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Information message about a strong earthquake in the Pacific Ocean, southeast of Loyalty Island, February 10, 2021.

An earthquake (catastrophic at the epicenter on the SHSI-17 scale) with M = 7.1 occurred on February 10, 2021 at 13:19 GMT (16:19 Moscow time) in the Pacific Ocean, SE of the Loyalty Islands.

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.

The map shows the epicenter of the earthquake with a red marker, its origin was in the Pacific Ocean, SE of the Loyalty Islands, New Caledonia, at a depth of 10 km, 396 km E-SE of the port of Tadine, Mare Island, New Caledonia, 633 km E-SE of Noumea , capital of New Caledonia and 647 km S-SE of Port Vila, capital of Vanuatu.

	Time in origin (GMT)	Latitude, degree	Longitude, degree	Depth, km	Stations number	Ms/N	mb/N	I0 (calculated)	GAP	Center
1	13:19:57.0	-22.75	171.5	10.0	41	7.1/29	6.5/22	10-10.5	192	GS RAS(Verified) Federal research center, Geophysical survey of Russian Academy of Sciences
2	13:19:59.6	-23.25	171.49	10.0	323	Mw 7.7			18	CSEM European - Mediterranean seismological center
3	13:19:55.9	-23.05	171.6	10.0	194	Mw 7.7/54	6.5/99		22	NEIC National Earthquakes Information Center of US Geological Service

Fig. 1 presents fragments of records obtained from digital stations Monsavu (∆ 7.9º), Stephens Creek (∆ 28º), Tennant Creek (∆ 34.7º), Matsushiro (∆ 66.8º), Taejon (∆ 72.1º). Fig. 2 presents fragments of records obtained from digital stations Yuzhno-Sakhalinsk (∆ 74.1º), Petropavlovsk (∆ 76.5º), Kuldur (∆ 79.9º), Magadan (∆ 83.8º), Yakutsk (∆ 90.6º).

Image 1

Image 2

GS RAS registered 3 foreshocks with М> = 5.4 within an hour before the main shock and 31 aftershocks with М> = 4.9 during the day after it.

N	Time in origin (GMT)	Latitude, degree	Longitude, degree	Depth, km	Stations number	Ms/N	mb/N	I0 (calculated)	Region
20210554	10/02/2021 12:24:21.0.0	-22.76	171.72	10.0	36		5.7/18	7-7.5	Southeast of Loyalty Islands
20210555	10/02/2021 12:32:10.0.0	-22.69	171.62	10.0	34		5.4/17	6-6.5	Southeast of Loyalty Islands
20210557	10/02/2021 13:01:59.0.0	-22.87	171.72	10.0	32		5.6/16	6.5-7	Southeast of Loyalty Islands
20210560	10/02/2021 13:57:17.0.0	-22.63	171.55	10.0	19		5.0/16	5-5.5	Southeast of Loyalty Islands
20210559	10/02/2021 14:18:19.0.0	-22.74	171.87	10.0	34		5.6/16	6.5-7	Southeast of Loyalty Islands
20210564	10/02/2021 14:30:23.0.0	-22.95	172.12	10.0	17		5.1/12	5.5-6	Southeast of Loyalty Islands
20210565	10/02/2021 14:37:21.0.0	-22.67	171.54	10.0	27		5.2/18	5.5-6	Southeast of Loyalty Islands
20210566	10/02/2021 14:49:56.0.0	-22.81	170.83	10.0	18		5.0/11	5-5.5	Southeast of Loyalty Islands
20210567	10/02/2021 14:59:37.0.0	-22.64	171.99	10.0	14		4.9/9	5-5.5	Southeast of Loyalty Islands
20210561	10/02/2021 16:35:21.0.0	-22.74	171.2	10.0	49		6.0/22	7.5-8	Southeast of Loyalty Islands
20210562	10/02/2021 17:25:49.0.0	-22.79	171.8	10.0	28		5.6/18	6.5-7	Southeast of Loyalty Islands
20210563	10/02/2021 18:36:40.0.0	-22.79	171.22	10.0	38		5.8/20	7-7.5	Southeast of Loyalty Islands
20210569	10/02/2021 19:56:14.0.0	-22.88	171.31	10.0	28		5.2/13	5.5-6	Southeast of Loyalty Islands
20210570	10/02/2021 20:45:13.0.0	-22.91	171.22	10.0	27		5.3/15	6-6.5	Southeast of Loyalty Islands
20210571	10/02/2021 21:23:59.0.0	-23.34	171.51	10.0	53		6.3/26	8.5	Southeast of Loyalty Islands
20210572	10/02/2021 21:40:33.0.0	-23.36	171.81	10.0	26		5.6/18	6.5-7	Southeast of Loyalty Islands
20210573	10/02/2021 21:49:58.0.0	-23.44	171.63	10.0	19		5.4/13	6-6.5	Southeast of Loyalty Islands
20210574	10/02/2021 21:57:10.0.0	-22.93	171.24	10.0	33		5.2/15	5.5-6	Southeast of Loyalty Islands
20210576	10/02/2021 22:03:42.0.0	-23.15	172.57	10.0	25		5.3/13	6-6.5	Southeast of Loyalty Islands
20210577	10/02/2021 22:38:00.0.0	-22.79	171.26	10.0	18		5.1/11	5.5-6	Southeast of Loyalty Islands
20210578	10/02/2021 22:54:17.0.0	-23.27	171.62	10.0	34		5.4/15	6-6.5	Southeast of Loyalty Islands
20210580	10/02/2021 23:26:27.0.0	-22.96	171.79	10.0	19		5.2/12	5.5-6	Southeast of Loyalty Islands
20210579	10/02/2021 23:32:46.0.0	-22.69	171.82	10.0	23		5.3/13	6-6.5	Southeast of Loyalty Islands
20210581	10/02/2021 23:45:14.0.0	-23.28	171.78	10.0	39		5.9/14	7.5-8	Southeast of Loyalty Islands
20210582	11/02/2021 00:14:45.0.0	-23.37	171.85	10.0	50		6.0/26	7.5-8	Southeast of Loyalty Islands
20210583	11/02/2021 01:02:03.0.0	-23.35	171.81	10.0	34		5.4/12	6-6.5	Southeast of Loyalty Islands
20210584	11/02/2021 01:24:39.0.0	-22.68	171.66	10.0	36		5.4/18	6-6.5	Southeast of Loyalty Islands
20210586	11/02/2021 04:15:16.0.0	-22.88	171.0	10.0	39		5.7/18	7-7.5	Southeast of Loyalty Islands
20210588	11/02/2021 06:52:32.0.0	-22.98	171.57	10.0	36		5.8/14	7-7.5	Southeast of Loyalty Islands
20210589	11/02/2021 07:18:40.0.0	-23.14	172.08	10.0	41		5.5/21	6.5-7	Southeast of Loyalty Islands
20210590	11/02/2021 07:56:03.0.0	-23.39	172.15	10.0	26		5.3/13	6-6.5	Southeast of Loyalty Islands
20210591	11/02/2021 08:22:09.0.0	-22.86	171.24	10.0	36		5.9/15	7.5-8	Southeast of Loyalty Islands
20210592	11/02/2021 08:39:12.0.0	-23.31	171.73	10.0	41		5.7/23	7-7.5	Southeast of Loyalty Islands
20210593	11/02/2021 11:19:25.0.0	-23.15	172.25	10.0	37		5.6/18	6.5-7	Southeast of Loyalty Islands

