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, with possible implications for the Inland Empire and other parts of the region.
The research was published in Journal of Geophysical Research: Solid Earth, indicating the study has completed journal peer review. The 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 university said the work has direct relevance for seismic hazard assessments in a densely populated and infrastructure-heavy corridor. The study focuses on the San Andreas and San Jacinto fault systems, two of the best-known earthquake sources in Southern California.
“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.
The study’s authors also said the fault system is in a critically loaded state. “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 model described in the research, stress reached 3.6 MPa on the San Jacinto-Bernardino section, a level the summary says exceeded the highest value seen anywhere in the 1,000-year simulation. The study also found 2.8 MPa on the neighboring Mojave South section of the San Andreas Fault.
The authors said Cajon Pass could help a joint rupture of both the San Andreas and San Jacinto faults at the same time. Such a rupture, they said, could be significantly more damaging than a single-fault event.
The study said the possible impacts would reach across densely populated areas including Los Angeles, San Bernardino, Riverside and the Coachella Valley. That makes the findings especially relevant for Southern California’s inland communities, where transportation routes, housing and other infrastructure sit near the fault systems.
The research adds to a long-running scientific effort to understand how stress builds on major faults and how that stress may shape earthquake hazard. The study does not say when a major earthquake would happen, but it frames the region as one where fault segments have loaded to levels comparable with, and in some places above, the highest levels reconstructed over the past millennium.
Burkhard and the other authors said the finding matters because it points to the possibility of a through-going rupture across more than one fault system, rather than a rupture limited to a single segment. The study says that scenario could produce more severe damage than a single-fault event.
For the Inland Empire, the study’s focus on San Bernardino, Riverside and Cajon Pass places the region near the center of the hazard picture described by the authors. The paper says the San Andreas-San Jacinto system could affect Los Angeles, San Bernardino, Riverside and the Coachella Valley.
