A Chilean surprise

摘要

Initiation of the great 2010 Chile earthquake occurred within the rupture zone of the 1835 event experienced by Charles Darwin. However, the peak fault slip was to the north of the epicentre - not where it was expected to occur. On 20 February 1835, Charles Darwin was resting in the woods near Valdivia, Chile, when the ground suddenly trembled for about two minutes, although "the time appeared much longer"1. Two weeks later, at Conception, Darwin saw the devastation wrought by the ground shaking and tsunami, and observed coastal uplift that he inferred to have "accompanied or caused the earthquake"1. This great earthquake, with an estimated2 seismic magnitude (Mw) of about 8.5, is now understood to have occurred on a megathrust fault, where the Nazca plate underthrusts the South American plate with a plate-convergence rate of about 70 millimetres per year.