Information Statement for the November 2-10, 2009, Lassen Peak swarm activity

U.S. Geological Survey ^ | Nov 17, 2009 | USGS

[dan_s]

Current Update, last updated Nov 17, 2009 11:16 PST:
Information Statement for the November 2-10, 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.

Volcanic History Overview: The Lassen volcanic center consists of the andesitic Brokeoff stratovolcano SW of Lassen Peak, a dacitic lava dome field, and peripheral small andesitic shield volcanoes and large lava flows, primarily on the Central Plateau NE of Lassen Peak. A series of eruptions from Lassen Peak from 1914 to 1917 marks the most recent eruptive activity in the southern Cascade Range. Activity spanning 600,000 years began with construction of Brokeoff stratovolcano. Beginning 400,000 years ago activity shifted to the north flank of Brokeoff, where episodic, more silicic eruptions produced a field of a dozen dacitic lava domes including Bumpass Mountain, Mount Helen, Ski Heil Peak, and Reading Peak. At least 12 eruptive episodes took place during the past 100,000 years, with Lassen Peak being constructed about 28,000 years ago. The Chaos Crags dome complex was constructed about 1100-1000 years ago north of Lassen Peak. The Cinder Cone complex NE of Lassen Peak was erupted in a single episode several hundred years before present and is considered part of the Lassen volcanic center (Clynne et al., 2000). The 1914-1917 eruptions of Lassen Peak began with phreatic eruptions and included emplacement of a small summit lava dome, subplinian explosions, mudflows, and pyroclastic flows.

[Erik Latranyi]

6,6 Quake Rocks Canada's West Coast

Coincidence?

[sportutegrl]

This may be a stupid question, but is this related in any way to the recent earthquake in British Columbia, Canada?

[tubebender]

This is just the Libs shaking under the bed when they heard that Sarah Palin will be at the Sierra Cascade Logging Show in Redding show early next year. I just bought a postcard with a photo of the May 22 1915 eruption depicting a classic mushroom ash column...

[tubebender]

This one makes me very nervous as that is on the north end of the Cascade subduction zone that has its beginnings off shore about 50 miles SW of Humboldt Bay and was the cause of a 9.1 tremor in 1799 and no... I was not witness to that regardless what others are saying about me...

[editor-surveyor]

They have no reason to fear of course, she’s irrelevant you know....

[SouthTexas]

LOL. The first thing I think of when I see “swarm” is killer bees.

Sure glad the earth doesn’t move down here.