A new study on Earthquake In California says the San Andreas and San Jacinto faults are under more stress than at any point in the last 1,000 years. The researchers say that makes another major earthquake in Southern California a matter of when, not whether, even if no one can pin down the timing.
Kate Scharer, a geologist with the U.S. Geological Survey and a co-author of the study, said, "Because it’s been quite a long time since the Southern San Andreas or the San Jacinto have had a large earthquake, we’ve accumulated a lot of stress." The study says that stress has been building gradually since the last Big One in 1857.
Burkhard on Cajon Pass
The team estimated current stress levels from geological evidence, including tree-ring records and sediment samples, then used a computer model to track how pressure accumulates along faults over time. Harold Tobin, director of the Pacific Northwest Seismic Network and a professor at the University of Washington, said, "This [study] puts it on more of a quantitative, rigorous scientific basis."
Liliane Burkhard, the study’s lead author and a research affiliate in the Hawaiʻi Institute of Geophysics and Planetology, said, "Cajon Pass could act as an ‘earthquake gate,’ like a junction that either stops or transmits large ruptures between the San Andreas and San Jacinto faults depending on stress conditions." She said a major rupture could jump from one fault system to another there, sending shaking farther across Southern California.
Southern California fault system
The study places that risk in a region that includes parts of some of the most densely populated areas in the country. Ahmed Elbanna of USC said, "This study was a great reminder that in Southern California, where we have parts of the most densely populated regions in the country, we are living on a multi-strand fault system," and the study says a rupture could affect millions more people across the Coachella Valley and San Bernardino County.
Scientists agree that Southern California will experience another major earthquake, but no one knows exactly when it will happen. The study’s practical message is to treat the faults as loaded now, not at some distant point in the future, and to keep emergency supplies ready for at least 72 hours of food, water and medications.
