Monday, February 13, 2012

4.3 Magnitude Quake Hits Clear Lake/Geysers Geothermal Field

A much larger quake than normal hit the Clear Lakes/Geysers Geothermal Field area on Monday at about 4:30am, in an area that has seen much elevated seismicity since the development of the geothermal field for power plants. This is one of the largest and most productive geothermal energy sites in the world, with smaller quakes being pretty common due to drilling and the pumping of water into the hot rocks beneath the volcanic field. The quake was a magnitude 4.3 and shook up the entire region as you can see in the below screenshot from Google Earth with the USGS overlay/Shakemap overlay.

Google Earth/USGS Overlay screenshot of the quake area with the shake map overlay enabled.

This particular quake was extremely shallow, at less than 0.40km beneath the surface. This quake is most likely a result of the geothermal drilling in the area, although this is a few magnitudes greater than what is normal in the area. Typically, quakes in this region don't exceed much more than a 3.2, and those are pretty rare.

The newly minted CalVO (California Volcano Observatory, formerly Long Valley Observatory) classifies Clear Lake as a high threat based on the surrounding population, history of Holocene eruptions, and the presence of an active geothermal system. It has been added to the new California volcano monitoring system.

It is unclear at this time whether this is purely a geothermal event caused by power plant development, or if this is tectonic (this is an area that is part of the San Andreas fault line), or if this could mean some magma movement below. This area has not had a magmatic or phreatic eruption in a very long time (probably over 10,000 years). The Clear Lake field is classified as active based on geothermal activity, and a large silicic magma chamber provides the heat source used to power the steam turbines at the geothermal plants. So there is magma down there (most likely what scientists refer to as 'crystal mush'), but it is apparently much too cool to erupt.

This event was not likely related to dike intrusion or injection of fresh magma (the event was much too shallow), and more than likely is a result of underground steam explosions or rock fracturing/slippage. If any USGS analysis comes out I'll post a link to it. Keep your eyes on Clear Lake in the meantime!

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