USGS finds long-obscured earthquake fault in downtown Santa Rosa

A team from the U.S. Geological Survey in Menlo Park, led by geologist Suzanne Hecker, discovered the fault’s signs throughout the city’s downtown area where redevelopment has long obscured the evidence of past quakes, Hecker said.

The most recent official estimates by the Geological Survey indicate there is a 31 percent probability of a quake with a magnitude 6.7 or greater striking somewhere on the combined Rodgers Creek and Hayward faults in the next 30 years, and recent research has made it clearer than ever that they are linked into a single fault beneath San Pablo Bay.

According to the latest census figures, 174,000 people live in Santa Rosa, the 41-square-mile county seat of Sonoma County.

The newly mapped fault zone in the central part of Santa Rosa is broader and extends farther east than scientists had previously assumed, Hecker’s report said, and her team also found new evidence of a small rightward bend in the fault that defined a slight depression in the ground extending a mile long and a quarter-mile wide.

Precise measurements of that region’s magnetic and gravity variations, as well as the airborne laser technology known as Lidar, also detected a dense magnetic body of rock underground known as an “asperity,” Hecker’s team reported.