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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:
32 km S of Morton, Washington
Period:
29 Jan 2011 18:31:16 - 31 Jan 2011 20:05:28 (2 days 1 hour 34 minutes)
Volcanoes in 100km radius:
St. Helens(1km), West Crater(37km), Indian Heaven(41km), Adams(53km), Rainier(78km)
Earthquakes:
31
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
14 Feb
3 days 21 hours
85 earthquakes
2013
S20130824.1(17.3km)
23 Aug
2 days 21 hours
56 earthquakes
2018
1 Jan
23 hours
24 earthquakes
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 S20110130.1 Near Morton, Washington

A seismic swarm designated S20110130.1 occurred 32 km south of Morton, Washington, from 18:31 on 29 January 2011 to 20:05 on 31 January 2011. Over 49 hours and 34 minutes, the event sequence produced 31 earthquakes, with magnitudes ranging from -0.5 to 2.6 and focal depths between 0 and 8 km. The swarm exhibited a typical pattern of clustered, low-magnitude activity without a dominant mainshock, consistent with fluid migration or localized stress adjustments in the crust.

The earliest event registered at magnitude 0.4 at 1 km depth. Subsequent activity included several events above magnitude 1.0, such as a 2.6 magnitude quake at 2 km depth on 29 January at 22:26 and a 2.4 magnitude event at similar depth shortly afterward. Depths remained predominantly shallow, with most events between 1 and 5 km, suggesting involvement of near-surface crustal structures rather than deeper tectonic processes.

This swarm aligns with the broader seismic character of the region. Morton lies within the southern Washington Cascade Range, where the North American Plate interacts with the subducting Juan de Fuca Plate. The area experiences both volcanic and tectonic influences, including stresses transmitted from the Cascadia Subduction Zone. Shallow swarms in this setting often relate to hydrothermal fluid movement or minor fault slip within volcanic edifices and surrounding sedimentary basins.

Historical records indicate five prior swarms in the immediate vicinity since 2000, occurring in 2000 (one swarm), 2004 (two swarms), 2005 (one swarm), and 2008 (one swarm). These episodes share similar traits of numerous small-magnitude events concentrated over short time windows, reinforcing the recurrent nature of swarm-type seismicity south of Morton.

Analysis of event timing shows peak activity during the first 12 hours, followed by a gradual decline. Negative magnitudes reflect the high sensitivity of local networks in detecting microseismicity, providing detailed resolution of swarm evolution. Such sequences contribute to understanding regional hazard by highlighting zones of persistent, low-level strain release.

References

USGS Earthquake Hazards Program – Pacific Northwest seismic monitoring data
Pacific Northwest Seismic Network – Cascade Range swarm documentation
Washington State Department of Natural Resources – Geologic mapping of Lewis County