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Note:This page contains AI-generated content for informational and entertainment purposes only. It may contain inaccuracies. Raw event data is from USGS and EMSC. All statistics, lists, and derived information are generated by this site. Full disclaimerFound an error?
Location:
31 km S of Morton, Washington
Period:
14 Feb 2011 18:35:25 - 18 Feb 2011 16:02:45 (3 days 21 hours 27 minutes)
Volcanoes in 100km radius:
St. Helens(9km), West Crater(45km), Indian Heaven(49km), Adams(55km), Rainier(71km)
Earthquakes:
85
11 swarms found nearby.
2000
5 Nov
2 days 9 hours
45 earthquakes
2004
22 Sep
24 days 15 hours
2267 earthquakes
23 Oct
258 days 6 hours
5484 earthquakes
2005
19 Jul
53 days 4 hours
548 earthquakes
2008
17 Jan
3 days 11 hours
63 earthquakes
2011
29 Jan
2 days 1 hours
31 earthquakes
2013
S20130824.1(13.1km)
23 Aug
2 days 21 hours
56 earthquakes
2018
1 Jan
23 hours
24 earthquakes
S20180103.1(10.7km)
3 Jan
2 days 12 hours
81 earthquakes
6 May
7 days 23 hours
91 earthquakes
2019
12 Mar
36 minutes
24 earthquakes
AI-generated article — for informational and entertainment purposes only. May contain inaccuracies. Full disclaimerFound an error?

Seismic Swarm S20110214.1: Analysis of Earthquake Activity Near Morton, Washington

Seismic swarm S20110214.1 was recorded 31 km south of Morton, Washington, beginning at 18:35 on 14 February 2011 and concluding at 16:02 on 18 February 2011. Over this 93-hour-and-27-minute period, 85 earthquakes were detected. The sequence featured a mainshock of magnitude 4.3 at 4 km depth, followed by numerous smaller events with magnitudes ranging from -0.8 to 2.7. Depths were predominantly shallow, between 0 and 5 km, with one event reaching 16 km.

The swarm exhibited typical characteristics of clustered seismicity, with the highest event density occurring in the first 24 hours. Subsequent activity declined steadily, marked by occasional magnitude-2+ aftershocks on 15 and 17 February. All events were recorded within a compact source volume, consistent with fluid migration or stress redistribution along local fault structures.

The Morton area lies within the southern Washington Cascades, part of the Cascade volcanic arc formed by subduction of the Juan de Fuca plate beneath the North American plate. This tectonic regime produces both volcanic and tectonic seismicity. The region experiences background earthquake rates influenced by the broader Cascadia subduction zone, with shallow crustal events common due to north-south compression and volcanic processes associated with nearby edifices such as Mount St. Helens.

Historical records since 2000 indicate six documented swarms in the immediate vicinity, occurring in 2000 (1 swarm), 2004 (2 swarms), 2005 (1 swarm), 2008 (1 swarm), and 2011 (the present event). These episodes underscore recurrent, short-lived seismic clusters rather than prolonged mainshock-aftershock sequences.

Such swarms in the Cascades are often linked to hydrothermal fluid movement or minor magmatic activity at depth, although no surface deformation or volcanic unrest was associated with S20110214.1. The shallow focal depths observed align with regional patterns of brittle failure in the upper crust.

References

USGS Earthquake Catalog (Pacific Northwest regional data)
Pacific Northwest Seismic Network (PNSN) historical swarm documentation
Cascadia Subduction Zone tectonic framework summaries (USGS)