Earthquake Swarm VS20170416.1: Seismic Activity Near Honaunau-Napoopoo, Hawaii

The Kona coast of Hawaii Island lies on the western flank of the active Mauna Loa and Kilauea volcanic systems. This region experiences frequent seismic activity driven by the Hawaiian hotspot, where magma movement through the crust generates both volcanic tremors and tectonic stresses. Earthquake swarms here typically reflect fluid migration or dike intrusions rather than large tectonic events, consistent with the island's ongoing shield-volcano evolution since the Pleistocene. Swarm VS20170416.1 began at 06:13 on 15 April 2017 and concluded at 03:07 on 17 April 2017, lasting 44 hours and 54 minutes. It produced 56 earthquakes centered 24 km east of Honaunau-Napoopoo. Magnitudes ranged from 0.4 to 2.8, with the majority below 1.0. Depths clustered between 3 km and 5 km, though several events occurred at shallower levels near 0–2 km and a few registered negative depths, likely reflecting local datum adjustments. The sequence opened with a magnitude-1.0 event at 7 km depth. Activity intensified midday on 15 April, including a magnitude-2.0 shock at 3 km. The strongest event, magnitude 2.8 at 3 km, occurred early on 16 April, followed closely by a magnitude-2.6 event at 6 km depth later that morning. A magnitude-2.1 earthquake registered at essentially surface level (0 km) on the afternoon of 16 April. Subsequent events remained small and shallow, tapering off by early 17 April. These characteristics align with prior swarms documented in the area since 2000, when eight such sequences have been recorded. Earlier episodes occurred in 2004 (four swarms), 2015 (two swarms), and 2016 (one swarm). The 2017 swarm fits the established pattern of short-duration, low-magnitude clusters linked to subsurface magmatic or hydrothermal processes beneath the Kona flank. Such swarms contribute to ongoing monitoring of volcanic unrest. Although no surface eruption followed this event, the data illustrate the persistent seismic signature of Hawaii’s active geology. Continued observation supports hazard assessment for the densely populated Kona coast and surrounding communities. References
SeismoSight internal swarm classification VS20170416.1
USGS Hawaiian Volcano Observatory regional seismic summaries