SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — A peer-reviewed study led by University of Hawaiʻi at Mānoa 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, a finding with direct relevance for the Inland Empire.
Published in Journal of Geophysical Research: Solid Earth, the paper says the region is now in a critically loaded state more than 160 years after the last major rupture, according to a University of Hawaiʻi at Mānoa news release on the work.
The study’s authors said modeled stress reached 3.6 megapascals on the San Jacinto-Bernardino section, the highest value in the 1,000-year simulation, and 2.8 megapascals on the Mojave South section of the San Andreas Fault.
Those levels matter because the study says Cajon Pass may be a place where the two fault systems could link up in a single through-going rupture. The release said such a joint rupture could be significantly more damaging than a single-fault event.
The scenario described in the paper would extend beyond the Inland Empire, affecting densely populated areas including Los Angeles, San Bernardino, Riverside and the Coachella Valley, according to the release.
“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,” said lead author Liliane Burkhard.
Burkhard is 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, the release said.
“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,” she said.
The study was led by Earth scientists at the University of Hawaiʻi at Mānoa and published in a peer-reviewed journal, meaning the work has completed that stage of scientific review before publication.
The release said the findings have direct implications for seismic hazard assessments in a densely populated and infrastructure-critical corridor in the U.S., with the Inland Empire among the areas singled out by the study’s discussion of fault interaction and possible joint rupture.
For Southern California, the paper’s main conclusion is that the San Andreas and San Jacinto systems should not be viewed in isolation. The authors say the two faults may be capable of acting together, and that possibility is part of the region’s earthquake risk picture as framed by the study.
