Understanding the massive 7.0 Peru / Brazil earthquake (August 24 2011)

About : A massive – magnitude 7.0 -  luckily deep earthquake, struck Peru close to the Brazilian border. Due to its depth – 145.1 km (90.2 miles) – it was felt also in all neighboring countries.
Read also our main article "Massive deep earthquake shakes Peru near the Brazilian border – 20 injured"

Tectonic Summary

I Have Felt It map

The August 24, 2011 M 7.0 Peru earthquake occurred at a depth of approximately 150 km beneath the Earth's surface as a result of normal faulting within the subducting Nazca slab. The event struck near the boundary between the Nazca and South America plates, as the Nazca plate sinks towards the northeast beneath the South American continent.
At the location of this earthquake, the Nazca plate moves approximately east-northeast with respect to South America at a rate of 67 mm/yr.
The Nazca plate is seismically active northeast of the August 24 epicenter to depths of over 600 km; the stresses generating this earthquake may result from the bending of the plate as it transitions from a sub-horizontal region southwest of the epicenter to sink at steeper dips towards the mantle transition zone.

This section of the subducting Nazca plate has hosted several moderate earthquakes in the past, with 7 earthquakes of M 6 or greater in the past quarter century, though none have been as large as the August 24 event.
The most recent nearby earthquake was a M 6.4 shock just over 10 km to the east in August 2008.

Historic earthquakes map

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.

Text and images : USGS

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