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Location:
131 km E of Yamada, Japan
Period:
10 Jun 2015 08:33:03 - 11 Jun 2015 05:29:59 (20 hours 56 minutes)
Volcanoes in 100km radius:
None
Earthquakes:
5
M 7.0+:
M 7.4; 100 km ENE of Miyako, Japan; (20 Apr 2026) (50km from the swarm center)
15 swarms found nearby.
2011
PS20110311.6(163.6km)
11 Mar
2 days 8 hours
50 earthquakes
PS20110311.1(138.7km)
11 Mar
1 day 14 hours
28 earthquakes
PS20110311.7(26.0km)
11 Mar
3 days 15 hours
38 earthquakes
PS20110311.8(150.6km)
11 Mar
9 hours
5 earthquakes
PS20110315.1(55.5km)
14 Mar
1 day 10 hours
6 earthquakes
PS20110319.2(112.4km)
18 Mar
1 day 17 hours
8 earthquakes
PS20110323.1(46.3km)
22 Mar
23 hours
6 earthquakes
PS20110413.1(42.6km)
13 Apr
8 hours
6 earthquakes
PS20110916.1(60.3km)
16 Sep
1 day 11 hours
10 earthquakes
2012
PS20120314.1(188.5km)
14 Mar
2 hours
6 earthquakes
19 May
1 day 3 hours
9 earthquakes
2016
PS20160820.1(105.7km)
20 Aug
1 day 7 hours
6 earthquakes
2025
8 Nov
1 day 13 hours
25 earthquakes
PS20251208.1(184.4km)
8 Dec
18 hours
9 earthquakes
2026
PS20260420.1(19.6km)
20 Apr
21 hours
9 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm PS20150611.1 Off Yamada, Japan

Seismic swarm PS20150611.1 occurred approximately 131 km east of Yamada in Iwate Prefecture, Japan, within the tectonically active Japan Trench subduction zone. The event sequence began at 08:33 on 10 June 2015 and concluded at 05:29 on 11 June 2015, lasting 20 hours and 56 minutes. During this period, five earthquakes were recorded, with magnitudes ranging from 4.8 to 5.8 and focal depths between 5 km and 30 km.

The sequence initiated with a magnitude 5.8 event at 30 km depth on 10 June. The following day produced four additional shocks: two magnitude 5.7 events at 10 km and 5 km depths, a magnitude 5.4 event at 10 km, and a final magnitude 4.8 event at 10 km. All events clustered closely in time and space, consistent with swarm behavior where seismicity occurs without a dominant mainshock-aftershock pattern.

This region lies along the convergent boundary between the Pacific Plate and the overriding Okhotsk Plate. Subduction occurs at rates of approximately 8–9 cm per year, generating frequent earthquakes through megathrust slip, intraslab deformation, and crustal faulting. The offshore Sanriku coast has a well-documented history of seismic swarms linked to fluid migration and stress transfer within the subduction interface and overlying wedge.

Since 2000, eleven swarms have been identified in the area, including nine events in 2011 and two in 2012. These episodes reflect episodic strain release common in the forearc setting. The 2011 Tohoku-Oki earthquake (Mw 9.0) substantially altered regional stress fields, increasing swarm frequency in subsequent years through afterslip and viscoelastic relaxation.

Such swarms provide valuable data for understanding precursory processes and hazard assessment in subduction zones. Monitoring by regional networks continues to track microseismicity to refine models of plate coupling and potential large-event nucleation.

References

USGS Earthquake Catalog
Japan Meteorological Agency seismic reports
Geological Survey of Japan tectonic summaries