September 6, 2018
Earthquake Research Committee,
Headquarters for Earthquake Research Promotion
* On September 6 at 03:07 (JST), there was a magnitude (M) 6.7 (provisional) earthquake at a depth of approximately 35 km in the central and eastern Iburi regions, Hokkaido. The maximum seismic intensity 7 was observed in the Iburi region and damage was caused by this event. The focal mechanism showed a reverse fault type with a compression axis in an ENE-WSW direction. This event occurred within the crust.
* The seismic activity after the M6.7 event is confined in the surrounding area of about 30 km length in NS. The seismic activity is high: there occurred 2 earthquakes with maximum seismic intensity 4 or over till 6th at 18 o'clock. The largest until 6th at 18 o'clock was an M5.5 (preliminary) earthquake on 6th at about 03:20 (JST).
* Large accelerations were observed such as 1,505 gal (synthesis of 3 components) at KiK-net Oiwake station in Abira town.
* According to the GNSS observation, crustal deformation accompanying this event is reported: southward displacement of about 5 cm (provisional) at Monbetsu station in Hidaka town and south-eastward displacement of about 5 cm (provisional) at Atsuma station in Atsuma town.
* The area extending from the eastern Iburi region and Hidaka region to offshore Urakawa has a characteristic that there occur many crustal earthquakes which are deeper than the ordinary depth ones in land. The recent seismic activity occurs in the area with such a characteristic. Also in the west of the recent seismic activity, there exists the Ishikari-teichi-toen fault zone extending in an NS direction.
* In the area where strong shaking was felt, it is necessary to be prepared
for an earthquake with maximum seismic intensity 7, for a week or so from
the occurrence of the earthquake. Especially in a few days or so, an earthquake
of a large magnitude often occurs.
Note:GNSS is a general name of satellite positioning system such as GPS.