Seismic Swarm VS20200317.1: Earthquake Activity Southwest of Volcano, Hawaii

Seismic swarm VS20200317.1 was recorded southwest of Volcano, Hawaii, beginning at 07:07 on 16 March 2020 and concluding at 09:57 on 19 March 2020. Over this 74-hour, 50-minute period, 34 earthquakes were detected. The events occurred at a location 7 km southwest of Volcano, with magnitudes ranging from 0.4 to 3.1 and depths predominantly at or near the surface (0 to 2 km).

The swarm exhibited a typical pattern of clustered, low-to-moderate magnitude events concentrated in the initial hours, followed by sporadic activity over subsequent days. The largest event reached magnitude 3.1 at 07:16 on 16 March. Multiple events registered at very shallow or slightly negative depths, consistent with volcanic or shallow crustal processes in the region. Activity tapered significantly by 19 March, with the final recorded event at magnitude 1.9.

Geological Context of the Region

The area southwest of Volcano lies on the Big Island of Hawaii, within the dynamic volcanic system associated with Kilauea volcano. Hawaii's geology is shaped by the Hawaiian hotspot, where magma from the mantle rises through the Pacific Plate, fueling persistent volcanic activity. Kilauea ranks among the most active volcanoes globally, with frequent eruptions, lava flows, and associated seismicity driven by magma movement, dike intrusions, and flank instability.

Earthquake swarms in this setting often result from fluid migration or pressure changes within the volcanic edifice rather than tectonic plate boundaries. Depths near zero kilometers align with shallow processes above or within the volcanic structure. The 2018 eruption of Kilauea demonstrated how such swarms can precede or accompany significant volcanic unrest, though each swarm requires separate evaluation.

Historical Seismic Patterns

Records since 2000 indicate 57 swarms in the region. Annual counts show variability, with notable increases in 2003 (8 swarms), 2018 (9 swarms), and lower activity in intervening years such as 2001 and 2005 (1 swarm each). This distribution reflects the ongoing volcanic dynamism of Kilauea and surrounding areas, where repeated swarms are a normal expression of subsurface magma and gas movement.

Swarm VS20200317.1 fits within this established pattern of episodic seismic clusters. Its duration and event count remain modest compared to more intense historical episodes, underscoring the routine nature of such activity in Hawaii's volcanic landscape.

Implications and Monitoring

Analysis of timing and magnitude distribution reveals an initial intense phase on 16 March, with 20 events in the first day, followed by reduced frequency. Such patterns aid in distinguishing volcanic swarms from tectonic sequences. Continued monitoring by agencies such as the Hawaiian Volcano Observatory supports timely assessment of any escalation toward eruptive activity.

References:
USGS Hawaiian Volcano Observatory reports on Kilauea seismicity and geology.
Hawaii hotspot volcanism literature from the U.S. Geological Survey.
SeismoSight internal swarm classification data VS20200317.1.