Information Statement for the November 2-16, 2009, Lassen Peak swarm activity

A series of small earthquake swarms beneath the southwest flank of Lassen Peak in Lassen Volcanic National Park that began in the late evening on November 2 continued with sporadic activity diminishing through the 16th. The activity was most intense on the November 3rd with the largest earthquake in the sequence a magnitude M=2.5 event at 1:54 PM (PDT) on the 3rd. These earthquakes are centered some 3 km (2 miles)southwest of the summit of Lassen Peak between Eagle Peak and Mount Diller at a depth of roughly 5 km (3 miles) beneath the surface.

Earthquake swarms are not unusual in this area. Earlier activity in this same area over the last five years includes swarms on March 2009, February 15-16, 2005 (14 events including a M=2.3 earthquake), February 21 2006 (13 events with a M=2.2 earthquake), January 18-19, 2007 (29 events with a M=1.9 earthquake), and September 7-8, 2008 (41 events with a M=2.3 earthquake). This most recent swarm activity appears to be within the norm of earthquake activity detected in the Lassen area since the modern seismic network was installed in 1980. The USGS will continue to monitor the situation closely.



Edited 1 time(s). Last edit at 11/19/2009 04:36PM by eeek.