Seismic Swarm VS20230413.1: Analysis of Activity Southwest of Volcano, Hawaii

A seismic swarm designated VS20230413.1 was recorded 7 km southwest of Volcano, Hawaii, from 08:31 on 13 April 2023 to 23:17 on 15 April 2023. Over 62 hours and 45 minutes, 48 earthquakes were detected. This event cluster occurred in a region of persistent volcanic and tectonic activity associated with Kilauea volcano.

The swarm exhibited predominantly low-magnitude events. The largest reached magnitude 2.4, with most below magnitude 2.0. Depths ranged from the surface to 23 km, though the majority clustered between 0 and 8 km, consistent with shallow crustal processes. Activity peaked on 13 April with frequent small events, then declined gradually through 15 April. Notable events included a magnitude 2.3 at 08:31 on 13 April at 2 km depth, a magnitude 2.4 at 23:56 on the same day at 1 km depth, and several magnitude 1.9 events on subsequent days at depths of 1–4 km.

This swarm aligns with patterns observed in Hawaii’s dynamic volcanic environment. The Island of Hawaii sits above a mantle hotspot, driving the growth of shield volcanoes including Kilauea. The southwest location places the swarm near Kilauea’s Southwest Rift Zone and adjacent to the Hilina Fault System. These structures accommodate both magma intrusion and flank movement, generating earthquake swarms through dike propagation, pressure changes in the magmatic system, or slip along décollement surfaces.

Kilauea has produced frequent swarms throughout recorded history. Since 2000, 88 swarms have been documented in the area, with notable concentrations in 2020 (14 swarms), 2018 (9), 2021 (9), and 2022 (7). Earlier decades showed lower but consistent activity, such as 8 swarms in 2003 and 5 in 2004. These recurrent clusters reflect ongoing magma supply from depth and the volcano’s long-term eruptive behavior.

Seismic swarms at Kilauea often precede or accompany eruptive episodes, as seen during the prolonged 2018 lower East Rift Zone eruption and summit collapse. Shallow depths in the current swarm suggest involvement of the upper volcanic edifice rather than deeper mantle sources. The absence of larger events indicates limited stress accumulation, typical of fluid-driven swarms rather than tectonic mainshock-aftershock sequences.

Monitoring by the U.S. Geological Survey Hawaiian Volcano Observatory continues to track such activity for signs of renewed magma movement. The April 2023 swarm underscores the persistent seismic vitality of the region, where small-magnitude events serve as sensitive indicators of subsurface volcanic processes.

References:
U.S. Geological Survey Hawaiian Volcano Observatory reports on Kilauea seismicity and swarm statistics.
Internal SeismoSight classification data for swarm VS20230413.1 parameters and historical counts since 2000.