Valdivia 1960: M9.5, Still the Strongest Quake Ever

The 1960 Valdivia earthquake, also called the Great Chilean earthquake, struck southern Chile on 22 May 1960 with a moment magnitude of 9.5 — the most powerful earthquake ever recorded by instruments.

The rupture ran roughly 800 km along the boundary where the Nazca Plate dives beneath the South American Plate. It triggered a Pacific-wide tsunami that killed people as far away as Hawaii, Japan and the Philippines, and it set off the eruption of the Cordón Caulle volcano days later.

Estimates of the death toll range widely, from about 1,655 to several thousand, with around two million people left homeless. Because so much of the energy was released offshore, the tsunami — not the shaking alone — caused a large share of the destruction. Valdivia remains the benchmark against which every other great earthquake is measured.

NOAA's historical tsunami database shows just how far that energy travelled: the wave reached Hilo, Hawaii in under 15 hours with a run-up near 10 metres, killing 61 people, then struck Japan around a day later — some 17,000 km from the epicentre — killing more than 100 more. It is one of the clearest demonstrations that a mega-thrust earthquake's danger is not confined to its own coastline.

USGS lists the mainshock hypocentral depth at about 25 km and notes it was preceded by a swarm of large foreshocks, including a M7.9 event on 21 May that had already devastated the Concepción area a day earlier. In the following months, seismic networks catalogued 318 aftershocks above magnitude 2, five of them at M7.0 or greater through November 1960 — an aftershock sequence long enough that some Chilean towns spent months rebuilding under repeated strong shaking. Roughly 47 hours after the mainshock, the Cordón Caulle volcanic complex erupted explosively for the first time in nearly 40 years, sending an ash column about 8 km high — a textbook case of a mega-earthquake triggering nearby volcanism through crustal stress transfer.