The 8.8 magnitude temblor that devastated Chile two weeks ago was a “megathrust”, scientists say. Megathrust quakes occur when tectonic plates along the fault lines are forced under one another, a movement called subduction. The Chile quake occurred when the Nazca plate in the eastern Pacific Ocean basin collided with the South American plate, releasing 50 gigatons of energy and disrupting 250 miles of ground along the fault line. The earthquake was so powerful that it moved the earth three inches off its axis, shortening the day by 1.26 microseconds.

The largest earthquake on record also took place in Chile fifty years ago, a 9.5 magnitude megathrust whose epicenter was 140 miles to the north of the February quake. The 1960 quake destroyed countless millions of dollars in property and killed 1,600; two hundred more died in Japan and the Philippines in the resulting tsunami. In the aftermath of the 1960 quake, Chile adopted building standards designed to minimize death and destruction in future seismic events.

Nevertheless, protecting against megathrusts is far from foolproof and significant damage will always result even with the strictest of structural codes. Hundreds died in the February Chile quake, and millions more were displaced while damages to insured property were estimated in the range of eight billion dollars.