California earthquake fears grow as San Andreas fault reaches historic stress levels

Southern California’s San Andreas and San Jacinto fault systems are experiencing their highest levels of tectonic stress in at least 1,000 years, according to a new scientific study.

Researchers from the University of Hawaii at Mānoa found that both fault systems are in what they describe as a “critically loaded state”, increasing concerns about the potential for a major earthquake in the future.

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“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,” lead author Liliane Burkhard said in a statement accompanying the study published in the Journal of Geophysical Research: Solid Earth.

The research highlights the importance of Cajon Pass, a key junction between the two fault systems.

Scientists say it could act as an “earthquake gate”, either limiting the spread of a rupture or allowing a major event to involve both faults simultaneously.

“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.

Using computer simulations and 1,000 years of earthquake data, researchers examined how stress builds and is released across the region.

The study does not predict when a major earthquake could occur. However, Burkhard said the findings provide a better understanding of the risks and possible earthquake scenarios that communities should prepare for.