Federal scientists at the US Geological Survey have raised the estimated chance of a major earthquake striking California's Bay Area to 74.1 percent by 2055.
The updated forecast represents the first regional assessment revision since 2014, when the probability of a magnitude 6.7 or stronger quake occurring within the next three decades was calculated at 72 percent.
Scientists warned that a seismic event of that magnitude could inflict widespread destruction on homes, roads, and critical infrastructure across the heavily populated metropolitan area.
Tectonic stress has continued to accumulate beneath Northern California because years have passed without a major fault rupture releasing the strain.
US Geological Survey seismologist Ned Field told the San Francisco Chronicle that fault conditions in the region are increasingly critical. "Things seem to be pretty locked and loaded," Field said. "We’d be wise to be ready."
The US Geological Survey is the principal scientific agency of the United States federal government responsible for studying natural hazards, mapping geological structures, and monitoring earthquake activity. California lies along a major tectonic boundary where the Pacific Plate and North American Plate slide past each other, creating a complex network of active faults capable of generating severe ground shaking.
Historical impact and population exposure
The Bay Area last experienced a major destructive earthquake in 1994, when a magnitude 6.7 quake centered in Northridge struck.
That event, known as the Northridge Earthquake, caused at least 57 fatalities and left thousands of people injured.
Property damage from the 1994 earthquake reached up to $20 billion, with an additional $40 billion in economic losses, making it the costliest earthquake disaster in United States history.
Around 7.7 million people live across the nine counties that make up the San Francisco Bay Area, while a broader metropolitan definition reaches over nine million residents.
The San Francisco Bay Area anchors Northern California's economy and includes major urban centers such as San Francisco, Oakland, and San Jose. Given the dense population, scientists note that the primary question facing millions of residents is not whether another destructive earthquake will strike, but when.
Updated forecast models and fault probabilities
Researchers derived the latest probabilities using the third Uniform California Earthquake Rupture Forecast, the same statewide seismic model used for the 2014 assessment.
The Uniform California Earthquake Rupture Forecast calculates which faults could produce earthquakes of varying magnitudes and estimates the likelihood of those events occurring.
For the latest assessment, researchers advanced the model's starting point to 2026, allowing it to factor in the additional years that have passed without certain fault sections rupturing, the San Francisco Chronicle reported.
An earthquake counts toward the Bay Area estimate if any portion of its rupture enters a designated zone extending roughly from Santa Rosa in the north to Monterey in the south.
Santa Rosa serves as the county seat of Sonoma County in the North Bay, while Monterey is located on California's Central Coast.
Analysis of individual faults showed that the Hayward-Rodgers Creek fault system carries the greatest individual risk in the region, with its probability rising from 33.1 percent to 34.3 percent.
San Andreas and Calaveras fault risks
The largest probability increase was recorded along the San Andreas Fault, where the odds jumped 3.6 percentage points, from 21.9 percent to 25.5 percent.
The San Andreas Fault is a major transform fault extending approximately 800 miles through California, forming the primary boundary between the Pacific and North American tectonic plates.
The Calaveras Fault now has a 26.8 percent probability of producing a major earthquake, up from 25.6 percent.
The Calaveras Fault runs east of the Hayward Fault through the East Bay region, serving as another active branch of the San Andreas fault system.
Warnings of global seismic wave transfer
A scientist who has accurately predicted earthquakes in the past recently warned that a massive seismic event could soon lead to a major disaster in the United States.
Geophysicist Stefan Burns claimed that California was now firmly "in the crosshairs" for a massive and devastating earthquake along its most vulnerable faults, including the San Andreas.
Burns warned during a livestream on YouTube that the entire state faces heightened risk. "California is super overdue," Burns warned. "What areas in California are now at greater risk? In general, just all of California but really more Southern California would be at greater risk because of this."
The scientist explained that energy released during the magnitude 7.4 earthquake in San Jose Del Palmar does not stay local.
Those seismic waves and stress changes travel through the Earth and can load geological faults thousands of miles away with more pressure that will eventually cause more earthquakes.
Burns specifically singled out the United States, noting that major earthquake hotspots such as the West Coast and the New Madrid Seismic Zone in the Midwest may be activated by the deadly quake that has killed at least 132 people.
The New Madrid Seismic Zone is a major intraplate seismic zone located in the central United States, spanning parts of Missouri, Arkansas, Tennessee, Kentucky, and Illinois.
He warned that the next six to 12 months will be a critical time, especially in California, as many mega earthquakes throughout recent history have occurred within months of each other.
"It's that six [month] to one year time frame that we're worried about, and if we get kind of past that then maybe we can start to breathe a bit of a sigh of relief," Burns said. "But because we've been seeing so much activity in Northern California, it's hard to rule out Northern California. So really all of California is problematic right now."
