An international research team led by a researcher at the University of Bern has modeled 1,000 years of earthquake history along the San Andreas and San Jacinto faults in Southern California.
An international research team led by a researcher at the University of Bern has modeled 1,000 years of earthquake history along the San Andreas and San Jacinto faults in Southern California. The result: stresses in the crust are higher today than at any time in the last millennium – and a critical fault junction near Los Angeles could decide how big the next major earthquake will be.
Earthquakes usually occur along fracture zones in the Earth's crust, where large tectonic plates slide past one another and become locked. Stress builds up over long periods of time 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 the majority 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, which is 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 has 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. The results show that tectonic stresses in the region have reached and, in some cases, exceeded the highest levels of the last millennium. In the study, the researchers also introduce the concept of Cajon Pass as an "earthquake gate": a junction that controls whether large earthquakes remain confined to a single fault or propagate across both systems simultaneously. The study has just been published in Journal of Geophysical Research: Solid Earth.
Read More: University of Bern
