Stress levels along the San Andreas and San Jacinto fault lines in Southern California have reached their highest point in over a millennium, raising concerns about seismic risk in one of the most densely populated regions in the United States.
According to a new study published in the Journal of Geophysical Research: Solid Earth, the region may be capable of a large through-going rupture involving both fault systems, which could be significantly more damaging than a single-fault event.
The study used a physics-based computer model to simulate how stress builds up and gets released along the fault systems, including at a critical junction between the two known as Cajon Pass.
Researchers found that 36 earthquakes with magnitudes of 6.4 or higher have hit the Los Angeles region over the past 1,000 years, and today, about 13 million people live in the area.
Lead author Liliane Burkhard said, 'Right 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.'
The study also found that Cajon Pass could act as an 'earthquake gate,' sometimes blocking large ruptures from crossing between the two fault systems and sometimes allowing them to pass through.
Researchers believe the findings will help improve seismic hazard assessments, emergency preparedness, and infrastructure planning.
