Seismologists have revised upward the probability of a catastrophic California earthquake striking within the next three decades.
The new forecast, released through the third Uniform California Earthquake Rupture Forecast, puts the chance of a magnitude 6.7 or stronger quake hitting the Bay Area at 74.1% over the next 30 years, Ned Field, a seismologist with the US Geological Survey, told the SF Chronicle. That figure represents a 2.1% increase from the probability calculated a decade earlier, with scientists attributing the rise to the absence of any major ruptures during that period allowing tension to accumulate across the state’s fault systems.
“Things seem to be pretty locked and loaded,” Field said. “We’d be wise to be ready.”
The San Andreas Fault specifically saw its 30-year rupture probability climb to 25.5%, a 3.6% jump from the 2016 forecast. Meanwhile, the Hayward-Rodgers Creek fault system, which runs through the Bay Area, now carries a 34.3% probability of rupturing, marking a more modest 1.2% increase from the previous assessment.
Scientists are tracking particularly alarming stress levels in Southern California. The tectonic-plate loading along both the San Andreas and San Jacinto fault systems has reached its highest point in approximately 1,000 years, according to the research.
Ken Hudnut, who helped the US Geological Survey develop seismic resiliency initiatives for California, told National Geographic that the accumulated strain has long been recognized by researchers.
“We all know the San Andreas fault is loaded. It’s ready to go. For years the scientific community has been saying so,” Hudnut said. “Cajon Pass keeps me up at night.”
That geographic chokepoint between the San Gabriel and San Bernardino mountains has emerged as a critical area of concern. Scientists have designated it a potential “earthquake gate,” a location where the geology could either halt a large rupture or permit it to propagate across both the San Andreas and San Jacinto fault systems, potentially generating a substantially more powerful event than either fault would produce independently.
The consequences of a major rupture at Cajon Pass extend well beyond ground shaking. Landslides triggered by such a quake could topple transmission towers and bury critical infrastructure lines. An estimated 75,000 cubic meters of debris could cascade down to block roads through the pass, severing a major transportation corridor. Officials warn that losing access through the pass would significantly disrupt transportation networks, supply chains, communications systems and electrical power distribution across the region.
Former USGS seismologist Lucy Jones told National Geographic that the disaster, while temporally uncertain, remains unavoidable.
“This earthquake’s inevitable. We just don’t know exactly when,” Jones said.
The last major temblor to devastate Southern California struck the Los Angeles area in 1994, when the magnitude 6.7 Northridge earthquake killed dozens, injured thousands, collapsed structures, buckled houses and caused billions of dollars in damage. Another event of comparable or greater magnitude could inflict similar destruction across heavily populated regions.
