A recent swarm of earthquakes shook Northern California, putting an uncomfortable spotlight on the region’s lesser-known, but most dangerous geological fault line capable of producing the next “Big One.”
California’s San Andreas Fault gets most of the massive earthquake lore and media attention. There was even a movie — (that had Kylie Minogue make a five-minute appearance, FYI) — about a fictitious quake along it, basically ripping the state apart. However, the region’s riskiest geological fault line in Northern California isn’t the San Andreas Fault, but the lesser-known Rodgers Creek Fault.
On Saturday, September 7th, a 4.3 magnitude tremor shook the ground near Healdsburg around 7 a.m., causing light shaking that was felt as Fairfield, California — over 70 miles from the quake’s epicenter. Soon after, a smaller magnitude 3.9 earthquake hit about a mile away in Lake County; this quake was quickly followed by another tremor with a magnitude of 2.5, making
The quake, itself, wasn’t unusual. An estimated 10,000 to 15,000 magnitude 4.0 to 4.9 earthquakes shake around the globe each year; California, alone, has about 10,000 earthquakes every year, most of which aren’t felt. But what is significant — or at the very least illuminating — is that this past weekend’s swarm of Northern California earthquakes happened along what seismologists believe is the region’s most risky fault line.
Rodgers Creek Fault, which interconnects with the Hayward Fault and the San Pablo Bay, has been estimated to have a 33% chance of producing a 6.7 earthquake over the next 28 years; it’s also believed a quake of that size on the fault could impact the Hayward Fault, causing large aftershocks or even secondary tremors to rip along it, affecting an area populated by some three million people.
To put the Rodgers Creek fault’s violent nature into perspective, there’s only a 12% chance the San Andreas Fault will cause the SF Bay Area’s next “Big One” over the same time frame. Moreover, an earthquake along the Rodger Creek fault has the potential to cause catastrophic damage to the SF Bay Area’s public transit infrastructure.
Unlike the San Andreas Fault, a Rodger Creek-Hayward fault geological event would affect a more intricate network of public roads, highways, subway tunnels, and bus routes. Per the Bay Area Rapid Transit Agency (BART), “very large earthquakes” are capable of cracking the outer shell and concrete liners of the transit tubes — they are expected to crack. Those cracks could take years to fully address and cause BART months defined by network-wide delays.
While we should all count the lucky stars we’ve yet to experience a film-inspiring earthquake worthy of a $110 million budget, let this weekend’s collection of small tremors remind you of the Bay Area’s lattice with multiple fault lines … and finally make an earthquake emergency kit.
Feature image: Screenshot courtesy of USGS
