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 Southern California’s San Andreas and San Jacinto fault systems has reached, and in some places exceeded, the highest levels seen in the past 1,000 years.
The research, published in the Journal of Geophysical Research: Solid Earth, was described by the authors as directly relevant to earthquake hazard assessments in a densely populated corridor that includes the Inland Empire, Los Angeles, Riverside, San Bernardino and the Coachella Valley.
Lead author Liliane Burkhard, a research affiliate in the Hawaiʻi Institute of Geophysics and Planetology at the University of Hawaiʻi at Mānoa School of Ocean and Earth Science and Technology and a scientist at the University of Bern in Switzerland, said the study finds stress on multiple fault segments is 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 a university release.
The study’s authors said the system is in a critically loaded state after more than 160 years since the last major rupture. The release said that finding matters because the San Andreas and San Jacinto systems are among the faults most closely watched by earthquake scientists in Southern California.
The work was led by Earth scientists at the University of Hawaiʻi at Mānoa and published in a journal that uses peer review, giving the results an added layer of formal scientific review before publication.
According to the university release, the study points to Cajon Pass as a location that could help a joint rupture move through both fault systems at once. The authors said such a rupture could be significantly more damaging than a single-fault event.
For the Inland Empire, that is the central local takeaway. The study names San Bernardino and Riverside among the areas that could be affected if a rupture propagates across both fault systems, placing the region inside the zone the authors say is most exposed to a large event.
The release also says the scenario could affect Los Angeles and the Coachella Valley, broadening the potential impact across a wide stretch of Southern California.
Burkhard’s team said the findings should inform seismic hazard assessments in an area where millions of people live and where major transportation, utility and other infrastructure cross or sit near active fault zones.
The study’s stress reconstruction compares present-day conditions with the past 1,000 years, a time span the authors used to judge how unusual current loading appears to be. The source material provided for this report did not include the paper’s full methods, uncertainty bounds or the exact model assumptions used in the reconstruction.
Even so, the authors said the result is a warning sign for the broader fault system rather than a prediction tied to any one date or place. Their main claim is that the San Andreas and San Jacinto systems have accumulated stress to levels that are unusually high on a millennium scale, with some segments at the top of the reconstructed range.
The university release quoted Burkhard again as saying, “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.”
That assessment gives the Inland Empire particular relevance because the study highlights Cajon Pass, San Bernardino and Riverside as part of the corridor where a large, through-going rupture could have serious consequences. The paper’s authors said the combined-fault scenario would be more damaging than a rupture on only one fault system.
The study does not remove uncertainty about when the next major earthquake will occur. What it does say, according to the authors, is that the present stress state along parts of the San Andreas and San Jacinto systems is already at an extreme level by historical comparison.
The Journal of Geophysical Research: Solid Earth publication places the findings in the scientific record, and the University of Hawaiʻi at Mānoa team said the results should be used as part of future seismic hazard planning for Southern California.
