Moderate earthquake close to Cobb Mountain and The Geysers geothermal project, Northern California

Last update: March 14, 2013 at 6:22 pm by By Ashish Khanal

Preliminary Magnitude M4.6 at a shallow depth of 2 km.
The epicenter area is mainly a wilderness area, with only some isolated houses.
We do not expect any damage because of the relatively big distance to the nearest villages (considering the Magnitude).
This area has no historic record (since 1900) of a major earthquake.
Cobb (2000 inhabitants) is expected to have experienced a light shaking and Cloverdale (9000 inhabitants) a weak shaking. Other locations in the area a very weak shaking, probably only felt by a very limited number of people.
Santa Rosa : a (theoretically) “not to be felt” shaking

5km (3mi) WSW of Cobb, California
21km (13mi) SW of Clearlake, California
23km (14mi) NNE of Healdsburg, California
29km (18mi) N of Windsor, California
115km (71mi) WNW of Sacramento, California

Most important Earthquake Data:

Magnitude : 4.2

Local Time (conversion only below land) : 2013-03-14 02:09:00

GMT/UTC Time : 2013-03-14 09:09:00

Depth (Hypocenter)  : 4 km

Update 18:20 UTC : We have pulled the following “I Have Felt It” report out of the many we received as it came from the epicenter area itself :

March 14, 2013 I awoke to the worst shaking and rumbling I have felt in the 8 and half  years that I have been living in Cobb California.  I am used to the shaking but this was different.  For the first time I wondered if I should get out of the house. There was a second shaking 5 to 10 seconds later and rumbling in the distance for 30 seconds more.

Update 11:41 UTC : It looks like this earthquake has some links with the geothermal project at the nearby The Geysers. The extremely shallow location of the hypocenter (2 km) is another indication of this theory.
Read carefully the text of The Geysers below as we might have set a record today.

The Geysers
The Geysers is a complex of 22 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains 72 mi (116 km) north of San Francisco, California. The largest in the world, the Geysers has 1517 MW^[1] of active installed capacity with an average production factor of 63% (955 MW).Calpine Corporation operates and owns 19 of the 22 active plants in the Geysers and is currently the United States’ largest producer of geothermal energy. Two other plants are owned jointly by the Northern California Power Agency and the City of Santa Clara’s municipal Electric Utility(now called Silicon Valley Power). The Bottle Rock Power plant owned by the US Renewables Group was expected to be reopened in 2007. Another plant is under development by Ram Power Corp, formerly Western Geopower, with operation set to begin in 2010. Since the activities of one geothermal plant affects those nearby, the consolidation of plant ownership at The Geysers has been beneficial because the plants operate cooperatively instead of in their own short-term interest.

Seismicity at The Geysers
Current studies of The Geysers Geothermal Field seismicity have reached the conclusion that deep-well injection in the field produces mostly microseismic events between magnitude 0.5-3.0 on the Richter Scale (M).
Worldwide, the largest induced seismic event to date linked to Enhanced Geothermal System (EGS) activity was M3.7 in the Cooper Basin of Australia. However, research based on maximum fault lengths indicates that a M5.0 is the largest possible (but not probable) event in the Geysers.
A concern to the residents is not only the amount of seismicity but the magnitude of the largest seismic event likely to occur. Although no one can accurately predict earthquakes, the magnitude of an earthquake is dependent on the surface area that can slip — the length times the depth or width of the fault. Therefore, a large earthquake can occur only on a large fault. There are no mapped faults of large length in The Geysers, so it is extremely unlikely that induced seismicity caused by activities in The Geysers will lead to a large earthquake.

Future
The Geysers electrical plant reached peak production in 1987, at that time serving 1.8 million people. Since then, the steam field has been in gradual decline as its underground water source decreases. Currently, the Geysers produce enough electricity for 1.1 million people.
Techniques developed from Enhanced Geothermal Systems research will increase the production of the region in the future. By reinjecting greywater from the nearby city of Santa Rosa, existing wells will be recharged. This water will be naturally heated in the geothermal reservoir, and be captured by the existing power plants as steam. The project should increase electrical output by 85 MW, enough for about 85,000 homes. (source Wikipedia)

One of The Geysers geothermal plants – Image courtesy Wikipedia

Update 09:36 UTC : Contrary to what we wrote below, this quake may have been felt a little stronger than expected as we received a readers experience from Santa Rosa, stating : “i was watching tv and i felt everything slightly moving. It was a surprise for me”

from:    http://earthquake-report.com/2013/03/14/moderate-earthquake-75-miles-w-of-sacramento-california-on-march-14-2013/