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Location:
91 km E of Iwaki, Japan
Period:
22 Mar 2011 01:13:47 - 24 Mar 2011 07:03:55 (2 days 5 hours 50 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
14
M 7.0+:
M 7.9; 47 km E of ?arai, Japan; (11 Mar 2011) (46km from the swarm center)
20 swarms found nearby.
2005
PS20050119.1(181.5km)
19 Jan
10 hours
6 earthquakes
PS20050121.1(199.2km)
20 Jan
1 day 3 hours
8 earthquakes
2008
PS20080507.1(31.0km)
7 May
17 hours
11 earthquakes
PS20081220.1(99.1km)
20 Dec
22 hours
6 earthquakes
2011
PS20110311.2(62.4km)
11 Mar
21 hours
21 earthquakes
PS20110311.4(17.1km)
11 Mar
8 hours
57 earthquakes
PS20110311.5(34.4km)
11 Mar
7 hours
10 earthquakes
PS20110312.2(165.7km)
11 Mar
20 hours
6 earthquakes
PS20110312.1(189.1km)
11 Mar
1 day 3 hours
8 earthquakes
PS20110313.1(79.5km)
13 Mar
3 days 13 hours
14 earthquakes
PS20110314.1(99.2km)
13 Mar
13 hours
14 earthquakes
PS20110317.1(13.2km)
16 Mar
1 day 16 hours
10 earthquakes
PS20110319.1(126.0km)
18 Mar
1 day 7 hours
6 earthquakes
PS20110320.1(71.3km)
20 Mar
1 day 4 hours
6 earthquakes
PS20110322.3(106.4km)
22 Mar
12 hours
6 earthquakes
PS20110411.1(155.6km)
10 Apr
1 day 7 hours
7 earthquakes
2014
PS20140711.1(136.0km)
11 Jul
13 minutes
5 earthquakes
2016
PS20160923.1(148.0km)
22 Sep
18 hours
8 earthquakes
PS20161121.1(150.6km)
21 Nov
20 hours
11 earthquakes
2021
PS20210804.1(55.1km)
3 Aug
18 hours
5 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20110322.1: Eastern Offshore Japan

Seismic swarm PS20110322.1 occurred approximately 91 km east of Iwaki, Japan, in a tectonically active zone where the Pacific Plate subducts beneath the Eurasian Plate along the Japan Trench. This region forms part of the Pacific Ring of Fire and experiences frequent seismicity due to ongoing plate convergence at rates of 7–9 cm per year. The swarm was recorded between 01:13 UTC on 22 March 2011 and 07:03 UTC on 24 March 2011, lasting 53 hours and 50 minutes and comprising 14 events.

The sequence began eleven days after the magnitude 9.0 Tohoku earthquake of 11 March 2011. A magnitude 7.9 event located 47 km east of Ibaraki (46 km from the swarm centroid) on that date formed part of the early aftershock series and likely contributed to elevated stress in the surrounding crust. The subsequent swarm reflected continued readjustment along pre-existing faults in the overriding plate and within the subducting slab.

Event parameters are listed chronologically below:

  • 22 Mar 2011 01:13:47, magnitude 5.0, depth 42 km
  • 22 Mar 2011 05:59:38, magnitude 5.1, depth 49 km
  • 22 Mar 2011 09:19:06, magnitude 6.1, depth 31 km
  • 22 Mar 2011 12:04:08, magnitude 5.7, depth 45 km
  • 22 Mar 2011 12:48:57, magnitude 4.2, depth 35 km
  • 22 Mar 2011 13:50:51, magnitude 5.9, depth 20 km
  • 22 Mar 2011 15:03:46, magnitude 5.6, depth 19 km
  • 22 Mar 2011 16:05:51, magnitude 5.1, depth 45 km
  • 22 Mar 2011 16:12:09, magnitude 5.3, depth 31 km
  • 22 Mar 2011 23:46:53, magnitude 5.0, depth 35 km
  • 22 Mar 2011 23:46:59, magnitude 5.0, depth 70 km
  • 23 Mar 2011 20:43:13, magnitude 5.1, depth 21 km
  • 23 Mar 2011 20:43:27, magnitude 5.2, depth 75 km
  • 24 Mar 2011 07:03:55, magnitude 5.0, depth 38 km

Depths ranged from 19 km to 75 km, indicating activity both in the upper crust and within the subducting slab. The largest event reached magnitude 6.1 at 31 km depth on 22 March.

Since 1 January 2000, fourteen swarms have been identified in the same source region. Earlier episodes occurred in 2005 (two swarms) and 2008 (two swarms). Ten swarms, including the present sequence, took place in 2011, consistent with heightened aftershock productivity following the Tohoku mainshock.

The geological setting features a well-developed accretionary prism and forearc basin overlying the subduction interface. Historical records show that similar clusters of moderate-magnitude events commonly follow great earthquakes in this segment of the Japan Trench, reflecting viscoelastic relaxation and fluid migration along faults.

References
SeismoSight internal swarm catalogue PS20110322.1
USGS Earthquake Catalog (Tohoku aftershock sequence)
Japan Meteorological Agency regional seismicity reports