An earthquake registering at 4.4 shook Santa Rosa and surrounding communities at 6:39 p.m. Sept. 14. A second quake with a magnitude of 4.3 followed 42 seconds later.
Authorities reported the earthquakes happened at the Rodgers Creek Fault, which last had a significant earthquake around the 1700s. The fault is estimated by seismologists to rupture every 230 years, on average, with previous intervals ranging from 131 to 370 years.
The fault builds up strain at a rate of close to ten millimeters (0.4 inches) per year, which means that since the 1700s, it has accumulated around two to three meters (seven to ten feet) of strain that will be released in the future.
The jolts were another reminder that earthquake season is an all year event.
Get Ready Marin will offer a class on how to prepare when disaster strikes – including earthquakes – on Oct. 18, at 6:45 p.m. at All Saints Church in Novato, 2 San Marin Drive.
No significant damage was reported, though it was strong enough to knock pictures off of walls and crack water pipes.
The U.S. Geological Survey said Rodgers Creek Fault runs under the Hidden Valley neighborhood near Fountaingrove in northeastern Santa Rosa.
The USGS said the earthquakes originated roughly 3.5 miles underground. The Rodgers Creek Fault is the northern spur of what becomes the Hayward Fault. The last major eruption of the Hayward was in 1868.
How do you measure the depth?