Southern California\u2019s 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 \u201ccritically loaded state\u201d, according to a study published earlier this month.<\/p>\n
\u201cOur 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,\u201d Liliane Burkhard, the lead author of the study published<\/a> in the Journal of Geophysical Research: Solid Earth, said in a statement<\/a>.<\/p>\n Cajon Pass, which sits at the junction of the faults, could play a key role, acting as an \u201cearthquake gate\u201d 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 \u201chas continued to accumulate and is now at unprecedented levels\u201d, which has increased the chances of a large quake in the future.<\/p>\n \u201cThe conditions that determine whether the \u2018earthquake gate\u2019 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,\u201d said Burkhard.<\/p>\n \u201cRight 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.\u201d<\/p>\n The team of scientists at the University of Hawaii at M\u0101noa used a computer model to see how stress accumulates and releases in the fault systems and input 1,000 years of earthquake history to simulate how much stress is currently present. Their research found that Cajon Pass could \u201cfacilitate a joint rupture of both the San Andreas and San Jacinto faults simultaneously\u201d, and have impacts across southern California.<\/p>\n Their research does not predict when such a quake might happen, but is necessary to better understand the risks, Burkhard said.<\/p>\n \u201cWhat we can say is that the system is critically stressed, and that physics-based models like this one give us a clearer picture of the range of scenarios we should be prepared for.\u201d<\/p>\n