Key Takeaways
- Stress on the San Andreas and San Jacinto faults is higher now than at any point in the last 1,000 years.
- The prolonged quiet period since the 1857 Fort Tejon quake has allowed strain to build, making a large earthquake increasingly likely.
- The Cajon Pass may act as an “earthquake gate,” potentially letting a rupture jump between faults and affect millions more people.
- Preparedness—emergency kits, communication plans, evacuation routes, and public education—is the most effective defense.
- While the exact timing is unknown, experts agree a significant quake is inevitable within our lifetimes.
A new study warns that Southern California faces an elevated risk of a major earthquake, with stress on the San Andreas and San Jacinto faults now higher than at any point in the last millennium. Researchers say the long quiet period since the 1857 Fort Tejon quake has allowed strain to accumulate, making a large rupture increasingly likely. The findings serve as a reminder that residents must stay prepared for the inevitable “Big One.”
The study, led by Liliane Burkhard of the Hawaiʻi Institute of Geophysics and Planetology and co‑authored by USGS geologist Kate Scharer, used geological records such as tree‑ring widths and sediment layers to reconstruct fault stress over the past thousand years. By feeding this data into a computer model, the team simulated how pressure builds on the San Andreas‑San Jacinto system and compared the result to present‑day conditions. Their analysis shows that current stress levels exceed any previously modeled point in the last 1,000 years.
Harold Tobin, director of the Pacific Northwest Seismic Network, noted that while the idea of a stressed fault zone has long been suspected, this research provides a quantitative, rigorous foundation for those concerns. The model’s output confirms that the accumulated strain is sufficient to trigger a large‑magnitude earthquake should the faults rupture. In essence, the southern segment of the San Andreas and the adjacent San Jacinto fault are now in a critically stressed state, primed for release.
A key focus of the study is the Cajon Pass, the narrow corridor between the San Gabriel and San Bernardino mountains. Researchers describe it as a potential “earthquake gate” that can either stop a rupture or allow it to jump from the San Andreas to the San Jacinto fault, depending on the prevailing stress conditions. If the gate opens, the seismic energy could travel farther south, impacting densely populated areas such as the Coachella Valley and San Bernardino County, thereby increasing the number of people at risk.
Preparedness remains the most effective defense against a major quake. Experts recommend that every household assemble an emergency kit containing at least 72 hours of water, non‑perishable food, and any necessary medications. A communication plan—including out‑of‑area contacts and a reunification strategy—is vital because cell networks often fail immediately after shaking. Knowing evacuation routes, securing heavy furniture, and practicing drop‑cover‑hold‑on drills can further reduce injury and loss.
Kate Scharer of the USGS points residents toward resources such as the Earthquake Country Alliance for detailed guidance on retrofitting homes and assembling kits. Meanwhile, USC professor Ahmed Elbanna highlights the value of public education, suggesting that listeners tune into LAist’s “The Big One” podcast to deepen their understanding of seismic science and preparedness strategies. Both experts agree that informed citizens are better able to act quickly when the ground starts to move.
Scientists stress that while the timing of the next large earthquake remains uncertain, timing of the next large earthquake remains uncertain, its occurrence is inevitable on geological timescales. As Elbanna notes, the quake could strike today, tomorrow, in a decade, or three decades from now—all of which are brief intervals compared to the millennia over which fault stress accumulates. Scharer adds that residents should therefore expect to experience a significant quake at some point during their lifetimes and plan accordingly.
In summary, the new research underscores that Southern California’s fault network is under unprecedented strain, with the Cajon Pass acting as a potential conduit for a widespread rupture. While experts cannot predict the exact day of the next Big One, they agree that preparation—through emergency supplies, communication plans, and public education—is the best way to mitigate harm. Staying informed and ready remains the community’s most powerful tool against the inevitable seismic threat.
