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Seismologists have mapped the Rodgers Creek fault as it passes through Santa Rosa
photo credit: (Credit: Courtesy United States Geological Survey)
A magnitude 3.4 earthquake centered in Santa Rosa shook the region awake at 5:45 this morning.
Suzanne Hecker, a research geologist with the US Geological Survey, said Thursday's small seismic event and twelve smaller ones over the past three weeks in Sonoma County, are normal.
"These earthquakes happen fairly routinely, there might be periods of time where there might be more or less, but these earthquakes happened at a fairly constant rate."
Nearly 1,000 people reported feeling the shaking to the US Geological Survey's 'did you feel it' website. The tremor was felt as far away as Ukiah, Berkeley and San Bruno. According to the USGS, the epicenter was along Caribou Court, just off Mayette Avenue, east of where the freeway segment of State route 12 ends.
While lacking the notoriety of the San Andreas, the Rodgers Creek fault is also capable of violent movement. Hecker, who has extensively researched the fault, which roughly parallels Highway 101, said it produces a magnitude 7.0 about every 300 years. 
While the last big one was about 400 years ago, it's doubtful the next major one is imminent, but it is possible. "Earthquakes don't occur like clockwork. When we look at the frequency of earthquakes in the past, we just get a general sense, but yeah, certainly we're in the time window that we wouldn't be surprised."
Hecker says seismology is still unable to determine if any small quake is a precursor for a larger one.
Recent research suggests the Rodgers Creek fault is connected to the Hayward fault. With the area now urban, a repeat of the Hayward's big 1868 quake could be catastrophic. "It would be highly damaging if there was a magnitude seven point zero or larger in the vicinity of Santa Rosa. Even farther away, and depending on the soil that you're built on, yes, strong shaking could lead to quite a bit of damage in Santa Rosa." 
The quake was at a depth nearly six miles underground.
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