Magnitude 4.3 temblor felt in North Bay

"An earthquake measuring at a preliminary magnitude of 4.3 shook Sonoma County on Saturday morning around 9:22 a.m., according to the U.S. Geological Survey. The temblor struck about 3.7 miles north-northwest of the Geysers, close to Healdsburg in the North Bay. Originally the quake was measured at a preliminary magnitude of 3.9 but that was revised to a preliminary 4.3 later in the morning by the USGS."

"While the quake's epicenter was in a relatively rural area, the shaking was felt by people in the wider Bay Area, including San Francisco, Novato and Napa, according to the USGS community map. Earthquakes have been rattling the Bay Area city of San Ramon on and off for months. Earlier in February over 20 quakes were felt in that area. Experts said they believe fluid along small fault lines in the area are likely to have caused the swarm of quakes and it remains unclear when the swarm will definitively be over."

"The Geysers is an extremely seismically active place and known for its geothermal field where steam is used to power electric plants. By withdrawing steam and heat from the ground, it's possible these plant operators are setting off the small quakes, according to the USGS FAQ. While California is known for fault lines capable of producing massive and devastating quakes with a high magnitude, the USGS believes the largest quake that could hit the Geyers is likely a magnitude 4.5 temblor."

An earthquake with a preliminary magnitude of 4.3 struck Sonoma County around 9:22 a.m., centered about 3.7 miles north-northwest of the Geysers near Healdsburg. The initial magnitude was reported as 3.9 before being revised upward to 4.3. The shaking was felt across the wider Bay Area, including San Francisco, Novato and Napa. The Bay Area has experienced recent earthquake swarms, particularly in San Ramon, where experts link swarms to fluid movement along small fault lines and cannot say when swarms will end. The Geysers geothermal field may produce small quakes from steam and heat withdrawal, and the USGS estimates the largest likely Geysers event at about magnitude 4.5.

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