M 8.2 - 93 km NW of Iquique, Chile

Tectonic Summary

The April 1, 2014, M 8.2 earthquake off the west coast of northern Chile occurred as the result of thrust faulting at shallow depths near the Chilean coast. At the location of the earthquake, the Nazca plate subducts eastward beneath the South America plate at a velocity of 72 mm/yr. The location and mechanism of the earthquake are consistent with slip on the primary plate boundary interface, or megathrust, between these two major plates. Subduction along the Peru-Chile Trench to the west of Chile has led to uplift of the Andes Mountain Range and has produced some of the largest earthquakes in the world, including the damaging 2010 M 8.8 Maule earthquake in central Chile, and the largest earthquake on record, the 1960 M 9.5 earthquake in southern Chile.

The April 1st earthquake occurred in a region of historic seismic quiescence, which is termed the northern Chile or Iquique seismic gap. Historical records indicate that an earthquake of about M 8.8 occurred within the Iquique gap in 1877, which was preceded immediately to the north by an earthquake of about M 8.8 in 1868.

A recent increase in seismicity rates has occurred in the vicinity of the April 1st earthquake. A M 6.7 earthquake with similar faulting mechanism occurred on March 16, 2014, and was followed by more than 60 earthquakes of M 4+ and 26 earthquakes of M 5+. The March 16th earthquake was also followed by three M 6.2 events on March 17, March 22, and March 23. The spatial distribution of seismicity following the March 16th event migrated spatially to the north through time, starting near 20 degrees south and moving to about 19.5 degrees south. The initial location of the April 1st earthquake places the event near the northern end of this seismic sequence.

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 April 1, 2014, earthquake are typically about 200x80 km (length x width); modeling of this earthquake implies dimensions of about 80x80 km, predominantly down-dip of the hypocenter. This indicates there is a substantial section of the seismic gap that remains unruptured.

Other recent large plate boundary ruptures bound the seismic gap in which the April 1st event occurred, including the 2001 M 8.4 Peru earthquake adjacent to the south coast of Peru to the north and the 2007 M 7.7 Tocopilla, Chile, and 1995 M 8.1 Antofagasta, Chile, earthquakes to the south, all of which had many associated fatalities and damages. Other nearby events along the plate boundary interface include a M 7.4 earthquake in 1967 as well as a M 7.7 earthquake in 2005 in the deeper portion of the subduction zone beneath inland Chile.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)