Location:

Period:

23 Jul 2025 07:13:10 - 26 Jul 2025 13:29:32 (3 days 6 hours 16 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.3; 2025 Sand Point, Alaska Earthquake; (16 Jul 2025) (9km from the swarm center)

9 swarms found nearby.

2007

PS20071002.1(73.1km)

2 Oct

2 hours

5 earthquakes

2020

PS20200722.1(111.0km)

22 Jul

15 hours

6 earthquakes

PS20201019.2(51.3km)

19 Oct

1 day 4 hours

12 earthquakes

2025

S20250716.3(28.2km)

16 Jul

30 days 21 hours

1640 earthquakes

S20250716.4(14.7km)

16 Jul

14 days 21 hours

502 earthquakes

S20250717.2(11.9km)

16 Jul

3 days 10 hours

107 earthquakes

S20250716.2(19.1km)

16 Jul

1 day 7 hours

103 earthquakes

S20250717.1(7.0km)

16 Jul

15 hours

59 earthquakes

S20250717.3(27.7km)

16 Jul

7 days 2 hours

211 earthquakes

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Seismic Swarm S20250724.1: Analysis of Activity South of Sand Point, Alaska

Seismic swarm S20250724.1 occurred 89 km south of Sand Point, Alaska, from 07:13 on 23 July 2025 to 13:29 on 26 July 2025. Over 78 hours and 16 minutes, the event sequence included 60 earthquakes with magnitudes ranging from 1.5 to 3.4 and focal depths between 5 km and 35 km. This swarm represents the sixth such sequence recorded in the region during 2025 alone.

The swarm initiated with low-magnitude events clustered around 13–25 km depth. Early activity featured magnitudes of 1.7–2.7, transitioning to slightly deeper and varied events by late 23 July. On 24 July, magnitudes increased modestly, including a 2.9 event at 35 km depth and a 2.8 at similar depth. Activity on 25 July remained moderate, culminating in a 3.0 event at 15 km. The sequence peaked on 26 July with events reaching 3.2, 3.4, and multiple 2.7–2.9 magnitudes, primarily at 15–35 km depths before concluding.

Swarm patterns show a typical progression of clustered, low-to-moderate energy release without a dominant mainshock. Depths indicate activity within the upper to mid-crust, consistent with regional tectonic settings. Historical records since 2000 document nine prior swarms in the area, with notable occurrences in 2007 (one swarm), 2020 (two swarms), and six in 2025. These sequences often precede or follow larger regional events.

The swarm 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 environment produces frequent seismicity, including megathrust earthquakes and volcanic activity along the Alaska Peninsula and Aleutian Islands. The 16 July 2025 M7.3 Sand Point earthquake, located 9 km from the swarm center, likely influenced stress conditions that contributed to the subsequent swarm.

Regional geology features complex fault systems and volcanic arcs resulting from prolonged subduction since the Mesozoic era. Updated monitoring confirms ongoing aftershock potential following the July 2025 mainshock, with swarms serving as indicators of fluid migration or stress redistribution in the crust.

References
SeismoSight internal swarm classification data (S20250724.1).
USGS Earthquake Catalog for regional tectonic context and M7.3 event parameters.