According to the U.S. Tsunami Warning System, a tsunami threat has been declared for New Zealand, Australia and some other parts of the Pacific Ocean. Maximum tsunami wave height0.78 m was observed in Lenakel, Vanuatu and 0.75 m on Great Barrier Island, New Zealand.
Fig 2 was obtained from USGS NEIC, it presents USGS Community Internet Intensity Map made by 5 responses in 3 cities.

Image 1

Click here to view detailed macroseismic data (DyfitWeb service)

The focal mechanism solution of the origin was obtained in GS RAS with signs of initial arrivals of P waves at 45 stationsб including 31 stations which registered compression wavs (plus sign) and 14 stations which registered tensile waves (minus sign). These stations are located in the interval of epicentral distances of 7.9-99º and in azymuth sector Az=7-353º. The focal mechanism solution in stereographic projection at the lower hemesphere and it's elements are presented in the table. The table also presents focal mechanism solutions of the origin obtained in USGS NEIC with W-phase Moment Tensor (Mww) technique and in Lamont-Dohert Earth Observatory, Columbia University, USA (LDEO GCMT) obtained withу СМТ (Centroid moment tensor) technique. The earthquake occurred under the influence of a slight prevalence of compressive stresses oriented to the south (AZ=176-181º). One nodal plane NP1 strikes SW (STK=214º) according to GS RAS and W-SW (STK=246º) according to USGS NEIC and W (STK=279º) according to LDEO GCMT, another plane NP2 strikes E (STK=87-101º). NP1 plane lies flatter (DP=16-23º) if compared with NP2 (DP=67-84º). The type of motion along NP1 – left latteral slip accorfing to GS RAS and thrust according to USGS NEIC and LDEO GCMT, along NP2 – reverse fault. The seismic moment according to USGS NEIC Mo=4.364*10**20 N*m, Mww=7.7. According to LDEO GCMT Mo=4.01*10**20 N*m, Mw=7.7.

Axes of main strengths			Nodal planes		Center
T	P	N	NP1	NP2	Center
PI: 49 Azm: 27	PI: 37 Azm: 178	PI: 14 Azm: 279	Stk: 214 Dp: 16 Slip: 24	Stk: 101 Dp: 84 Slip: 104	GS RAS Federal research center, Geophysical survey of Russian Academy of Sciences
PI: 60 Azm: 12	PI: 29 Azm: 176	PI: 7 Azm: 270	Stk: 246 Dp: 17 Slip: 65	Stk: 92 Dp: 75 Slip: 97	NEIC National Earthquakes Information Center of US Geological Service
PI: 67 Azm: 348	PI: 22 Azm: 181	PI: 4 Azm: 89	Stk: 279 Dp: 23 Slip: 101	Stk: 87 Dp: 67 Slip: 85	GCMT Lamont-Doherty Earth Observatory Global CMT Columbia University, USA

According to USGS NEIC the February 10 earthquake was caused by a thrust fault at or near the boundary between the Australian and Pacific plates, in the immediate vicinity of the New Hebrides Trench. At this point, the Australian plate is moving E-NE relative to the Pacific plate at a speed of about 75 mm / year.
The Loyalty Islands area is very active in seismic terms, in the region within 250 km of the earthquake on February 10 over the previous century, there were 15 more earthquakes with a magnitude greater than 7. The largest previous event in this area was an earthquake with a magnitude of M = 7.5 May 16, 1995 . The last strong previous event in this area was the earthquake of December 5, 2018 with a magnitude of M = 7.3 at 230 km W-NW of the earthquake on February 10.