Seismic Swarm S20230528.1 Near Pāhala, Hawaii
Seismic swarm S20230528.1 was recorded southeast of Pāhala on Hawaii's Big Island. The sequence began at 13:22 on 27 May 2023 and concluded at 07:42 on 4 June 2023, spanning 186 hours and 20 minutes. During this period, 89 earthquakes were registered at a location 11 km southeast of Pāhala.
The events exhibited magnitudes between 1.4 and 3.2, with the largest shock measuring 3.2 at 03:42 on 28 May. Depths clustered predominantly between 28 km and 34 km, though a few shallower events reached 5 km and 11–12 km. Early activity on 27 May included multiple events near magnitude 2.0 at depths around 30–33 km. Peak frequency occurred on 28 May, featuring the sequence's strongest quake alongside repeated magnitude 1.8–2.7 shocks at similar depths. Activity gradually declined through 29–31 May before sporadic larger events on 2–3 June, including two magnitude 2.8 shocks at depths of 11 km and 37 km.
Pāhala lies within the Kaʻū district on the southern flank of Kīlauea volcano. The region experiences frequent seismicity driven by volcanic processes, including magma intrusion, flank movement along décollement faults, and associated tectonic stresses. Depths around 30 km align with the approximate base of the volcanic edifice and underlying oceanic crust, where magma reservoirs and fault zones interact. Hawaii's geology is shaped by hotspot volcanism, producing shield volcanoes with active rift zones that channel magma and trigger earthquake swarms.
Since 2000, 41 swarms have occurred in the area, with notable increases in frequency during 2018–2022. Annual counts include single swarms in 2000, 2004, 2006–2008, and 2011, rising to four in 2015, five in 2018, seven in 2020, and six in 2021. These patterns reflect ongoing volcanic and tectonic adjustments beneath the island's southern sector.
The 2023 swarm fits established regional behavior, with event depths and magnitudes consistent with prior activity linked to Kīlauea's south flank dynamics. No surface deformation or eruptive activity was associated with this sequence.
References
USGS Earthquake Catalog (earthquake.usgs.gov)
Hawaii Volcano Observatory reports on Kīlauea seismicity
SeismoSight internal swarm classification data