The January 14, 2018, M 7.1 earthquake offshore southern Peru occurred as the result of shallow thrust faulting on or near the boundary between the South America plate and the subducting Nazca plate. The Nazca plate subducts beneath the South America plate at the Peru-Chile Trench offshore of western South America, 80 km to the southwest of today’s earthquake, and dips east-northeast beneath the South American continent. At the location of the January 14, 2018 earthquake, the Nazca plate moves to the east-northeast with respect to the South America plate at a velocity of about 70 mm/yr. The location, depth and focal mechanism solution of today’s earthquake are consistent with it occurring on the megathrust interface between the two plates.
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 January 14, 2018 earthquake are typically about 50x25 km (length x width).
The plate boundary region between the Nazca and South America plates experiences a large number of earthquakes. The region within 250 km of the epicenter of the January 14 earthquake has experienced 13 previous earthquakes of M 6.5+ over the preceding century. The largest of these, the M 8.4 earthquake of June 23, 2001, occurred along the plate boundary 130 km to the southeast (and ruptured from there ~ 200 km to the southeast). It resulted in at least 74 fatalities and destroyed more than 17,000 homes. The epicenter of the M 7.7 earthquake of November 12, 1996, is about 130 km to the northwest of today’s earthquake. That event ruptured much of the megathrust between its epicenter and the epicenter of the January 14, 2018 earthquake, and resulted in at least 14 fatalities and left 12,000 people homeless. The September 25, 2013, M 7.1 earthquake, just 25 km to the southeast of today’s event, is not known to have caused any fatalities.