Monday, October 31, 2011

Sierraville CA Earthquake Swarm is Magma Dike Intrusion

Sierraville, CA

Sierraville CA has been experiencing some activity in an area not known for any recent previous volcanism. Over 100 small earthquakes shook the region last week, and this week a mag 4.7 with about 9 or so aftershocks rumbled the area on the 26th. Seismologists have been quoted as saying "What we think is happening is magma is being injected into the upper most mantle, right at the base of the crust and magma is starting to lift up the whole area."

This of course does not mean that a volcanic eruption will occur, but it does of course raise that chance.

The quakes have ranged from 20km - 12km in depth, still far from the surface. In many occasions (and you can really see this process in older more erosion-sculpted areas of the planet) dike intrustion stops there. What a dike intrusion is, is a fracture in the crust that is filled by magma. Sometimes this magma cools, and when eroded, creates a spectacular natural wall after the elements and uplift exposes the dike. In other cases, (this is more common in Iceland) dike intrusion leads to fissure eruptions.

The Sierraville quakes at this point are scientifically interesting, but probably pose little to no immediate threat. However, since these swarms have now been going on for a few weeks, it's definitely worth keeping an eye on, as this area is close to several other volcanic centers like Steamboat Springs, and Soda Lakes in Nevada. Anything is possible!

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