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Information message about a strong earthquake on the island of Hokkaido, Japan September 5, 2018.

A strong earthquake with M = 7 occurred on September 5, 2018 at 18:07 GMT (21:07 Moscow time) on the island of Hokkaido, Japan .

Parameters of the earthquake have been determined in the Alert Service (AS) of Information Processing Center (IPC) of Geophysical Survey of RAS in Obninsk with station data obtained from digital and analog seismic stations of Russia, countries of CIS and from abroad. Alert message on this earthquake has been delivered in 10 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).

Preliminary processing has been done with data from 25 stations, accurate processing - with data from 62.

The red marker on the map is the epicenter of the earthquake, the origin was located on the island of Hokkaido, Japan, at a depth of 33 km, 22 km E-NE of Tomakomai, Japan, 56 km SE of Sapporo, Japan and 357 km W-SW of Yuzhno- Kurilsk, Russia.

	Time in origin (GMT)	Latitude, degree	Longitude, degree	Depth, km	Stations number	Ms/N	mb/N	I0 (calculated)	GAP	Center
1	18:07:57.1	42.71	141.84	33.0	62	7.0/23	6.5/38	8-8.5	80	GS RAS(Verified) Federal research center, Geophysical survey of Russian Academy of Sciences
2	18:08:05.7	42.91	141.99	100.0	25		5.6/18			GS RAS(Preliminary) Federal research center, Geophysical survey of Russian Academy of Sciences
3	18:08:00.4	42.71	142.06	30.0	630	Mw 6.6			31	CSEM European - Mediterranean seismological center
4	18:07:58.9	42.67	141.93	33.4	143	Mw 6.6	6.5		31	NEIC National Earthquakes Information Center of US Geological Service

Fig. 1 presents fragments of records obtained from digital stations Yuzhno-Kurilsk (∆ 3.2º), Yuzhno-Sakhalinsk (∆ 4.3º), Kurilsk (∆ 5º), Matsushiro (∆ 6.8º), Ussuriysk (∆ 7.3º). Fig. 2 presents fragments of records obtained from digital stations Mys Shultsa (∆ 7.9º), Posyet (∆ 8.1º), Kuldur (∆ 9.6º), Severo-Kurilsk (∆ 12.6º), Taejon (∆ 12.8º).

Image 1

Image 2

GS RAS registered 6 aftershocks with M> = 4.6 within 5 hours after the main shock.

N	Time in origin (GMT)	Latitude, degree	Longitude, degree	Depth, km	Stations number	Ms/N	mb/N	I0 (calculated)	Region
20183457	05/09/2018 18:20:09.0.0	42.65	141.84	33.0	41		5.2/18	4-4.5	Hokkaido, Japan region
20183458	05/09/2018 19:10:47.0.0	42.62	141.83	33.0	32		4.9/20	3-3.5	Hokkaido, Japan region
20183459	05/09/2018 20:20:45.0.0	42.56	141.88	33.0	23		4.6/11	2.5-3	Hokkaido, Japan region
20183460	05/09/2018 21:04:31.0.0	42.68	141.69	33.0	26		4.6/14	2.5-3	Hokkaido, Japan region
20183461	05/09/2018 21:11:26.0.0	42.66	141.93	33.0	60		5.5/33	4.5-5	Hokkaido, Japan region
20183462	05/09/2018 22:45:48.0.0	42.75	141.94	33.0	22		4.7/11	2.5-3	Hokkaido, Japan region

According to TASS after the earthquake 44 people were killed, more than 300 people were injured (Fig. 1). The earthquake caused landslides in mountainous areas, where many small settlements are located. There were interruptions in the operation of the main energy source, which feeds the cooling system of the pools with used nuclear fuel at the decomissioned nuclear power plant Tomari. Currently, the supply of electricity to the station is fully restored. No leakage of radiation has been detected, changes in the radiation background near other nuclear facilities in the region also were not registered. On the island there was a large-scale power outage. Nearly three million houses were left without light. The earthquake caused disruptions in railway and air traffic - the traffic was suspended on many undeground lines and railways, and the main airport of the region - Shin-Chitose - was closed. Fig. 2 was taken from USGS NEIC, it presents USGS Community Internet Intensity Map made by 75 responses in 25 cities.

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Click here to view detailed macroseismic data (DyfitWeb service)

Focal mechanism solution of the origin was calculated in FIC GS RAS with signs of initial arrivals of P waves at 97 stations, 52 of them registered the waves of compression (plus signs), 45 stations registered tensile waves (minus signs). These stations are located in the interval of epicentral distances of 1.6-93.5º and in azimuth sector Az=9-353º. Focal mechanism solution in stereographic projection on the lower hemisphere is presented in the table.The table also presents solutions obtained in USGS NEIC with W-phase Moment Tensor (Mww) technique. Solutions for different centers are close. The earthquake arose under the action of insignificantly prevailing compressive stresses oriented E-NE. One nodal plane NP1 strikes south (STK=167-189º), another plane NP2 strikes N-NW (STK=333-338º). NP1 plane lies more horizontally (DP=22-30º) in comparison with NP2 (DP=61-71º). The type of motion along NP1 – thrust, along NP2 – reverse fault. According to USGS NEIC – Mo= 1.016 *10**19 N*m, Mw=6.6.

Axes of main strengths			Nodal planes		Center
T	P	N	NP1	NP2	Center
PI: 62 Azm: 231	PI: 25 Azm: 77	PI: 11 Azm: 342	Stk: 189 Dp: 22 Slip: 119	Stk: 338 Dp: 71 Slip: 79	GS RAS Federal research center, Geophysical survey of Russian Academy of Sciences
PI: 73 Azm: 225	PI: 15 Azm: 68	PI: 6 Azm: 336	Stk: 167 Dp: 30 Slip: 102	Stk: 333 Dp: 61 Slip: 83	NEIC National Earthquakes Information Center of US Geological Service
PI: 64 Azm: 272	PI: 24 Azm: 68	PI: 9 Azm: 162	Stk: 139 Dp: 23 Slip: 65	Stk: 346 Dp: 70 Slip: 100	GCMT Lamont-Doherty Earth Observatory Global CMT Columbia University, USA