January 4, 2019
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On January 3 at 18:10 (JST), there was a magnitude (M) 5.1 (provisional) 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 is confined in the area of about 5 km length extending in an NW-SE direction. The largest earthquake until 4th at 14 o'clock (JST) was an M3.2 (provisional) earthquake occurring on 3rd at 18:48 (JST) with maximum seismic intensity 2.
* The focal mechanism showed a strike-slip fault type with a tension axis in an N-S direction. This event occurred within the crust. The seismic source fault 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 (provisional) of GNSS observation, no clear crustal deformation accompanying this event is reported.
* 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 stretches the northern Kyushu and the southern Kyushu 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.
* In the area where strong shaking was felt, it is necessary to be prepared for an earthquake with the seismic intensity of the same order, for a week or so from the occurrence of the earthquake. Earthquakes of large M often occur especially in a few days after the earthquake.