Along with the upside of world-class wineries, a robust cuisine culture and Sonoma’s location at the birthplace of the Bear Republic, Valley residents have learned to live with the downside: They’re riding along a strike slip fault zone of two of the planet’s major plates that are moving in opposite directions.
And sometimes, like early last Sunday morning, those plates rasp and heave in a seismic shift that leaves property damaged, power lines down and nerves rattled – or worse.
But don’t think that Sunday’s 6.0 (or 6.1) earthquake in Napa in some way inoculated us against another one. That’s the message that Tom Brocher, the director of the USGS Earthquake Science Center, has for Sonoma residents. The opposite, in fact, is the more likely scenario.
There have been three other significant earthquakes in the area, dating back to the so-called San Francisco Earthquake of April 18, 1906 – estimated at about 7.7 on the “moment magnitude scale” that geologists now use to replace the similar Richter scale. Other notable events that have shaken the county include a pair of Oct. 2, 1969, earthquakes just north of Santa Rosa, that measured about 5.7, and the Oct. 17, 1989, Loma Prieta quake (often remembered as the “World Series Earthquake”) of 6.9 MMS.
While the 1989 quake did very little damage locally, the 1906 quake had an even larger destructive impact on Santa Rosa than it did on San Francisco. Many buildings were damaged in the City by the Bay during that quake, but it was the resultant fire that turned the event into a disaster.
In Sonoma County, structural damage was proportionately even greater. A 2005 United States Geological Survey study determined that, in 1906 “the highest ground shaking intensity occurred in and around Santa Rosa, which was more than 20 miles from the rupture zone.” The quake essentially destroyed the downtown area, electricity was cut off for six days, and gas for even longer, and at least 50 people were killed.
For Sonoma Valley residents, the experience was “an awful ordeal,” according to a Sonoma Index Tribute article headlined, “Fearful Visitation of Earthquake,” on the front page of the April 21, 1906, edition.
“The sleeping inhabitants of this valley were ruthlessly awakened to find the earth in the throes of a mighty earthquake which lasted fully one minute. Buildings cracked and partially collapsed, chimneys toppled and roofs fell in. There were the sound of falling glass and the cries of the panic stricken as they rushed pell-mell from their homes to the streets.”
Local destruction in the Valley was primarily to buildings and, according to reporting, no one was killed or notably injured. Several stone buildings suffered collapsed walls, the high school was rendered unfit for use, all the drugs were thrown off the shelves of L.S. Simmons pharmacy and “not a chimney in town is standing,” read the coverage.
It was over 60 years before the next earthquake of significance struck the region, and once again Santa Rosa’s downtown bore the brunt of local damages. The twin Oct. 2 1969, temblors – spaced less than 90 minutes apart – again brought down chimneys and crumbled many older buildings, buckled sidewalks and ruptured underground pipes. In fact, 49 structures, almost exactly half of the 99 damaged buildings in Santa Rosa, were in the downtown area, many of them in the vicinity of Courthouse Square.