SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — A University of Hawaiʻi at Mānoa-led study published in the peer-reviewed Journal of Geophysical Research: Solid Earth 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 a 1,000-year reconstruction.
The authors say the finding matters for earthquake hazard in a corridor that includes the Inland Empire and other densely populated parts of Southern California. The study, led by earth scientists at the University of Hawaiʻi at Mānoa, says the fault system is now in a critically loaded state after more than 160 years since the last major rupture.
Lead author Liliane Burkhard, identified in the university’s release 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 a scientist at the University of Bern in Switzerland, said the results show stress levels on multiple fault segments are now at or above the highest values seen in the past millennium.
“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 university release.
The study focuses on the San Andreas and San Jacinto fault systems, two major earthquake sources in Southern California. In the university’s summary of the work, the authors said their results point to the possibility of a large through-going rupture involving both fault systems.
That type of event could be more damaging than a rupture on a single fault, the release said, and could affect Los Angeles, San Bernardino, Riverside and the Coachella Valley.
The study also identifies Cajon Pass as a location that could help allow a joint rupture of the two faults. The university release said that connection could make the region more vulnerable to a larger quake than would be expected from either fault alone.
The research was published in a journal that uses peer review, but the source material provided for the study does not include the full paper text, the authors’ detailed methods or the study’s uncertainty bounds. The release and a summary from Phys.org say the finding comes from a 1,000-year stress reconstruction, but the supplied material does not provide enough detail to independently assess every modeling assumption.
Phys.org reported that the modeled stress reached 3.6 megapascals on the San Jacinto-Bernardino section, exceeding the highest value seen anywhere in the 1,000-year simulation. It also reported 2.8 megapascals on the neighboring Mojave South section of the San Andreas Fault.
The provided material does not clarify whether those values are direct measurements or modeled estimates, though the Phys.org summary describes them as modeled stress. It also does not provide a margin of error or confidence interval for the claim that present-day stress has matched or surpassed the highest level in the past 1,000 years.
The university release says the work has direct implications for seismic hazard assessments in a heavily populated and infrastructure-critical part of the United States. The release does not name a government agency that oversees those assessments, and it does not claim the study can predict the timing of a future earthquake.
That distinction matters. The study describes stress conditions and fault behavior, not a forecast of when the next major rupture will happen.
Southern California has long been one of the most closely watched earthquake regions in the country because the San Andreas fault system marks the boundary between the Pacific and North American plates. The San Jacinto fault system runs through parts of inland Southern California and has been identified in the study as part of a broader rupture system with the San Andreas.
The university said the region’s present loading is especially important because the fault network has gone more than 160 years since its last major rupture. The source material does not identify that rupture by name, date or location.
Still, the researchers say the combination of time since the last major rupture and the high stress levels now seen across the fault system points to elevated concern for a larger earthquake sequence. In the university release, Burkhard said the study indicates the region may be capable of a large rupture involving both fault systems.
The university’s summary frames the work as relevant not only for scientists but also for hazard planners in Southern California. The release says a joint rupture across the San Andreas and San Jacinto systems would be significantly more damaging than a single-fault event.
The Inland Empire is central to that risk picture because the study and its summary specifically name San Bernardino, Riverside and Cajon Pass. Those places sit near the fault systems or along corridors that could be affected by strong shaking from a large event.
The university release also names Los Angeles and the Coachella Valley as areas that could be affected by such a rupture. The supplied source material does not quantify expected damage, shaking intensity or casualties.
What the study does establish, according to the university and the journal publication, is that stress levels along key parts of the Southern California fault network are now at an extreme point in the 1,000-year record used by the researchers. The authors say that makes the present-day fault system a critical one to watch.
The article in Journal of Geophysical Research: Solid Earth is the primary source for the findings described in the university release. A Phys.org summary, published June 8, 2026, adds section-specific stress values from the study. The University of Hawaiʻi at Mānoa release was published June 10 and updated June 16.
The source material provided for this report does not include the exact publication date of the journal article or its DOI. It also does not include the full list of co-authors, the number of studies or datasets used in the modeling, or whether independent groups have replicated the same stress reconstruction.
Even so, the central claim is clear in the sources provided: the San Andreas and San Jacinto fault systems in Southern California are now, by the researchers’ account, at or above the highest stress levels seen in the last 1,000 years, with the Inland Empire among the regions most directly tied to the risk picture described in the study.
