TA: Great thread! And my hometown made your map! Woo Hoo!
I grew up in Cloverdale, CA through the 70's and 80's. Many friends' parents worked at the Geysers, and many of those old classmates work up there
today. I'm going to throw some pros and cons against the wall for your consideration, but for the record I agree that induced seismicity definitely
occurs at the geysers...I have friends on the hill who feel the shaking!
First off: That fault system has been active for quite a while, pre-dating the geysers injection processes. While there is no doubt that induced
seismicity occurs at the geysers, the geologic conditions of the area prohibit anything more than a 5.0 on the Richter scale. This is due to two
First, The geysers sit above a near-surface magma chamber, roughly 5-6 km below the surface. This depth limit prevents the large scale buildup of
tensions that cause major earthquakes. The magma chamber also heats the rocks. When rocks get hot they lose structural integrity... become less
brittle and more viscous. This state also works against large energy buildup. Soft rocks fail at much lower energy levels than brittle cold
Second, none of the faults in the Geysers area are significant enough to produce a notable earthquake. The region is crisscrossed with a jumble of
small faults, but none have any impact on large scale geologic activity.
As for injection history:
The geysers began the reinjection process in 1970, recycling "spent geothermal fluids" back into the production zone. While I don't have figures on
volume, I imagine it wasn't an amazing amount.
After a peak in production around 1987 (~1.8 mil homes powered), the volume of geothermal fluids began a steady decline. They were running out of
steam, literally. In 1995 a pipeline project began ( Lake County-Southeast Geysers Effluent Pipeline Project) which transported 8 mil gal / day of
greywater to be reinjected into the production zone. That project was considered successful, and, in 2003, the Santa Rosa Geysers Recharge Project
began operations, transporting 11 mil gal / day to the geysers as well.
As for personal anecdotes:
I knew several Lake County residents in the town of Cobb, who firmly believed that earthquake activity rose once the wastewater injection programs
began pumping. Some folks even went to court due to structural damage to their homes from the repeated earthquakes. Don't know how that turned out,
As a geologist:
Makes perfect sense that a) the slow depletion of fluids from the reservoir would yield less seismic activity (located above the magma chamber, the
rocks are much less brittle than comparable rock in the larger area, bending rather than fracturing) and b) the sudden injection of large fluid
volumes would cause an increase in quakes, as the strata would have zero time to adjust to the changing forces (less brittle, but not taffy).
So TA: I would focus more research on the changes seismically in those key years where large-scale injections began, 1995 and 2003. That would
certainly show some definitive proof that when conditions changed earthquakes ensued, although you may find that the work has already been done
As for the "Save the Planet!", "Fracking is the Devil!" folks...
It's an issue that really comes down to numbers and the stark realities of living in a larger society. The impacted residents might total several
thousand, while the Geysers facilities provide power to 1.1 million people (and has for decades), pretty much the North Coast all the way to Oregon.
Shut down the geysers and not only do you have a HUGE energy crisis, you also get back a couple pretty damn big wastewater disposal problems as
edit on 9-7-2012 by blamethegreys because: REDUNDUNDANCIES