Location:

Period:

21 Dec 2010 17:38:08 - 26 Dec 2010 04:53:46 (4 days 11 hours 15 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

4 swarms found nearby.

2010

PS20101221.1(33.8km)

21 Dec

1 day 21 hours

52 earthquakes

S20101222.4(24.4km)

21 Dec

2 days 11 hours

37 earthquakes

PS20101225.2(40.9km)

24 Dec

1 day 15 hours

8 earthquakes

2011

PS20110124.1(12.0km)

23 Jan

14 hours

5 earthquakes

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Seismic Swarm S20101222.3: Bonin Islands, Japan Region

A notable seismic swarm, designated S20101222.3, occurred in the Bonin Islands region of Japan between 17:38 UTC on 21 December 2010 and 04:53 UTC on 26 December 2010. Over 107 hours and 15 minutes, 81 earthquakes were recorded, with magnitudes ranging from 3.9 to 5.1 and focal depths predominantly near 10 km. This sequence represents the sole swarm documented in the region since 1 January 2000.

The events clustered tightly in both space and time, beginning with a series of magnitude 4.4–4.8 shocks on 21 December at depths of 4–17 km. Activity continued through 22–25 December, featuring repeated magnitude 4.3–4.9 events, and concluded with a final magnitude 4.3 shock on 26 December. Two events reached magnitude 5.1 on 25 December, marking the swarm’s peak. Depths remained shallow throughout, indicating activity within the upper crust rather than the deeper Wadati-Benioff zone typical of the area.

The Bonin Islands, also known as the Ogasawara Islands, form part of the Izu-Bonin-Mariana volcanic arc. This arc results from the subduction of the Pacific Plate beneath the Philippine Sea Plate at rates of approximately 4–5 cm per year. The tectonic setting produces both shallow crustal earthquakes and intermediate-to-deep events exceeding 300 km depth. The 2010 swarm aligns with known shallow seismicity patterns along the arc’s volcanic front, where magma movement or fluid migration can trigger clustered activity.

Historically, the Bonin region has experienced recurrent moderate seismicity. The arc’s volcanic islands, including Chichijima and Hahajima, overlie active submarine volcanoes that contribute to local stress changes. No larger mainshock–aftershock sequence accompanied the 2010 swarm, consistent with swarm behavior driven by aseismic processes rather than a single fault rupture.

SeismoSight internal classification identifies this sequence as an isolated swarm event without precedent in the post-2000 catalog for the immediate Bonin Islands area. Such swarms underscore the dynamic interplay between subduction-driven tectonics and local volcanic or hydrothermal systems.

References

USGS Earthquake Catalog (events 2010–2023)
Global Volcanism Program, Smithsonian Institution – Izu-Bonin arc summary
Geological Survey of Japan – Tectonic framework of the Philippine Sea Plate margin