April 15, 2019– Mary Greeley News – A 4.2 magnitude earthquake struck in the geothermal generation site of northeast Sonoma County early Monday morning, according to the United States Geological Survey.
It was downgraded to a M4.1
The quake hit at 4:54 a.m. and was less than a mile deep, the USGS said. It was centered 14.6 miles away from Healdsburg and 18.5 miles away from Windsor. The epicenter was a few miles away from Cobb Mountain in Lake County.
The Geysers is the world’s largest geothermal field, containing a complex of 22 geothermal power plants, drawing steam from more than 350 wells, located in the Mayacamas Mountains approximately 72 miles (116 km) north of San Francisco, California.
Gravity and seismic studies suggest that the source of heat for the steam reservoir is a large magma chamber over 4 miles (6.4 km) beneath the surface, and greater than 8 miles (13 km) in diameter.
Steam to power extraction had begun to deplete the Geysers steam field and production began to drop.
However, since October 16, 1997, the Geysers steam field has been recharged by injection of treated sewage effluent, producing approximately 77 megawatts of capacity in 2004.
Before 1969, there were no earthquakes above magnitude 2 recorded by the United States Geological Survey (USGS) in an approximately 70 square miles (180 km2) area around the Geysers. Studies have shown that injecting water into the Geysers field produces earthquakes from magnitude 0.5 to 3.0, although a 4.6 occurred in 1973 and magnitude four events increased thereafter.
credit: In part with https://en.wikipedia.org/wiki/The_Geysers