The last megathrust earthquake at the Cascadia subduction zone was the 1700 Cascadia earthquake , estimated to have a moment magnitude of 8.7 to 9.2 . Based on carbon dating of local tsunami deposits , it is inferred to have occurred around 1700 . Evidence of this earthquake is also seen in the ghost forest along the bank of the Copalis River in Washington . The rings of the dead trees indicate that they died around 1700 , and it is believed that they were killed when the earthquake occurred and sank the ground beneath them causing the trees to be flooded by saltwater . Japanese records indicate that a tsunami occurred in Japan on 26 January 1700 , which was likely caused by this earthquake
1700 Cascadia earthquake
1700 Cascadia earthquake
Juan de Fuca Plate