Earthquake Swarm VS20041110.1: Seismic Activity Near Honaunau-Napoopoo, Hawaii

An earthquake swarm designated VS20041110.1 occurred in the region 27 km east of Honaunau-Napoopoo on the Big Island of Hawaii. The swarm began at 04:28 on 9 November 2004 and concluded at 08:09 on 3 December 2004, spanning 579 hours and 40 minutes. During this period, 334 earthquakes were recorded.

Hawaii’s geology is dominated by hotspot volcanism, where the Pacific Plate moves over a mantle plume, fueling the active volcanoes Kilauea and Mauna Loa. These volcanoes produce frequent seismic swarms as magma ascends through the crust, causing brittle failure in surrounding rock. The swarm location lies within the Kona district on the southwestern flank of the island, an area influenced by both volcanic and tectonic stresses associated with shield volcano growth and flank instability.

Historical records indicate 11 swarms in the region since 1 January 2000. These events clustered in specific years: two in 2000, five in 2003, and four in 2004. Such recurrent activity reflects ongoing magmatic and structural adjustments beneath the island’s volcanic edifices.

Analysis of the first 100 events reveals a predominance of low-magnitude earthquakes, with values ranging from 1.0 to 3.0. Depths were typically between 35 km and 48 km, consistent with mid-crustal processes beneath the volcanic pile, although occasional shallower events occurred at depths as low as 5 km. Early activity on 9 November showed magnitudes between 1.4 and 2.7 at depths near 40–48 km. Subsequent events through 12 November maintained similar magnitude distributions while exhibiting minor depth variations, including isolated events at 21 km and 23 km. The pattern indicates sustained seismic energy release without a dominant mainshock, characteristic of swarm behavior driven by fluid migration or stress diffusion rather than a single fault rupture.

This swarm aligns with the broader seismic character of Hawaii, where swarms often precede or accompany volcanic unrest. Depths in the 30–50 km range suggest involvement of the lower crust or uppermost mantle, where magma accumulation can trigger distributed microseismicity. The absence of damaging events underscores the swarm’s primarily scientific rather than hazardous significance.

References

• United States Geological Survey, Hawaiian Volcano Observatory seismic catalogs
• SeismoSight internal swarm classification records