SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — A University of Hawaiʻi at Mānoa-led study 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 implications for the Inland Empire and other heavily populated parts of the state.
The paper was published in Journal of Geophysical Research: Solid Earth, a peer-reviewed journal. It was led by Earth scientists at the University of Hawaiʻi at Mānoa, and lead author Liliane Burkhard is identified as a research affiliate in the Hawaiʻi Institute of Geophysics and Planetology at the UH Mānoa School of Ocean and Earth Science and Technology and as a scientist at the University of Bern in Switzerland.
The study reconstructed tectonic stress across the two fault systems and found that present-day loading is at or above the top end of the past millennium, according to the authors. In the study’s modeling, stress reached 3.6 megapascals on the San Jacinto-Bernardino section, above the highest value in the 1,000-year simulation, and 2.8 megapascals on the Mojave South section of the San Andreas Fault.
The UH release said the findings have direct implications for seismic hazard assessments in a densely populated and infrastructure-critical corridor. The release did not include the study’s full methods, confidence intervals or the assumptions behind the millennium-long stress reconstruction.
The researchers also said the system is in a critically loaded state, with more than 160 years having passed since the last major rupture. The supplied materials did not identify that rupture by name, date or exact location.
Burkhard said, “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.”
The study says Cajon Pass could help a rupture spread between the San Andreas and San Jacinto faults. A through-going break of both faults could be significantly more damaging than a single-fault earthquake, according to the University of Hawaiʻi release summarizing the paper.
That matters for the Inland Empire because the study names San Bernardino and Riverside among the areas that could be affected. The release also says Los Angeles and the Coachella Valley could be in the impact area if both fault systems rupture together.
Burkhard also 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.”
The authors framed the work as a seismic hazard study rather than a short-term forecast, using a 1,000-year comparison to show how unusual the present stress conditions are in their reconstruction. The release did not say when, or whether, a rupture would happen.
The journal publication places the San Andreas and San Jacinto faults in a connected hazard context. The study’s central point is that the two systems may not be best viewed as isolated risks, but as part of a larger rupture path that could matter for emergency planning in Southern California.
For the Inland Empire, that concern is centered on the San Bernardino area and Cajon Pass, where the study says a joint rupture could propagate between the two faults. The release said that kind of event could be more damaging than a break on just one fault.
The UH release said the research was aimed at improving seismic hazard assessments in a corridor where population and infrastructure exposure are high. The paper’s authors said the stress levels they identified are now at, or above, the highest values they found in the past 1,000 years.
The study was published in a peer-reviewed journal, but the supplied materials did not provide the article’s DOI or the exact publication date of the journal paper. The release also did not identify the full set of model inputs used to reconstruct the past millennium of stress.
Even with those limits, the study’s message is clear in the authors’ framing: the San Andreas and San Jacinto fault systems are loaded at historically high levels, and a joint rupture through Cajon Pass remains a scenario of concern for Southern California, including San Bernardino, Riverside, Los Angeles and the Coachella Valley.
