Location:

Period:

16 Jul 2025 20:44:09 - 18 Jul 2025 04:14:53 (1 day 7 hours 30 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

103

13 swarms found nearby.

2007

PS20071002.1(86.8km)

2 Oct

2 hours

5 earthquakes

2011

S20110505.2(29.4km)

5 May

3 days 7 hours

50 earthquakes

2020

PS20200722.1(94.3km)

22 Jul

15 hours

6 earthquakes

S20200722.1(17.7km)

22 Jul

13 days 17 hours

332 earthquakes

PS20201019.2(53.8km)

19 Oct

1 day 4 hours

12 earthquakes

S20201020.2(25.0km)

19 Oct

5 days 0 hours

74 earthquakes

2025

S20250716.3(20.0km)

16 Jul

30 days 21 hours

1640 earthquakes

S20250716.4(24.9km)

16 Jul

14 days 21 hours

502 earthquakes

S20250717.2(30.0km)

16 Jul

3 days 10 hours

107 earthquakes

S20250717.1(13.0km)

16 Jul

15 hours

59 earthquakes

S20250717.3(25.4km)

16 Jul

7 days 2 hours

211 earthquakes

S20250724.1(19.1km)

23 Jul

3 days 6 hours

60 earthquakes

S20250728.1(25.4km)

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 S20250716.2 Near Sand Point, Alaska

A significant earthquake swarm designated S20250716.2 occurred approximately 105 km south-southeast of Sand Point, Alaska, in the Shumagin Islands region. The sequence began at 20:44 UTC on 16 July 2025 and concluded at 04:14 UTC on 18 July 2025, spanning 31 hours and 30 minutes. During this period, 103 earthquakes were recorded.

Analysis of the first 100 events reveals magnitudes ranging from 1.2 to 5.6, with the largest shock measuring 5.6 at a depth of 35 km on 17 July at 04:30 UTC. A second notable event reached magnitude 5.2 at 20 km depth shortly after the swarm onset. Depths predominantly clustered between 15 km and 38 km, with many events near 35 km, though shallower activity down to 6 km also occurred. Early phases featured several events above magnitude 4.0 within the first hours, followed by a gradual decline in both frequency and magnitude.

This activity aligns with the tectonic setting of the Aleutian subduction zone, where the Pacific Plate converges with and subducts beneath the North American Plate at rates of approximately 6–7 cm per year. The Shumagin Islands lie within a seismically active segment characterized by both megathrust and intraslab seismicity. Historical records indicate that earthquake swarms are recurrent in this area, often linked to fluid migration or stress transfer along the plate interface rather than a single mainshock-aftershock sequence.

Since 2000, nine swarms have been documented in the region, occurring in 2007 (one swarm), 2011 (one swarm), 2020 (four swarms), and 2025 (three swarms). These episodes typically involve hundreds of events over days to weeks and rarely produce damage given their moderate magnitudes and offshore locations. The current swarm’s characteristics, including its duration and magnitude distribution, are consistent with prior episodes in the same tectonic environment.

Monitoring by regional seismic networks continues to track after-activity, providing data that improves understanding of subduction zone processes and long-term seismic hazard assessment for nearby communities including Sand Point and surrounding Aleutian Islands.

References
USGS Earthquake Hazards Program – Alaska Seismicity
Alaska Earthquake Center – Regional Catalog and Swarm Reports
National Earthquake Information Center – Tectonic Summaries for the Aleutian Arc