Lassen Earthquake Swarm

There is currently an ongoing earthquake swarm in the region immediately south of Mt. Lassen. The largest magnitude is a M 3.9 (USGS). The California Volcano Observatory (CalVO) is monitoring these earthquakes. The earthquakes do not appear to be related to volcanism, but most likely related to the fault systems that strike through that area. These faults are an extension of the Walker Lane fault system, which is a sister of the San Andreas plate boundary. The Walker Lane fault system is a right lateral (dextral) fault system that extends the east side of the Sierra Nevada Mountains. We do not currently know how this part of the plate boundary ends, if it feeds into Cascadia, etc. We have some ideas, but I will leave this a mystery as many of these ideas are unpublished and I do not want to scoop anyone. There are no USGS active faults mapped in this region, but there has been earthquake activity in the Lake Almanor area in the last year or so (see map below from 5/23/13). This region may be an extension of the Butt Creek fault zone (the red faults directly to the southeast of this swarm.

Here is a map of the epicenters in the region of Mt. Lassen.

The CAVO is monitoring these earthquakes, but they clearly state this swarm is related to plate tectonics in the region and not volcanism. Here is a plot of seismicity for this region.

Here is the Did You Feel It map for the M 3.9 earthquake.

The M 3.9 earthquake has a focal mechanism that shows NE-SW extension.

Here is a primer for those who would like to understand focal mechanisms better (from the USGS.

Here is a map I made about some of these Almanor earthquakes.

Category(s): College Redwoods, earthquake, education, geology, plate tectonics, San Andreas

8 Responses to Lassen Earthquake Swarm

  1. Can’t be right Jay. Fifth grade science class taught us this is a totally dead volcano. It was written in the book.

  2. lassen is NOT dead. it last erupted about a century ago…

    but if you read my post, these are plate tectonic earthquakes, unrelated to volcanism.

  3. I’m having a tongue in cheek moment. I questioned it then and was shut down because it was in the book

  4. Not too far from the large earthquake about a year ago. Looks like the swarm projects NW along the same fault trace.

  5. indeed, the swarm along the east side of lake almanor… (i put a map of that swarm on my post)

  6. why did you change you name to bird? where you premeditating the roast in the fire?

  7. i was playing around with changing my fb name, but my name did not really change and now i am stuck with jay bird for 2 months… ugh.

    ppl used to call me jay bird sometimes…

One Response in another blog/article

  1. […] was a swarm near Mt. Lassen in November 2014. I posted about this swarm at the time here. Here is a map showing that […]

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