Location:

Period:

11 Mar 2011 07:47:49 - 14 Mar 2011 23:23:11 (3 days 15 hours 35 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.4; 100 km ENE of Miyako, Japan; (20 Apr 2026) (31km from the swarm center)

15 swarms found nearby.

2011

PS20110311.6(174.7km)

11 Mar

2 days 8 hours

50 earthquakes

PS20110311.1(163.8km)

11 Mar

1 day 14 hours

28 earthquakes

PS20110311.8(146.6km)

11 Mar

9 hours

5 earthquakes

PS20110315.1(53.3km)

14 Mar

1 day 10 hours

6 earthquakes

PS20110319.2(95.1km)

18 Mar

1 day 17 hours

8 earthquakes

PS20110323.1(24.9km)

22 Mar

23 hours

6 earthquakes

PS20110413.1(16.8km)

13 Apr

8 hours

6 earthquakes

PS20110916.1(42.0km)

16 Sep

1 day 11 hours

10 earthquakes

2012

PS20120314.1(197.0km)

14 Mar

2 hours

6 earthquakes

PS20120520.1(27.6km)

19 May

1 day 3 hours

9 earthquakes

2015

PS20150611.1(26.0km)

10 Jun

20 hours

5 earthquakes

2016

PS20160820.1(104.7km)

20 Aug

1 day 7 hours

6 earthquakes

2025

PS20251108.1(24.8km)

8 Nov

1 day 13 hours

25 earthquakes

PS20251208.1(166.7km)

8 Dec

18 hours

9 earthquakes

2026

PS20260420.1(33.7km)

20 Apr

21 hours

9 earthquakes

AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20110311.7 Off the Coast of Yamada, Japan

Seismic swarm PS20110311.7 occurred in the Pacific Ocean approximately 212 km east of Yamada, Japan, from 07:47 on 11 March 2011 to 23:23 on 14 March 2011. Over 87 hours and 35 minutes, the sequence produced 38 earthquakes with magnitudes ranging from 5.0 to 6.1 and focal depths between 13 km and 53 km.

This activity took place in the Japan Trench subduction zone, where the Pacific Plate descends beneath the Okhotsk Plate at a convergence rate of roughly 8–9 cm per year. The region is characterized by a well-developed accretionary prism and frequent megathrust and intraslab seismicity. The swarm began shortly after the Mw 9.0 Tohoku earthquake of 11 March 2011, consistent with widespread aftershock triggering along the plate interface and within the subducting slab.

The largest events reached magnitude 6.1 at 20:11 on 11 March (17 km depth) and magnitude 6.0 at 19:02 the same day (27 km depth). Shallower events (depths <20 km) clustered near the trench axis, while deeper events (30–50 km) occurred within the slab. Such depth variation reflects both interface thrust faulting and intraslab normal or strike-slip faulting typical of the post-megathrust stress regime.

Since 1 January 2000, only two swarms have been recorded in this sector, underscoring the relative rarity of clustered moderate-magnitude sequences outside major aftershock periods. The 2011 swarm represents the first of these episodes and illustrates how large subduction-zone earthquakes can induce prolonged, spatially confined seismic sequences through static and dynamic stress changes.

Geological studies of the Japan Trench confirm that the incoming Pacific Plate exhibits horst-and-graben structures that influence rupture segmentation. Post-2011 observations indicate accelerated slip and afterslip in the shallow megathrust, conditions that can promote swarm-like activity through fluid migration and stress redistribution.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Japan Meteorological Agency seismic database
International Seismological Centre event bulletins
Geological Survey of Japan, AIST – subduction-zone reports