Overview
- Researchers examined more than 130 deep-sea sediment cores spanning roughly 3,000 years from off northern California.
- The peer-reviewed Geosphere paper identifies inverted, stacked turbidite layers consistent with two major earthquakes occurring minutes to decades apart.
- The record shows at least eight northern San Andreas earthquakes happened within decades of Cascadia ruptures, with the 1700 pairing possibly minutes to hours apart.
- The two systems are not perfectly synchronized, as evidenced by one-off events such as the 1906 San Francisco earthquake on the San Andreas.
- Scientists stress the findings do not forecast specific dates yet urge emergency planners to prepare for a compound Cascadia–San Andreas scenario.