Understanding the M 7.1 Ecuador earthquake

USGS Tectonic Summary for the M 7.1 Ecuador earthquake

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 earth’s 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 earth’s 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.

The above explanation can be seen very well on the map at right. More to the east means a deeper and deeper subducted Nazca plate.  Yellow line are the plate boundaries. The blue earthquake dots are the kind of earthquakes as today in Ecuador.

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2 Responses

  1. Estoy en la selva amazónica del Ecuador, se sintió fuerte y duro mucho tiempo, pero no fue tanto como para terremoto.
    I^m in the amazonic jungle in Ecuador. The earthquaque was not so big. Do not belive all the things on tv.

  2. This is because the depth was at nearly 200 km . If the same earthquake would occur at 20 km, human loss would be considerable.
    Esto se debe a la profundidad era de casi 200 km. Si el mismo terremoto que ocurriría en 20 km, pérdida de vidas humanas sería considerable.

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