SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — A University of Hawaiʻi at Mānoa-led study published in the peer-reviewed Journal of Geophysical Research: Solid Earth says tectonic stress along the San Andreas and San Jacinto fault systems in Southern California has reached, and in some places exceeded, the highest levels seen in the past 1,000 years.
The authors say the findings have direct implications for seismic hazard assessments in a densely populated corridor that includes the Inland Empire, Los Angeles and the Coachella Valley. The study was led by Earth scientists at the University of Hawaiʻi at Mānoa, with lead author Liliane Burkhard identified as a research affiliate in the Hawaiʻi Institute of Geophysics and Planetology at the UH Mānoa School of Ocean and Earth Science and Technology and as a scientist at the University of Bern in Switzerland.
According to the study, the stress build-up is not limited to one fault trace. The reconstruction covers the San Andreas and San Jacinto systems together, reflecting the way stress can move through connected fault segments across Southern California.
In its findings, the study says modeled stress reached 3.6 MPa on the San Jacinto-Bernardino section, the highest value in the 1,000-year simulation, and 2.8 MPa on the neighboring Mojave South section of the San Andreas Fault. The authors said those levels place the region in a state that, in their reconstruction, matches or exceeds the peak stress seen anywhere during the past millennium.
The paper also points to Cajon Pass as a place that could help a rupture move through both fault systems at once. In the study’s framing, that would create a joint rupture rather than a failure on only one fault.
The University of Hawaiʻi release said such a joint rupture could be significantly more damaging than a single-fault event. The areas named in the release as potentially affected include Los Angeles, San Bernardino, Riverside and the Coachella Valley.
Burkhard said the team’s results show stress levels on multiple fault segments are now at or above the highest values seen in the past millennium and that the region may be capable of a large through-going rupture involving both fault systems.
“Right now, with stress at historically high levels across the region and more than 160 years elapsed since the last major rupture, the system is in a critically loaded state,” Burkhard said in the release.
The study compares present-day tectonic stress with conditions reconstructed over about 1,000 years, giving researchers a long view of how strain has accumulated across the fault network. The release says that long-term perspective matters because the San Andreas and San Jacinto systems have both been quiet for more than 160 years since the last major rupture.
The work adds to long-running concern about how stress may transfer between major faults in Southern California, where several large population centers sit near active seismic systems. The study’s authors say that makes the findings relevant not only for earthquake science, but also for hazard planning across the region.
The University of Hawaiʻi release says the study was published in Journal of Geophysical Research: Solid Earth, indicating the work has passed peer review. It identifies Burkhard as the lead author and says the research was done by Earth scientists at UH Mānoa.
The study’s main finding is that the fault system spanning the Inland Empire and the broader Southern California region is now loaded at levels comparable to, and in some places beyond, the highest stress seen in the past 1,000 years. The authors say that makes a through-going rupture involving both the San Andreas and San Jacinto faults a possibility worth taking seriously in seismic hazard assessments.
