Location:

Period:

29 Jun 2025 03:16:01 - 6 Jul 2025 13:01:41 (7 days 9 hours 45 minutes)

Volcanoes in 100km radius:

Spurr(13km), Hayes(38km), Redoubt(91km)

Earthquakes:

15 swarms found nearby.

2021

S20210614.1(10.8km)

14 Jun

2 hours

37 earthquakes

2022

VS20221203.1(13.8km)

2 Dec

1 day 16 hours

40 earthquakes

2024

VS20240220.1(16.8km)

19 Feb

1 day 7 hours

27 earthquakes

S20240303.1(19.6km)

2 Mar

4 days 4 hours

89 earthquakes

VS20240308.1(15.6km)

7 Mar

4 days 5 hours

48 earthquakes

VS20240426.1(11.3km)

25 Apr

3 days 17 hours

68 earthquakes

VS20240519.1(13.6km)

18 May

3 days 19 hours

80 earthquakes

VS20241008.1(13.2km)

7 Oct

4 days 19 hours

110 earthquakes

VS20241028.1(11.0km)

27 Oct

2 days 13 hours

56 earthquakes

VS20241102.1(12.8km)

1 Nov

3 days 22 hours

85 earthquakes

VS20241123.1(12.1km)

22 Nov

2 days 17 hours

49 earthquakes

VS20241130.1(23.1km)

30 Nov

53 days 4 hours

1155 earthquakes

2025

VS20250201.1(19.5km)

31 Jan

63 days 9 hours

1115 earthquakes

VS20250507.1(12.6km)

6 May

25 days 14 hours

387 earthquakes

VS20250717.1(2.1km)

16 Jul

9 days 3 hours

170 earthquakes

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Seismic Swarm S20250630.1 Near Tyonek, Alaska: Event Analysis and Regional Context

Seismic swarm S20250630.1 was recorded 77 km west-northwest of Tyonek, Alaska, beginning at 03:16 on 29 June 2025 and concluding at 13:01 on 6 July 2025. Over 177 hours and 45 minutes, the sequence produced 78 earthquakes. Magnitudes ranged from -0.6 to 2.4, with the majority below 1.0 and depths predominantly between 0 and 6 km. Notable events included a magnitude 2.2 quake at 19:03 on 29 June at 0 km depth, a magnitude 2.4 event at 07:42 on 3 July at 125 km depth, and additional magnitude 2.4, 2.1, and 2.0 shocks on 4 and 6 July.

The swarm exhibited typical characteristics of clustered microseismicity, with shallow events dominating the early and late phases. A single deep event at 125 km suggests possible linkage to deeper subduction processes. Activity showed intermittent peaks, such as multiple events on 29 June and 1–6 July, without a clear mainshock-aftershock pattern.

This swarm represents the second recorded in 2025 and contributes to the 14 total swarms documented in the region since 1 January 2000. Prior swarms occurred in 2021 (1), 2022 (1), and 2024 (10), indicating episodic clustering in recent years.

The Tyonek area lies within south-central Alaska’s Cook Inlet region, part of the tectonically active Pacific-North American plate boundary. Ongoing subduction of the Pacific Plate beneath the North American Plate generates frequent earthquakes across a range of depths. Shallow crustal events often relate to local faulting within the overriding plate, while deeper activity aligns with the Wadati-Benioff zone. Historical records show this zone has produced significant events, including the magnitude 9.2 Great Alaska Earthquake of 1964, whose rupture extended across the broader subduction interface. Modern monitoring confirms persistent low-level seismicity and occasional swarms driven by fluid migration or stress transfer along the margin.

References

Alaska Earthquake Center, University of Alaska Fairbanks
U.S. Geological Survey Earthquake Hazards Program
SeismoSight internal swarm classification records