Cascadia and San Andreas: Evidence Suggests Sequential Earthquake Risk

The Cascadia subduction zone and northern San Andreas fault may sometimes rupture in rapid succession, according to evidence preserved in 3,100 years of ocean sediments. Researchers identified unusual sediment layers suggesting that earthquakes on the two systems have occurred just minutes to hours apart, including around the massive Cascadia earthquake of 1700. If such synchronization happened again, several major West Coast cities could face emergencies at nearly the same time.