Earthquakes usually occur along fracture zones in Earth’s crust, where large tectonic plates slide past one another and become locked. Stress builds up over long periods and is suddenly released in the form of an earthquake. In Southern California, the San Andreas and San Jacinto faults are among the most significant of these zones, accommodating most of the plate motion in the region.
Where the two fault systems approach each other northeast of Los Angeles lies the Cajon Pass—a tectonically complex junction where a rupture on one fault could potentially cross onto the other. Since the last major earthquake to affect the wider Los Angeles region, the Fort Tejon earthquake of 1857, with a magnitude of 7.9, tectonic stress along the fault segments has built up continuously during a prolonged quiet period that has long concerned researchers, given the potential for a large future rupture.
In a new study led by Dr. Liliane Burkhard of the Division of Space Research and Planetary Sciences (WP) at the Physics Institute of the University of Bern, an international research team modeled 1,000 years of earthquake history along the southern San Andreas and San Jacinto fault systems to estimate the present-day stress loading at Cajon Pass. Researchers from the University of Hawaiʻi at Mānoa, the U.S. Geological Survey Earthquake Science Center in Pasadena, and the Scripps Institution of Oceanography at UC San Diego were involved…