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Location:
119 km SSE of Sand Point, Alaska
Period:
19 Oct 2020 20:54:38 - 21 Oct 2020 01:17:53 (1 day 4 hours 23 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
12
M 7.0+:
M 7.3; 2025 Sand Point, Alaska Earthquake; (16 Jul 2025) (59km from the swarm center)
M 7.2; 2023 Sand Point, Alaska Earthquake; (16 Jul 2023) (71km from the swarm center)
M 7.6; 2020 Sand Point, Alaska Earthquake; (19 Oct 2020) (33km from the swarm center)
27 swarms found nearby.
2007
PS20071002.1(118.0km)
2 Oct
2 hours
5 earthquakes
2011
S20110505.2(81.3km)
5 May
3 days 7 hours
50 earthquakes
S20110717.1(103.9km)
16 Jul
2 days 17 hours
34 earthquakes
2020
PS20200722.1(96.5km)
22 Jul
15 hours
6 earthquakes
S20200722.1(70.8km)
22 Jul
13 days 17 hours
332 earthquakes
S20200723.1(97.0km)
22 Jul
9 days 19 hours
135 earthquakes
S20200722.2(86.6km)
22 Jul
5 days 1 hours
126 earthquakes
S20200728.1(109.9km)
27 Jul
5 days 4 hours
111 earthquakes
S20200805.1(98.6km)
4 Aug
1 day 16 hours
45 earthquakes
S20200809.1(106.1km)
8 Aug
3 days 18 hours
43 earthquakes
S20201020.1(24.4km)
19 Oct
22 days 19 hours
647 earthquakes
S20201019.1(11.8km)
19 Oct
6 days 4 hours
164 earthquakes
S20201020.2(33.5km)
19 Oct
5 days 0 hours
74 earthquakes
S20201021.2(46.1km)
20 Oct
2 days 3 hours
40 earthquakes
S20201027.1(14.3km)
26 Oct
10 days 18 hours
233 earthquakes
S20201115.1(32.0km)
14 Nov
5 days 11 hours
97 earthquakes
S20201210.1(14.6km)
9 Dec
1 day 13 hours
36 earthquakes
2023
S20230716.2(74.0km)
16 Jul
1 day 11 hours
30 earthquakes
S20230716.3(97.8km)
16 Jul
6 days 3 hours
65 earthquakes
2025
S20250716.3(35.7km)
16 Jul
30 days 21 hours
1640 earthquakes
S20250716.4(66.0km)
16 Jul
14 days 21 hours
502 earthquakes
S20250717.2(58.6km)
16 Jul
3 days 10 hours
107 earthquakes
S20250716.2(53.8km)
16 Jul
1 day 7 hours
103 earthquakes
S20250717.1(54.3km)
16 Jul
15 hours
59 earthquakes
S20250717.3(28.6km)
16 Jul
7 days 2 hours
211 earthquakes
S20250724.1(51.3km)
23 Jul
3 days 6 hours
60 earthquakes
S20250728.1(36.7km)
27 Jul
2 days 4 hours
44 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20201019.2: Analysis of Activity Near Sand Point, Alaska

The seismic swarm PS20201019.2 occurred in the tectonically active region 119 km south-southeast of Sand Point, Alaska, within the Aleutian subduction zone. This setting arises from the convergence of the Pacific Plate and the North American Plate, where the Pacific Plate subducts northwestward at rates of 6–7 cm per year. The interaction generates frequent earthquakes, volcanic activity along the Aleutian arc, and associated seismic swarms due to stress transfer along the megathrust interface and crustal faults.

The swarm initiated at 20:54 UTC on 19 October 2020 with a magnitude 7.6 event at 28 km depth and concluded at 01:17 UTC on 21 October 2020. Over 28 hours and 23 minutes, 12 earthquakes were recorded. The sequence included a magnitude 5.7 event at 22 km depth shortly after the mainshock, followed by additional events ranging from magnitude 3.9 to 5.9 at depths between 12 km and 30 km. Notable shocks comprised magnitudes 5.7 (26 km), 5.0 (16 km), 5.2 (22 km), 5.5 (26 km), 5.1 (27 km), 5.9 (30 km), 5.6 (12 km), and two final magnitude 5.1 events at 22 km and 18 km.

This activity aligns with the broader historical pattern of the region. Since 1 January 2000, ten seismic swarms have been documented near Sand Point, with prior episodes in 2007 (one swarm) and 2011 (two swarms), followed by seven in 2020. The 2020 swarm occurred amid a period of elevated seismicity that also featured strong earthquakes, including a magnitude 7.6 event on 19 October 2020 located 33 km from the swarm center, a magnitude 7.2 event on 16 July 2023 at 71 km distance, and a magnitude 7.3 event on 16 July 2025 at 59 km distance.

Such swarms reflect episodic stress release in a subduction environment prone to both mainshock-aftershock sequences and clustered swarm behavior. Depths in the 12–30 km range indicate activity within the overriding plate and near the plate interface, consistent with the regional geology shaped by prolonged subduction since the Mesozoic era.

References

SeismoSight internal classification data for swarm PS20201019.2 and regional statistics.