Then, fortuitously, one of Atwater's dead trees fell over. The rings of its roots allowed Yamaguchi to improve his estimate. The trees had met their demise during or just before the spring of 1700. With more modelling and studies of other tsunami-generating quakes, Satake fixed the time of the great Cascadia earthquake at dia9 pm on 26 January 1700. The magnitude has been harder to pin down.
Scientists seem to be favouring the higher figure.
That could be bad news for Northwesterners. To have New Scientist delivered to your door, visit our subscription pages . Please include the magazine issue number and date with your order.