Cascadia and San Andreas faults may rupture back to back

A study of deep-sea sediment cores suggests the Cascadia subduction zone and the San Andreas fault can rupture in sync, with one major earthquake following the other within minutes to hours. Three such closely spaced events were identified over the past 1,500 years, the most recent around 1700.

• Sediment cores covering about 3,100 years of geologic history were analyzed
• Three cases of closely spaced Cascadia and northern San Andreas ruptures found in 1,500 years
• The most recent paired rupture occurred around 1700
• Only one similar case was previously observed, in Sumatra in 2004–2005