New simulations show where Bay Area shaking could be worst

The Hayward Fault Line hasn’t had a major earthquake since 1868, but new simulations designed by Lawrence Livermore National Laboratory and Lawrence Berkeley National Laboratory find that the Bay Area’s geography will shape the next “big earthquake,” trapping seismic waves in basins like the Livermore Valley and amplifying the earthquakes’ destructive energy because of the ground beneath them.

Understanding how the “ground motion” generated by an earthquake is amplified as it travels away from the epicenter is critical to preparing Bay Area communities for earthquakes, because damage is determined not only by the size of the earthquake, but how kinetic energy spreads over the terrain and is amplified by the local geology.

“Basins like San Pablo Bay or the bottom of the Livermore Basin will always amplify ground motion, because when (kinetic) waves enter the soft sediment, they transform into larger motion and stay trapped,” said Arben Pitarca, a Lawrence Livermore National Laboratory scientist and co-author of a study published in the journal Seismological Research Letters.

The DOE project, led by Lawrence Livermore National Laboratory with support from Lawrence Berkeley National Laboratory, analyzed the aftermath of a 7.0 magnitude earthquake along the Hayward Fault, combining physics-based rupture models with detailed simulations of wave propagation run on supercomputers to create, “for the first time,” a synthetic database of ground motion, Pitarka said.

The last major earthquake on the Hayward fault line occurred on October 21, 1868. The California Department of Environmental Protection estimates that a major earthquake on the fault line occurs approximately every 140 years, making the fault line overdue. The USGS has since estimated the probability of an earthquake of magnitude 6.7 or greater at 33% by 2043, making the Hayward Fault the most dangerous in the Bay Area.

Archive photo of damage to the San Leandro Courthouse in San Leandro after the 1868 earthquake along the Hayward Fault. (Bancroft Library, University of California, Berkeley)

Earthquakes marked the end and beginning of eras in the Gulf region.

In the 1906 earthquake, the San Andreas fault line moved 32 feet horizontally and left the city of San Francisco engulfed in flames. In 1989, the Loma Prieta earthquake again shifted the fault line 6 feet horizontally and 4 feet upward, causing major traffic arteries through the Bay Area to collapse, according to the U.S. Geological Survey. In preparation for the next big event, scientists are simulating how tectonic shifting on the Hayward fault line will spread across the region.

“Every time there’s a big earthquake, you learn something new,” Petarka said. “The problem we have is that earthquakes don’t repeat themselves.”

Energy from an earthquake does not travel through sediments uniformly. Ruptures occur at different depths, faults carry varying amounts of potential energy, and tectonic plates break at different speeds — each affecting how an earthquake is felt even from a short distance, Petarca said.

These conditions are further complicated by the complex geography of the Gulf region, the study authors wrote. Sharp contrasts across fault lines, such as solid rock in one area and loose sediments in basins such as the Livermore Valley, cause shaking to vary greatly from one area to another. Seismic waves traveling between the Diablo Mountain Range and the region’s valleys create a maze of fluctuating energy.

To study the Bay Area’s seismic ecosystem, the project team ran more than 100 simulations of a typical magnitude 7.0 earthquake along potential locations of the Hayward Fault Line, Pitarca said. The scientists then observed how kinetic energy rippled across the topographic map of the Bay Area in the moments after the quake, using a “heat map” to show where the most violent tremors occurred. In their simulations, seismic waves were more intense in low-lying areas bordering San Francisco Bay and in the Livermore Valley, while energy was dissipated in Berkeley and the Oakland Hills.

“Engineers and seismologists now know what areas could be most vulnerable during an earthquake,” Petarca said. “After every new development, such as this new database, there is always a positive impact on building design codes and a change in technologies that have been put in place to prepare for the major development.”

During the Loma Prieta earthquake, the severity of damage was very localized based on the geology of the soil and the structures built on top. San Francisco’s Marina District, built on an artificial landfill made partly of clay extracted from the Gulf, has been severely damaged by the weak sediments below. The double-decker Cypress Street Viaduct on the Nimitz Expressway in Oakland partially collapsed and was never rebuilt.

The study results are being shared with seismologists and engineers who can use simulated ground motions to test and design buildings, roads, bridges and civil infrastructure when the Hayward fault line ruptures.

A drone view of UC Berkeley’s California Memorial Stadium in Berkeley, California, Thursday, May 21, 2026. The stadium was built directly on top of the Hayward Fault. (Jane Teska/Bay Area News Group)

“The study is another reminder that the Hayward Fault risk is real, significant, and relevant to East Bay residents today, not a remote possibility,” said Janelle Maffei, chief mitigation officer for the California Seismological Service. “Californians have the tools to act now: earthquake early warning, home rehabilitation, and household preparedness all measurably improve resilience.”

The project team is collaborating with the Pacific Earthquake Engineering Research Center in the Bay Area to share data nationally and across the Pacific “Ring of Fire,” the most active seismic region in the world. Participants include early warning developers, public agencies and international researchers, Petarca said. He added that the database already includes hundreds of users around the world.

Meanwhile, Pitarca and other seismology researchers are expanding their scope beyond the Hayward Fault to model earthquakes along other parts of the San Andreas Fault, which runs almost the length of California and can produce earthquakes of magnitude 7.5 or greater.

“We are fortunate that institutions like mine have super-fast computers that have been made available to us to actually simulate this, to understand it a little better, and our duty is to give others what we have learned,” Petarka said.

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