U.S. News

Southern California’s San Andreas and San Jacinto fault systems are at their highest levels of tectonic stress in 1,000 years in what scientists describe as a “critically loaded state”, according to a study published earlier this month.

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

Cajon Pass, which sits at the junction of the faults, could play a key role, acting as an “earthquake gate” that can block large ruptures from traveling between the faults or involve both systems in one event, according to the research. It has been more than a century since the last major event, and stress “has continued to accumulate and is now at unprecedented levels”, which has increased the chances of a large quake in the future.

“The conditions that determine whether the ‘earthquake gate’ at Cajon Pass opens or stays closed appear to be related to how closely the stress levels on the two fault systems are aligned with each other at the time of rupture,” said Burkhard.