Earthquake Ancestors

Layers of sand in the earth have helped seismologists investigate the history of earthquakes in Chile.

Photo by Pierre St. Amand Earthquake damage to homes in the town of Valdivia in Chile, near the epicenter of the earthquake.

In May of 1960, the largest earthquake ever recorded rocked an idyllic seascape on the coast of Chile. Hundreds of locals, frightened by the violent shaking of the land, sought refuge in small boats. They thought they were safe - until the sea roared with the 75-foot waves of the quake’s daughter tsunami. And they weren’t the only ones who felt it – giant waves were triggered in Japan and Hawaii, killing people and destroying homes.

Typically, the magnitude of an earthquake increases with the number of years since the last one in the area. So considering its enormity, at least 350 years should have elapsed between the Chilean quake and its immediate predecessor. Sure enough, Spanish conquistadors wrote of a large quake in 1575. But here’s the big mystery: other documents suggest the 1575 quake wasn’t the last one before 1960. Two others are documented: one in 1737 and another in 1837. This left those who were studying the 1960 event scratching their heads to figure out how so much energy could have built up in just 123 years.

Four decades later, a team of international seismologists, led by Brian Atwater from the University of Washington and Marco Cisternas from the Pontificia Universidad Católica de Valparaíso in Chile, have finally examined the tracks of the Chilean giant and the devastating tsunami it caused. As revealed last September in Nature, their analysis of the layers of earth in the coastal region has shed light upon the long-misunderstood history of the disaster.