Location:

Period:

23 Jan 2011 10:58:26 - 24 Jan 2011 00:59:09 (14 hours)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.4; Bonin Islands, Japan region; (21 Dec 2010) (33km from the swarm center)

7 swarms found nearby.

2010

PS20101221.1(45.5km)

21 Dec

1 day 21 hours

52 earthquakes

S20101222.3(12.0km)

21 Dec

4 days 11 hours

81 earthquakes

S20101222.1(45.5km)

21 Dec

4 days 10 hours

92 earthquakes

S20101222.2(81.4km)

21 Dec

4 days 22 hours

86 earthquakes

S20101222.4(21.6km)

21 Dec

2 days 11 hours

37 earthquakes

PS20101225.2(52.3km)

24 Dec

1 day 15 hours

8 earthquakes

2024

PS20241107.1(178.5km)

6 Nov

20 hours

7 earthquakes

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Seismic Swarm PS20110124.1 in the Bonin Islands Region

The Bonin Islands, also known as the Ogasawara Islands, lie within a tectonically active segment of the Izu-Bonin-Mariana volcanic arc in the western Pacific Ocean. This arc formed through the subduction of the Pacific Plate beneath the Philippine Sea Plate, producing a chain of volcanic islands, deep trenches, and frequent seismic activity. The region experiences both shallow crustal events and deeper intraslab earthquakes due to the complex geometry of the subducting slab, which dips steeply beneath the overriding plate.

SeismoSight internal records document swarm PS20110124.1 as a sequence of five earthquakes that began at 10:58 on 23 January 2011 and concluded at 00:59 on 24 January 2011. All events occurred within the Bonin Islands region and were recorded over a 14-hour period. The individual events registered magnitudes between 4.1 and 5.1 at focal depths ranging from 4 km to 15 km. The sequence included four events of magnitude 5.0 or greater, followed by a final magnitude 4.1 shock at the shallowest depth of 4 km.

This swarm represents one of six documented swarm episodes in the Bonin Islands region since 1 January 2000. The first such swarm occurred in 2010, indicating episodic clustered seismicity rather than isolated mainshock-aftershock sequences. The January 2011 activity took place shortly after a magnitude 7.4 earthquake on 21 December 2010, whose epicenter lay approximately 33 km from the swarm centroid. Such spatial and temporal proximity suggests possible stress transfer or fluid migration within the subduction interface and overlying crust.

Swarm events in subduction zones commonly arise from localized processes including fluid pressure changes, aseismic slip, or magma movement at depth. In the Bonin arc, shallow swarms such as PS20110124.1 may reflect fracturing within the forearc or volcanic basement, while the range of recorded depths points to activity spanning both the upper crust and the uppermost portion of the subducting slab. The tight temporal clustering without a dominant mainshock distinguishes the sequence from typical aftershock decay patterns.

Regional seismic monitoring has improved since 2000, allowing better characterization of these low-to-moderate magnitude clusters. Continued observation of swarm recurrence helps refine understanding of strain accumulation along the arc and potential links to larger megathrust events farther south in the Nankai or Ryukyu systems.

References

USGS Earthquake Catalog (Bonin Islands events 2000–2024)
Japan Meteorological Agency regional seismicity reports
Geological Survey of Japan, AIST: Izu-Bonin arc tectonics overview