An earthquake swarm designated S20230130.1 was recorded 114 km east of McCarthy, Alaska. The sequence began at 18:22 on 29 January 2023 and concluded at 13:15 on 6 February 2023, spanning 186 hours and 53 minutes. During this period, 167 earthquakes were registered.
Analysis of the first 100 events reveals predominantly low-magnitude activity with shallow focal depths. The largest event reached magnitude 4.4 at a depth of 5 km on 30 January 2023 at 09:02:46. Other notable events include a magnitude 4.1 at 4 km depth on 3 February 2023 at 02:53:15 and a magnitude 3.2 at 5 km depth later that day. Magnitudes generally ranged between 0.8 and 2.9, with the majority below 2.0. Depths varied from surface level to 23 km, though most clustered between 3 km and 14 km, indicating shallow crustal processes.
The swarm exhibited typical characteristics of clustered seismicity, with events occurring in rapid succession during peak periods on 30 January and 3 February. No clear migration pattern is evident from the timing data, but the concentration of activity within a limited area suggests localized stress release.
The McCarthy region lies in the eastern Wrangell Mountains of south-central Alaska, within Wrangell-St. Elias National Park and Preserve. This area forms part of the tectonically active boundary between the Pacific and North American plates. Ongoing convergence, including the collision of the Yakutat terrane, drives crustal deformation, uplift, and frequent seismicity across the St. Elias orogen. The broader zone accommodates right-lateral strike-slip motion along major structures such as the Denali fault system and experiences both shallow crustal events and deeper subduction-related earthquakes.
Historical records indicate that seismic swarms are uncommon but documented in the vicinity. Since 1 January 2000, four prior swarms have occurred, with two in 2012 and two in 2013. These earlier sequences involved limited event counts relative to the 2023 activity.
The 2023 swarm contributes to ongoing monitoring of strain accumulation in this remote, glaciated terrain. Shallow events of this type may relate to glacial unloading or fluid migration within fractured bedrock, though detailed source mechanisms require further geophysical investigation. Continued seismic surveillance remains essential for assessing potential links to larger regional faults.