SAN BERNARDINO, Calif., June 24 (Inland Empire News Online) — 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, according to a peer-reviewed study led by University of Hawaiʻi at Mānoa scientists.
The study, published in the Journal of Geophysical Research: Solid Earth, is centered on a 1,000-year stress reconstruction for the fault systems that run through parts of inland Southern California. The researchers said the findings have direct implications for seismic hazard assessments in a densely populated corridor that includes the Inland Empire.
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, said the study shows stress levels on multiple fault segments are now at or above the highest values seen in the past millennium.
The University of Hawaiʻi release said the researchers described the system as critically loaded, with more than 160 years elapsed since the last major rupture. The release did not identify that rupture by name.
According to the study, modeled stress reached 3.6 megapascals on the San Jacinto-Bernardino section, the highest value seen anywhere in the 1,000-year simulation, and 2.8 megapascals on the neighboring Mojave South section of the San Andreas Fault.
The authors said Cajon Pass could help a joint rupture of the San Andreas and San Jacinto faults occur at the same time. They said such a through-going rupture could be significantly more damaging than a single-fault event.
The study said that scenario would affect densely populated areas including Los Angeles, San Bernardino, Riverside and the Coachella Valley. That puts the work in sharp focus for the Inland Empire, where San Bernardino County sits near the fault systems highlighted in the paper.
Burkhard said the results show the region may be capable of a large through-going rupture involving both fault systems. The study did not say when such an event might happen.
The research team said the findings matter for hazard planning across Southern California, where major transportation routes, cities and other infrastructure lie close to the fault systems studied.
