December 25, 2016 Earthquake: Chile

A few buildings damaged at Quellon and fissures and landslides blocked the Pan American Highway between Chonchi and Castro. Felt (VII) at Castro and Puerto Montt; (VI) at Ancud, Calbuco, Cisnes, Dalcahue, Melimoyu, Melinka, Puerto Varas and Quellon; (V) at La Union, Maullin, Osorno, Puerto Aisen, Puerto Saavedra, Rio Bueno, Teodoro Schmidt, Tolten and Valdivia. Felt (V) at Bolson and (III) at San Carlos de Bariloche, Argentina. Felt widely in central and southern Chile and in western Argentina. A small tsunami with maximum amplitude of 8 cm was recorded at Puerto Melinka. Castro, Los Lagos, Chile - CDI: 7; Arauco, Bio Bio, Chile - CDI: 6; Ancud, Los Lagos, Chile - CDI: 5; Puerto Varas, Los Lagos, Chile - CDI: 5 ; Loncoche, Araucania, Chile - CDI: 5

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.

(above from reference #13456)

The U.S. Geological Survey said the magnitude 7.6 quake struck at 11:22 a.m. local time (9:22 a.m. EST; 1422 GMT) near the southern tip of Chiloe Island, about 25 miles (39 kilometers) south-southwest of Puerto Quello and at a depth of 22 miles (35 kilometers). The area, some 800 miles (1,300 kilometers) south of the capital of Santiago, is relatively sparsely populated. National emergency director Ricardo Toro told a news conference that some 4,000 people were evacuated for fear of a possible tsunami following the quake, but the alert was eased about 90 minutes after the temblor. "There is no information of loss of life," Toro said, though he said some highways were damaged. The local electric company reported that power was cut to about 22,000 customers. (reference #11751)