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Information message about the strong earthquake in the Pacific Ocean, on the east coast of Honshu Island, Japan, February 13, 2021.

An earthquake (strong at the epicenter on the SHSI-17 scale) with M = 7.0 occurred on February 13, 2021 at 14:07 GMT (17:07 Moscow time) in the Pacific Ocean, on the east coast of Honshu Island, 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 8 min after registration to the Ministry of Emergency of the Russian Federation (EMERCOM).

Preliminary processing has been done with data from 10 stations, accurate processing - with data from 75.

The red marker on the map is the epicenter of the earthquake, its origin was in the Pacific Ocean, on the eastern coast of Honshu Island, Japan, at a depth of 10 km, 87 km E-SE of Sendai, 297 km N-NE of Tokyo, the capital of Japan, and 337 km S-SE of Aumori.

	Time in origin (GMT)	Latitude, degree	Longitude, degree	Depth, km	Stations number	Ms/N	mb/N	I0 (calculated)	GAP	Center
1	14:07:50.0	37.86	141.74	50.0	75	7.0/25	7.1/39	7.5	98	GS RAS(Verified) Federal research center, Geophysical survey of Russian Academy of Sciences
2	14:07:42.1	37.43	141.68	10.0	10		6.9/7	9.5-10		GS RAS(Preliminary) Federal research center, Geophysical survey of Russian Academy of Sciences
3	14:07:50.7	37.75	141.72	50.6	159	Mw 7.1/74	6.9/99		25	NEIC National Earthquakes Information Center of US Geological Service
4	14:07:52.1	37.43	141.65	60.0	315	Mw 7.1			33	CSEM European - Mediterranean seismological center

Fig. 1 presents fragments of records obtained from digital stations Matsushiro (∆ 3.1º), Erimo (∆ 4.3º), Yuzhno-Kurilsk (∆ 6.9º), Kurilsk (∆ 8.7º), Yuzhno-Sakhalinsk (∆ 9.1º). Fig. 2 presents fragments of records obtained from digital stations Kuldur (∆ 13.5º), Severo-Kurilsk (∆ 16.4º), Petropavlovsk (∆ 18.6º), Magadan (∆ 22.5º), Yakutsk (∆ 25.3º).

Image 1

Image 2

GS RAS registered seven aftershocks with М> = 4.6 within 20 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
20210643	13/02/2021 14:36:43.0.0	37.59	141.7	50.0	24		5.0/9	3	Near east coast of Honshu, Japan
20210644	13/02/2021 14:51:41.0.0	37.65	141.81	50.0	50		5.5/28	4-4.5	Near east coast of Honshu, Japan
20210647	13/02/2021 16:32:59.0.0	37.58	141.8	50.0	28		4.6/17	2	Near east coast of Honshu, Japan
20210652	14/02/2021 05:11:21.0.0	37.63	141.97	50.0	23		4.7/11	2-2.5	Near east coast of Honshu, Japan
20210653	14/02/2021 07:31:49.0.0	37.55	141.55	50.0	58		5.4/31	3.5-4	Near east coast of Honshu, Japan
20210654	14/02/2021 07:59:21.0.0	37.61	141.82	50.0	24		4.6/13	2	Near east coast of Honshu, Japan
20210658	14/02/2021 09:26:58.0.0	37.54	141.84	50.0	17		4.6/8	2	Near east coast of Honshu, Japan

According to TASS, 1 person died, more than 180 people were injured, 12 of them were seriously injured. In Japan, a tsunami threat was declared, but then this warning was canceled. Shinkansen high-speed trains have been suspended on several routes. One of the high-speed train lines connecting northeastern and northern Japan was damaged. A small amount of water splashed out of the spent nuclear fuel storage pools at reactors 5 and 6 of the Fukushima-1 nuclear power plant and the first reactor of the Fukushima-2 nuclear power plant. The earthquake led to an insignificant displacement of tanks with water cleared of radioactive particles at the Fukushima-1 nuclear power plant. In Tokyo, due to tremors that lasted more than a minute, equipment, furniture fell, and an emergency gas cut-off system was triggered. Strong tremors were felt in 10 prefectures in northern, northeastern and central Japan, including Fukushima, Miyagi and the metropolitan area.
Image 1 was obtained from USGS NEIC, it presnts USGS Community Internet Intensity Map made by 526 responces in 159 cities.

Image 1

Click here to view detailed macroseismic data (DyfitWeb service)

The focal mechanism solution of the origin of this earthquake was calculated in GS RAS with signs of initial arrivals of P waves at 94 stations, including 70 stations which registered compression waves (plus signs) and 24 stations which registered tensile waves (minus signs). These stations are located in the interval of epicentral distances of 3.1-96.6º and in azimuth sector Az=3-353º. The focal mechanism solution in stereographic projection on the lower hemisphere and its elements are presented in the table. The table also contains focal mechanism solutions obtained at the USGS NEIC with W-phase Moment Tensor (Mww) technique and in Lamont-Dohert Earth Observatory of Columbia University, USA (LDEO GCMT) with СМТ (Centroid moment tensor) technique. Solutions from different centers are close. The earthquake occurred under the action of significant prevalence of compressive stresses oriented W-NW (AZ=288-298º). One nodal plane NP1 strikes S-SW (STK=192-204º) according to GS RAS and LDEO GCMT and S (STK=187º) according to USGS NEIC, another plane NP2 strikes N-NE (STK=28-34º). NP2 plan lies more flat (DP=32-43º) if compared with NP1 (DP=49-58º). The type of motion along both planes – reverse faults. Seismic moment of this earthquake was obtained in the GS RAS from P-wave spectrum registered at the station "Obninsk" (∆67.6º), it makes Mo=4.6*10**19 N*m, Mw=7.1. Seismic moment according to USGS NEIC makes Mo=4.831*10**19 N*m, Mww=7.1. According to LDEO GCMT it makes Mo=5.80*10**20 N*m, Mw=7.1.

Axes of main strengths			Nodal planes		Center
T	P	N	NP1	NP2	Center
PI: 97 Azm: 76	PI: 13 Azm: 298	PI: 5 Azm: 207	Stk: 204 Dp: 58 Slip: 84	Stk: 34 Dp: 32 Slip: 99	GS RAS Federal research center, Geophysical survey of Russian Academy of Sciences
PI: 78 Azm: 33	PI: 3 Azm: 288	PI: 12 Azm: 197	Stk: 187 Dp: 49 Slip: 74	Stk: 30 Dp: 43 Slip: 107	NEIC National Earthquakes Information Center of US Geological Service
PI: 79 Azm: 63	PI: 8 Azm: 288	PI: 8 Azm: 197	Stk: 192 Dp: 53 Slip: 80	Stk: 28 Dp: 38 Slip: 103	GCMT Lamont-Doherty Earth Observatory Global CMT Columbia University, USA

According to USGS NEIC the earthquake on February 13 occurred as a result of a reverse fault movement near the interface area between the subduction zones between the Pacific and North American plates. At the site of this earthquake, the Pacific Plate is moving approximately westward relative to the North American Plate at a speed of 70 mm / year. The earthquake occurred 97 km W-SW of the Great East Japan Tohoku Earthquake of March 11, 2011 which occurred off the east coast of Honshu Island with a magnitude M = 8.8. That earthquake was followed by the tsunami and killed more than 15 thousand people, more than 6 thousand were seriously injured. Thousands of buildings were destroyed. The height of the tsunami waves exceeded ten meters. The Fukushima-1 NPP was in an emergency state due to the failure of the cooling system and it was a strongly contaminated with radioactivity.