The April 1, 2014 M 8.2 earthquake in northern Chile occurred as the result of thrust faulting at shallow depths near the Chilean coast. The location and mechanism of the earthquake are consistent with slipping on the primary plate boundary interface, or megathrust, between the Nazca and South America plates. At the latitude of the earthquake, the Nazca plate subducts eastward beneath the South America plate at the rate of 65 mm/yr. Subduction along the Peru-Chile Trench to the west of Chile has led to the uplift of the Andes mountain range and has produced some of the largest earthquakes in the world, including the 2010 M 8.8 Maule earthquake in central Chile, and the largest earthquake on the record, the 1960 M 9.5 earthquake in southern Chile.
The April 1 earthquake occurred in a region of historic seismic quiescence - termed the northern Chile or Iquique seismic gap. Historical records indicate a M 8.8 earthquake occurred within the Iquique gap in 1877, which was preceded immediately to the north by an M 8.8 earthquake in 1868. A recent increase in seismicity rates has occurred in the vicinity of the April 1 earthquake. An M 6.7 earthquake with similar faulting mechanism occurred on March 16, 2014, whcich was followed by 60+ earthquake of M4+, and 26 earthquakes of M5+. The March 16 earthquake was also followed by three M 6.2 events on March 17, March 22, and March 23, respectively. The spatial distribution of seismicity following the March 16 event migrated spatially to the north through time, starting near 20oS and moving to 19.5oS.
The initial location of the April 1 earthquake places the event near the northern end of this seismic sequence. Other recent large plate boundary ruptures bound the possible rupture area of the April 1 event, 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. Other nearby events along the plate boundary interface include an M 7.4 in 1967 as well as an M 7.7 in 2005 in the deeper portion of the subduction zone beneath inland Chile. On April 3, 2014 a M 7.6 aftershock off the west coast of northern Chile occurred as a result of thrust motion at the depth of approximately 40 km, 23 km south of the city Iquique. The location and mechanism of the earthquake are consistent with slipping on the plate boundary interface, or megathrust, between the Nazca and South America plates. At the latitude of the event, the Nazca plate is subducting beneath South America at the rate of 73 mm/yr.
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