SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — A peer-reviewed study led by University of Hawaiʻi at Mānoa earth scientists 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 research, published in the Journal of Geophysical Research: Solid Earth, focuses on a fault corridor that the authors say has direct implications for seismic hazard assessments in a densely populated and infrastructure-critical part of California.
Lead author Liliane Burkhard, a research affiliate in the Hawaiʻi Institute of Geophysics and Planetology at UH Mānoa’s School of Ocean and Earth Science and Technology and a scientist at the University of Bern in Switzerland, said the study’s results show stress levels across multiple fault segments are now at or above the highest values seen in the past millennium.
“Our results show that 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,” Burkhard said in the university release.
The paper says the region remains in what the authors describe as a critically loaded state, with more than 160 years having passed since the last major rupture on the system.
For the Inland Empire, the study is especially relevant because it names San Bernardino and Riverside among the areas that could be affected if a rupture were to run through both fault systems. The release also identifies Cajon Pass as a place that could help such a rupture move from one fault to the other.
That matters because the study says a joint rupture involving the San Andreas and San Jacinto faults could be significantly more damaging than a single-fault event.
The research team said the modeled stress reached 3.6 MPa on the San Jacinto-Bernardino section, which the paper describes as exceeding the highest value seen anywhere in the 1,000-year simulation. The study also reported 2.8 MPa on the Mojave South section of the San Andreas Fault.
Those figures come from the study’s reconstruction of stress conditions over the past millennium, rather than from direct measurements of strain at a single moment.
The university release said the results show the fault system could be capable of a large through-going rupture involving both fault systems. It said such an event would affect densely populated parts of Southern California, including Los Angeles, San Bernardino, Riverside and the Coachella Valley.
The study’s publication in a peer-reviewed journal means its conclusions have gone through the journal’s review process, though the release did not include the paper’s full methods, uncertainty ranges or modeling assumptions.
The San Andreas fault system is one of California’s best-known earthquake sources, and the San Jacinto fault system has also produced major quakes in the past. The study does not forecast when a rupture will happen, but it places the region’s stress conditions at levels the authors say match or exceed the highest seen in 1,000 years.
Burkhard said the findings show the region may be capable of a large rupture involving both fault systems. The release added that the work was led by scientists at UH Mānoa and published in Journal of Geophysical Research: Solid Earth.
