Location:

Period:

16 Jul 2025 20:43:11 - 20 Jul 2025 07:10:54 (3 days 10 hours 27 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

107

M 7.0+:

M 7.2; 2023 Sand Point, Alaska Earthquake; (16 Jul 2023) (14km from the swarm center)

7 swarms found nearby.

2007

PS20071002.1(62.1km)

2 Oct

2 hours

5 earthquakes

2020

PS20201019.2(58.6km)

19 Oct

1 day 4 hours

12 earthquakes

2023

S20230716.2(20.1km)

16 Jul

1 day 11 hours

30 earthquakes

2025

S20250716.4(12.8km)

16 Jul

14 days 21 hours

502 earthquakes

S20250716.2(30.0km)

16 Jul

1 day 7 hours

103 earthquakes

S20250717.1(17.0km)

16 Jul

15 hours

59 earthquakes

S20250724.1(11.9km)

23 Jul

3 days 6 hours

60 earthquakes

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Seismic Swarm S20250717.2: Analysis of Activity Near Sand Point, Alaska

Seismic swarm S20250717.2 was recorded 107 km south-southeast of Sand Point, Alaska, in the Shumagin Islands region of the Aleutian arc. The sequence began at 20:43 UTC on 16 July 2025 and concluded at 07:10 UTC on 20 July 2025, spanning 82 hours and 27 minutes. During this period, 107 earthquakes were detected.

Analysis of the first 100 events shows magnitudes ranging from 1.5 to 3.9, with the majority between 1.8 and 3.0. Depths varied from 1 km to 49 km, clustering predominantly between 10 km and 35 km. Early activity included several events above magnitude 3.0 within the first 24 hours, such as a 3.9 at 35 km depth and multiple 3.7s at similar depths. Later phases featured lower-magnitude events with shallower depths, indicating a gradual decrease in energy release while maintaining spatial coherence around the swarm center.

This swarm represents the fourth recorded since 2000, following sequences in 2007, 2020, and 2023. The 2023 swarm occurred in close temporal proximity to the magnitude 7.2 Sand Point earthquake on 16 July 2023, whose epicenter lay only 14 km from the current swarm location. Such recurrent swarms highlight persistent fault interactions within the subduction interface.

The Sand Point area lies within the Aleutian subduction zone, where the Pacific Plate converges with the North American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent seismicity, including both shallow crustal events and deeper intraslab activity. The Shumagin Islands segment has long been recognized for its potential to host moderate-to-large earthquakes, influenced by variable locking along the megathrust. Historical records document significant events in the broader Aleutian region, underscoring ongoing strain accumulation and release.

The 2025 swarm aligns with patterns of episodic seismic activity observed in subduction environments, where fluid migration or stress transfer from prior large events can trigger clustered earthquakes without a single dominant mainshock.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Alaska Earthquake Center (aeic.alaska.edu)
SeismoSight internal swarm classification S20250717.2