A magnitude 3.8 quake hit Clear Lake today at around 4:30am north of the normal seismic swarm region. Typically, the Clear Lake geothermal prospect can cause up to 50 small quakes a day, many ranging from 1.0-4.0. 3.8 is a bit larger than the area usually sees, and this quake is different due to its location and size. The area where this quake occurred is at the SE shore of the lake, not near any geothermal drilling or activity. This is most likely a tectonic event and not magma movement, although the area is considered to be an active volcano.
Above image from Google Earth with real-time USGS layer added.
Waveforms of the quake from USGS website.
The Geysers Geothermal Field/Clear Lake area has had an ongoing quake swarm since geothermal power plants were installed on the mountain range south of the lake. This has been going on since the late 1990's. While information on this activity is hard to come by, and the science papers released mostly being from corporate scientists with interests to protect, it is anyone's guess what's going on in this area. The wave forms do appear to be tectonic from this quake (above), so it's probably not a cause for concern. As always though, I will keep my eyes peeled on this location to see if anything new develops (but I'm not going to lose any sleep over it).