Seismic Swarm S20231113.1: Analysis of Activity Southwest of Volcano, Hawaii

A notable seismic swarm, designated S20231113.1, occurred 10 km southwest of Volcano, Hawaii, on the Big Island. The sequence began at 10:16 on 12 November 2023 and concluded at 15:13 on 23 November 2023, spanning 268 hours and 57 minutes. During this period, 175 earthquakes were recorded. This activity aligns with the region's well-documented pattern of earthquake swarms linked to magmatic processes beneath Kīlauea volcano.

The swarm took place in a tectonically active zone influenced by the Hawaiian hotspot. Kīlauea, one of Earth's most active volcanoes, experiences frequent seismic swarms due to magma intrusion, dike propagation, and flank movement along the south flank. These events typically occur at shallow depths, reflecting brittle failure in the volcanic edifice and underlying crust. Historical monitoring by the U.S. Geological Survey confirms that such swarms have been recurrent since at least 2000, with 98 documented episodes through 2023. Annual counts show variability, including peaks of 14 swarms each in 2020 and 2023, alongside elevated activity in 2018 (9 swarms) and 2021 (8 swarms). Earlier years, such as 2003 (8 swarms) and 2004 (5 swarms), also indicate persistent unrest tied to the volcano's eruptive cycles.

Analysis of the first 100 events reveals predominantly low-magnitude earthquakes, with values ranging from 0.5 to 2.9. The majority clustered between 1.7 and 2.3, consistent with microseismicity driven by fluid migration or stress changes in the volcanic system. Depths were mostly shallow (0–3 km), suggesting activity within the upper volcanic layers, though later events in the sequence showed deeper foci up to 33 km, potentially indicating involvement of the deeper magmatic plumbing system. Temporal distribution showed initial high-frequency bursts on 12–13 November, followed by more dispersed occurrences through mid-November. Notable peaks included a 2.9 magnitude event at 1 km depth on 12 November and several 2.4–2.7 events at varied depths between 13 and 17 November. This pattern mirrors prior swarms associated with magma movement rather than large tectonic releases.

The geological setting features basaltic lava flows, rift zones, and fault systems that accommodate both eruptive and intrusive activity. Kīlauea's history includes continuous or near-continuous eruptions from 1983 to 2018, with renewed summit activity in 2021–2023. Seismic swarms often precede or accompany these phases by signaling pressure changes in the magma reservoir. The 2023 swarm's characteristics—high event count, limited magnitudes, and mixed shallow-to-intermediate depths—support classification as a typical volcanic swarm without evidence of imminent surface eruption based on the provided parameters.

Such sequences contribute to ongoing hazard assessment in the region, where communities near Volcano monitor for escalation. Continued surveillance remains essential given the area's dynamic nature.

References

• SeismoSight internal swarm classification data (S20231113.1 parameters and event list).
• USGS Hawaiian Volcano Observatory historical swarm statistics (2000–2023).