Seismic Swarm VS20240310.1 Near Karluk, Alaska

On March 10, 2024, a seismic swarm designated VS20240310.1 was recorded 82 km north of Karluk, Alaska. The sequence began at 09:25 and concluded at 17:31 local time, encompassing 24 earthquakes over 8 hours and 5 minutes. Magnitudes ranged from -0.2 to 1.7, with focal depths predominantly between 0 and 7 km, indicating shallow crustal activity.

The swarm exhibited typical characteristics of clustered microseismicity, with events distributed across the morning and early afternoon. Early activity included events at 09:25:58 (M 1.1, 7 km), 09:28:27 (M 1.3, 6 km), and 09:32:07 (M 1.4, 1 km). Later peaks featured a M 1.7 event at 09:41:41 (7 km) and additional small events through 17:31:56 (M 0.0, 6 km). Depths remained consistently shallow, consistent with localized stress release in the upper crust.

Karluk lies within the Kodiak Island region of southern Alaska, part of the tectonically active Aleutian subduction zone. Here, the Pacific Plate converges with and subducts beneath the North American Plate at rates of approximately 6–7 cm per year along the Aleutian Trench. This megathrust setting generates frequent earthquakes, ranging from deep intraslab events to shallow crustal swarms driven by fluid migration or fault interactions.

The area's seismic history includes multiple swarms since 2000, with 12 documented episodes: one in 2002, one in 2016, two in 2019, four in 2020, two in 2022, and two in 2023. These recurrent swarms reflect ongoing strain accumulation and release along the plate boundary and associated crustal faults. The 1964 Great Alaska Earthquake (Mw 9.2), centered nearby, remains the largest recorded event in the region and underscores the potential for larger subduction-related quakes.

Such swarms provide valuable data for monitoring stress changes but rarely produce significant ground shaking given their low magnitudes. Continued observation supports improved understanding of subduction dynamics in this high-hazard zone.

References

• USGS Earthquake Catalog (earthquake.usgs.gov)
• Alaska Earthquake Center (aeic.alaska.edu)
• SeismoSight internal swarm classification data