A magnitude 4.2 earthquake struck about 3 miles northwest of the Geysers geothermal field Wednesday evening and was followed by a series of aftershocks, the U.S. Geological Survey said.

The quakes were reported between 7:58 and 9:04 p.m., according to the USGS. The first was followed by several aftershocks with magnitudes of 4.0, 2.7, 2.7, 2.5 and 2.6.

The first earthquake was felt from Lakeport down to Sonoma and San Francisco, and even as far south as Santa Cruz, according to the USGS. The strongest shaking — Intensity Level 5 — was reported in Geyserville, just south of the epicenter.

Most other areas surrounding the quake felt “weak” shaking, classified as Intensity Level 3. As of 9:50 p.m., the USGS had recorded 200 responses from web users reporting what they felt.

The Geysers region, about 90 miles north of San Francisco, is one of the most seismically active regions in the United States.

Geothermal plants operate as close as 2 miles from the mountain community of Anderson Springs, near the epicenter of the quakes. The USGS says the work associated with the withdrawal of steam for producing electric power can trigger small quakes……more here