Poster of the Ecuador Earthquake of 12 August 2010 - Magnitude 7.1
This major earthquake occurred within the lithosphere of the Nazca plate. The earthquakes of Ecuador and most of western South America are due to strains generated by ongoing subduction of the Nazca plate beneath the South America plate. At the latitude of the earthquake, the oceanic Nazca plate moves east relative to the South America plate at a rate of about 7 cm per year. It is overridden by the South America plate at the Peru-Chile trench, west of the Ecuadoran coast, and sinks into the earths mantle beneath the South America plate. The subducted Nazca plate is seismically active to depths of about 650 km. This earthquake occurred as normal faulting within a segment of the subducted plate that has produced frequent earthquakes with focal depths of 160 km to 200 km beneath the earths surface. A magnitude 6.7 earthquake in 1971 was situated 60 km to the southwest of the August 12, 2010, earthquake at a depth of 170 km.
Earthquakes that have focal-depths between 70 and 300 km are commonly termed intermediate-depth earthquakes, as distinguished from shallow-focus earthquakes, having depths less than 70 km, and deep-focus earthquakes, having depths greater than 300 km. Intermediate-depth and deep-focus earthquakes represent deformation within subducted plates, rather than deformation at plate boundaries. Intermediate-depth and deep-focus earthquakes typically cause less damage on the ground surface above their foci than is the case with similar magnitude shallow-focus earthquakes, but large intermediate-depth and deep-focus earthquakes may be felt at great distances from their epicenters.
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