Since August 14, Northern California has experienced a surge in seismic activity. The state has documented at least 131 earthquakes since this latest spike began. These seismic events have each been unique in size, with their magnitudes spanning from 0.2 all the way to 4. The most significant earthquake, which had a magnitude of 4, occurred at 5:48 a.m. Pacific time and was centered approximately 10 miles east of Cloverdale.
The U.S. Geological Survey (USGS) seismologists have been keeping a very watchful eye on this strange flourish of activity. That biggest quake hit hardest, in fact, with its epicenter just 20 miles northwest of Calistoga. Interestingly, it is located 26 miles due north of Santa Rosa. Even with all of these alarming earthquakes, experts claim that bigger quakes are not going to occur in the region.
Seismic Hazards in Northern California
Along with the San Andreas fault, Northern California is riddled with fault lines, like the Healdsburg-Rodgers Creek faults. The faults are the largest source of seismic hazard across the highly urbanized Bay Area region. In the Pacific Northwest, recent earthquakes have put a spotlight on seismic risks. Both major fault lines are miles away from the geothermal field where the tremors have most recently been concentrated.
According to the USGS, this geothermal field interaction could be an important factor in the recent seismic activity. The agency noted that withdrawing steam for electric power generation can cause minor earthquakes to occur under the region. This human activity has demonstrable effects on the surrounding ecology.
“Activities associated with the withdrawal of steam for producing electric power cause or induce small quakes to occur in the field.” – USGS
Understanding the Earthquake Dynamics
These earthquakes occurring in Northern California are a combination of three factors. The USGS has indicated that taking away steam and heat from the geothermal field could be a contributing factor to the increased seismicity. Treated municipal cold water reclaimed from Santa Rosa and Lake County and pumped into the Geysers. There, it meets up with a hotter, actively convecting rock layer below, which generates more seismicity.
“The interaction with hot rock appears to be a significant factor in inducing the earthquakes.” – USGS
Experts are still warning that a magnitude 5 or greater earthquake is overdue to hit Northern California. They believe bigger quakes are less likely in the area. According to USGS, we need a big fault for a big earthquake. Currently, there is no evidence of such a feature in the region.
“It is possible that a magnitude 5 could occur, but larger earthquakes are thought to be unlikely. In order for a larger earthquake to occur, it is necessary that a large fault exist.” – USGS
Monitoring and Preparedness
These are the kinds of details seismologists are watching very closely about the small earthquakes. They encourage all residents to remain aware and prepared for any future seismic activity. That’s because most recorded quakes have been too small to feel. The reality of a highly dynamic geological world reasserts itself with the ongoing reminder of Northern California’s complicated seismic tableau.