#19,013
While the United States has enjoyed a bit of an earthquake drought the past century, the good news (and bad) is that all droughts eventually end.
Exactly where and when that break will occur is unknown, but in 2024 the USGS unveiled a new seismic risk map (see below), increasing the percentage of Americans at risk of experiencing a damaging earthquake to nearly 75% (roughly 240 million people).
Additionally, there are nearly a dozen `very high risk' volcanoes in the continental US (4 in Washington, 4 in Oregon & 3 in California), along dozens of `lesser' threats. While earthquake damage is generally localized, volcanic eruptions can affect property and populations thousands of miles away.
And as we've explored previously, while a truly `Big One' in California would have huge physical impacts locally, it could also be devastating to the entire U.S. economy (see Dr. Lucy Jones: `Imagine America Without Los Angeles’).
"The study is not a prediction of when an earthquake will occur. What we can say is that the system is critically stressed and that physics-based models like ours give a clearer picture of the range of scenarios we should be prepared for. This information is important for hazard assessment, infrastructure planning and emergency preparedness."
First a look at the abstract and summary from the study. While a lot of this report is technical, many will want to read it in its entirety.
Liliane M. L. Burkhard, Bridget R. Smith-Konter, Katherine M. Scharer, David T. Sandwell
First published: 03 June 2026 https://doi.org/10.1029/2025JB033213Digital Object Identifier (DOI) view metrics
Abstract
With over a century since the last major rupture affecting the wider Los Angeles region, tectonic stress has steadily built along the southern San Andreas and San Jacinto fault systems, raising concerns of an imminent large earthquake. Cajon Pass, located at the junction of these faults, represents a critical site for potential through-going ruptures in Southern California. We constructed new 4D earthquake cycle simulations using a 1000-year paleoseismic rupture history of the San Andreas Fault System (SAFS) to assess spatial and temporal variations in stress. A semi-analytic Fourier transform model was used to compute stress from 3D dislocations in an elastic plate overlying a Maxwell viscoelastic half-space, assuming a complete coseismic reset of resolved shear stress on ruptured elements.
Results show highest stress accumulation north of Cajon Pass (∼1.8 MPa/100 years) due to greater slip rates, and lower rates south of Cajon Pass (∼1.0–1.5 MPa/100 years). By 2025, Coulomb stress is estimated at 2.8 MPa on the Mojave South (MOS) segment, 1.8 MPa on the North San Bernardino (NSB1) segment and 3.6 MPa on the San Jacinto Bernardino (SJB) segment. Segments accumulate stresses with characteristic ranges of pre-event stress interpreted as failure thresholds: 1.2–2.7 MPa for MOS, 0.4–1.6 MPa for NSB1, and 1.2–2.9 MPa for SJB. When the stress disparity between segments SJB and MOS narrows, the faults appear to rupture jointly, suggesting that stress levels may control how Cajon Pass acts as an earthquake gate. These results may inform seismic hazard assessments by linking stress evolution to fault interactions.
Plain Language Summary
Southern California's San Andreas and San Jacinto faults have not produced a major earthquake near Los Angeles in over a century. During that time, tectonic stress has continued to build along these faults, increasing the likelihood of a large future rupture. One key area of concern is Cajon Pass, where the two fault systems meet and could potentially rupture together.
To investigate this, we used computer simulations of the last 1000 years of large earthquake activity to estimate how stress builds up on fault segments and affects neighboring segments over time. The model shows that stress has now reached high levels across the region and that the two fault systems may interact when their stress levels become similar. This suggests that Cajon Pass could act as an “earthquake gate” which sometimes blocks and other times allows large ruptures to propagate between faults. These results improve our understanding of earthquake interactions in Southern California and help refine regional hazard assessments.
Regardless of whether the next `big one' occurs on one fault or two, its impact could be substantial, and it is important to be prepared. Every year since 2009 I've promoted Shakeout.org's safety campaign, and I strongly urge anyone who lives in any seismically active region to take part.
While the government will send help, you could find yourself pretty much on your own for several days and living in less than comfortable conditions for weeks.
Many agencies and organizations in the U.S. recommend that households work towards having a 10-to-14 day supply of food, water, and emergency supplies on hand, which I consider far more prudent.
