26 both had a tension axis in an N-S direction. These events occurred within the crust. The seismic source fault of the January 3 earthquake estimated from the focal mechanism and the distribution of aftershocks is a left-lateral strike-slip fault extending in an NW-SE direction.
* According to the result of GNSS observation and images from interferometry analysis of synthetic aperture radar data by the Advanced Land Observing Satellite-2 "DAICHI-2," no clear crustal deformation accompanying this event is observed.
* The source area of the recent event is situated in the neighborhood of the Beppu-Shimabara rift zone extending in an E-W direction in the central Kyushu, where the tensional force operates in an N-S direction and shows a characteristic that there occur many earthquakes whose focal mechanisms are normal fault type and/or strike-slip fault type. The recent event occurs in the area with such a characteristic.
* The area of the recent seismic activity is about 20 km north of the serial activity area of the 2016 Kumamoto Earthquakes. Before and after the recent seismic activity, no special variation in the serial activity area of the 2016 Kumamoto Earthquakes is observed.
Note: GNSS is a general name of satellite positioning system such as GPS.