Location:

Period:

30 Oct 2012 02:49:02 - 30 Oct 2012 14:10:59 (11 hours 21 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

M 7.0+:

M 7.8; 206 km SW of Prince Rupert, Canada; (28 Oct 2012) (56km from the swarm center)

3 swarms found nearby.

2008

PS20080105.1(115.0km)

5 Jan

13 hours

6 earthquakes

2012

PS20121028.1(23.3km)

28 Oct

1 day 8 hours

23 earthquakes

2013

PS20130904.1(177.3km)

3 Sep

4 hours

5 earthquakes

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Seismic Swarm PS20121030.1: Insights into Regional Seismicity off British Columbia

A seismic swarm designated PS20121030.1 occurred 257 km SSW of Prince Rupert, Canada, on 30 October 2012. The sequence began at 02:49 UTC and concluded at 14:10 UTC, lasting 11 hours and 21 minutes. Five earthquakes were recorded during this interval, with magnitudes ranging from 5.0 to 6.2 and focal depths between 9 km and 23 km. This event took place in a tectonically active offshore region characterized by transform faulting along the Queen Charlotte Fault, which accommodates right-lateral motion between the Pacific and North American plates.

The swarm initiated with a magnitude 6.2 event at 02:49:02 UTC at a depth of 9 km. Two closely spaced events followed within minutes: a magnitude 5.3 at 02:55:08 UTC (19 km depth) and a magnitude 5.1 at 02:55:16 UTC (20 km depth). A magnitude 5.0 earthquake occurred at 04:40:15 UTC at 23 km depth, and the sequence ended with a magnitude 5.1 event at 14:10:59 UTC at 10 km depth. These events reflect clustered seismic energy release typical of swarms, where no single mainshock dominates and activity migrates spatially and temporally.

Geologically, the area forms part of the northern segment of the Cascadia margin transition into the Queen Charlotte Fault system. This transform boundary has produced significant historical earthquakes, including events exceeding magnitude 7. The swarm location lies near the aftershock zone of a magnitude 7.8 earthquake that struck 206 km southwest of Prince Rupert on 28 October 2012, approximately 56 km from the swarm centroid. Such proximity suggests possible triggering or stress redistribution following the larger rupture.

Historical records since 2000 indicate only two swarms in this region, one in 2008 and the present 2012 sequence. This low frequency underscores the episodic nature of swarm activity amid more continuous background seismicity driven by plate motion rates of roughly 5 cm per year.

The 2012 swarm provides a snapshot of how moderate-magnitude clusters contribute to strain accommodation along the fault without escalating to great earthquakes. Depths in the 9–23 km range align with the brittle-ductile transition zone expected in this oceanic-continental plate boundary setting.

References

Natural Resources Canada Earthquake Database
USGS Earthquake Catalog
Geological Survey of Canada tectonic summaries