Cascadia and San Andreas Faults Could Strike Back‑to‑Back, Study Finds

Scientists have found evidence that the Cascadia subduction zone and the northern San Andreas fault can rupture in rapid succession. Analysis of 3,100 years of ocean sediment layers revealed unusual deposits that indicate earthquakes on the two fault systems have occurred just minutes to hours apart, including the massive Cascadia event of 1700 CE.

The study identified these sedimentary signatures as markers of closely timed seismic activity, suggesting that the two major West Coast faults can synchronize their ruptures. If such a pattern were to repeat, the resulting earthquakes could strike major West Coast cities almost simultaneously, creating overlapping emergencies.

These findings show that the Cascadia subduction zone and northern San Andreas fault may strike back to back, and if this synchronization occurs again, several major West Coast cities could face emergencies at nearly the same time.