Research conducted by Earth scientists at the University of Hawaiʻi at Mānoa indicates that tectonic stress along Southern California’s San Andreas and San Jacinto fault systems has reached, and in some areas exceeded, the highest levels observed in the past 1,000 years. The study, published in the Journal of Geophysical Research: Solid Earth, notes that while the system is not currently showing signs of an imminent rupture, it is under unusually high stress as part of a long-term seismic cycle that could lead to large earthquakes, including multi-fault events.
Lead author Liliane Burkhard, a research affiliate at the University of Hawaiʻi’s Institute of Geophysics and Planetology, stated that the system has been highly stressed for over 160 years since the last major rupture. The research highlights Cajon Pass as a critical area that may influence the behavior of ruptures between the two fault systems.
The study suggests that a rupture involving both fault systems could result in more significant damage than a single-fault earthquake due to its size and proximity to major population centers such as Los Angeles, San Bernardino, Riverside, and the Coachella Valley.
The San Andreas Fault is characterized as a strike-slip plate boundary, where the Pacific Plate and North American Plate slide past each other horizontally. This means that in the event of a large earthquake, the movement is lateral rather than a separation of landmass.
The research also discusses the nature of surface rupture, which occurs when fault movement breaks through to the surface, potentially causing significant damage to infrastructure, particularly in areas built on soft or water-saturated soils.
California's location along the boundary of the Pacific and North American tectonic plates, along with its numerous active faults, contributes to its status as one of the most earthquake-prone regions in the United States.