SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — Earth scientists at the University of Hawaiʻi at Mānoa say 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 finding comes from a peer-reviewed study published in the Journal of Geophysical Research: Solid Earth, according to the university’s news release about the work. Lead author Liliane Burkhard, 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, led the study.
For the Inland Empire and the rest of inland Southern California, the paper points to a fault system that the authors describe as critically loaded. The release says more than 160 years have passed since the last major rupture in the system.
Burkhard and her colleagues said their results show stress levels on 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 release.
The study said the highest modeled stress reached 3.6 megapascals, or MPa, on the San Jacinto-Bernardino section, above the top value seen anywhere in the 1,000-year simulation. It also reported 2.8 MPa on the nearby Mojave South section of the San Andreas Fault.
The paper does not, in the information released publicly, set out the full modeling details, uncertainty ranges or the exact date of the last major rupture. But the authors said the pattern is important for seismic hazard assessments in a corridor they described as densely populated and critical to infrastructure.
The release says a joint rupture through Cajon Pass could allow both the San Andreas and San Jacinto faults to break at the same time. The authors said such an event could be significantly more damaging than a single-fault earthquake.
That possible rupture path would affect a wide stretch of Southern California, including Los Angeles, San Bernardino, Riverside and the Coachella Valley, according to the study summary released by the university.
The Inland Empire sits near the southern end of the San Bernardino area named in the study, making the finding especially relevant for communities along the region’s growing urban and transportation corridors.
The San Andreas and San Jacinto systems are among California’s best-known earthquake sources. The new paper adds to concern that stress has continued to build across several linked sections at once rather than easing in one place at a time.
Burkhard said the region’s current loading level, combined with the time since the last major rupture, leaves the system in a critically loaded state.
