M 7.6 - 41 km SW of Quellón, Chile

Tectonic Summary

The December 25, 2016, M 7.6 earthquake occurred as the result of shallow thrust faulting in southern Chile. At the location of this earthquake, the oceanic Nazca plate converges with and subducts beneath the South America plate in an east-northeast direction, at a rate of approximately 73 mm/yr. The earthquake location, depth and shallow thrusting focal mechanism solution, all indicate this earthquake likely occurred on the subduction zone interface.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Thrust-faulting events of the size of the December 25, 2016, M 7.6 earthquake are typically about 90x45 km (length x width).

The Chilean subduction zone frequently hosts large earthquakes, and has hosted several M 8+ events this century, including the M 8.8 Maule earthquake in February 2010 approximately 850 km to the north of the December 25, 2016 earthquake (but which ruptured to within 650 km of today’s earthquake). The December 25 event is also within the ~1,000 km long rupture zone of the 1960 M 9.5 southern Chile earthquake, the largest event ever recorded in human history (about 1,000 times bigger than today’s earthquake). Over the preceding century, 6 other M 6.5+ earthquakes have occurred within 250 km of the December 25th earthquake. The 1960 M 9.5 earthquake and tsunami resulted in the loss 1,600 lives in Chile, and the tsunami took another 200 lives in Japan, Hawaii, and the Philippines. That event had several foreshocks over the preceding 36 hours, of M 8.1, M 7.1, and M 7.8.