SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — A University of Hawaiʻi at Mānoa-led study published in a peer-reviewed journal 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 1,000 years, a finding with direct significance for the Inland Empire.
The research appeared in Journal of Geophysical Research: Solid Earth and was led by earth scientists at UH Mānoa. Lead author Liliane Burkhard is a research affiliate in the Hawaiʻi Institute of Geophysics and Planetology at the UH Mānoa School of Ocean and Earth Science and Technology and a scientist at the University of Bern in Switzerland.
The study said the fault system is now in a critically loaded state after more than 160 years since the last major rupture. The authors said the stress buildup could matter for seismic hazard assessments across a densely populated corridor that includes major Southern California population centers and infrastructure.
“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 of Hawaiʻi at Mānoa release.
For the Inland Empire, the study puts special attention on San Bernardino, Riverside and nearby fault zones tied to the San Andreas and San Jacinto systems. The release said the finding has direct implications for communities and infrastructure in a region that sits close to the mapped fault network.
The researchers said Cajon Pass could help connect the San Andreas and San Jacinto faults in a joint rupture. They said such an event could be significantly more damaging than a rupture on a single fault and could affect Los Angeles, San Bernardino, Riverside and the Coachella Valley.
The study did not present the finding as a forecast that an earthquake is imminent. Instead, it compared present-day tectonic stress with stress reconstructed over the past 1,000 years and found that current levels are at the top end of that history.
According to the study, modeled stress reached 3.6 MPa on the San Jacinto-Bernardino section and 2.8 MPa on the Mojave South section of the San Andreas Fault. The published summary said the 3.6 MPa reading exceeded the highest value seen anywhere in the 1,000-year simulation.
The material released about the study did not include the full model details, the uncertainty ranges attached to the stress estimates, or the exact assumptions used to reconstruct the 1,000-year stress history. It also did not identify the last major rupture by name, date or location.
Burkhard said the present loading level stands out in the record. “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 in the UH Mānoa release.
The paper was published in Journal of Geophysical Research: Solid Earth.
