February 22, 2019
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion

Evaluation of Earthquake in the Central and Eastern Iburi Regions, Hokkaido on February 21, 2019

* On February 21 at 21:22 (JST), there was a magnitude (M) 5.8 (provisional) earthquake at a depth of approximately 35 km in the central and eastern Iburi regions, Hokkaido. The maximum seismic intensity 6 Lower was observed in the Iburi region. This event is considered as one of the aftershocks of the 2018 Hokkaido Eastern Iburi Earthquake, which was an M6.7 earthquake with seismic intensity 7 observed, occurring on September 6, 2018.

* The focal mechanism had a compression axis in an E-W direction. This event occurred within the continental plate.

* The seismic activity after the 2018 Hokkaido Eastern Iburi Earthquake, confined in the area of about 30 km length in NS, still continues. The recent event is situated in the northern part of the aftershock area.

* According to the GNSS observation (provisional) and the images of the interferometry analysis of PALSAR data by the Advanced Land Observing Satellite-2 "DAICHI-2," any significant crustal deformation accompanying the recent event is not observed.

* The area extending from the eastern Iburi region and Hidaka region to offshore Urakawa has a characteristic that there occur many earthquakes which are deeper than the ordinary crustal earthquakes in land. The serial seismic activity of the 2018 Hokkaido Eastern Iburi Earthquake occurs in the area with such a characteristic. Also in the west of the recent seismic activity, there exists the surface trace of Ishikari-teichi-toen fault zone extending in an N-S direction.

* The serial seismic activity of the 2018 Hokkaido Eastern Iburi Earthquake is decaying as a whole but still continues. It is necessary to be prepared for an earthquake.

Note: GNSS is a general name of satellite positioning system such as GPS.

• Earthquake in the Central and Eastern Iburi Regions at 21:22 on February 21, 2019 (JST) – Distribution of Seismic Intensity –
• "The 2018 Hokkaido Eastern Iburi Earthquake" – Table of Number of Earthquakes for Maximum Seismic Intensity –
• Comparison of Numbers of Earthquakes Associated with Major Earthquakes in Land and on the Coast (M3.5 or over)
• The 2018 Hokkaido Eastern Iburi Earthquake – Details of Seismic Activity (as of February 21, 2019 at 24:00)) –
• Focal Mechanism Solution of Earthquake at 21:22 on February 21, 2019 (JST) – Initial Motion Solution –
• Earthquake (M5.8) at 21:22 on February 21, 2019 (JST) and the Distribution of Aftershocks of the 2018 Hokkaido Eastern Iburi Earthquake
• Observed Data Before and After the Earthquake in the Central and Eastern Iburi Regions (February 21, M5.8) (provisional)
• Earthquake in the Central and Eastern Iburi Regions (February 21, M5.8) – Result of Interferometry Analysis of SAR Data by "Daichi-2" –