Poster of the Maule, Chile Earthquake of 25 March 2012 - Magnitude 7.1

Tectonic Summary

The South American arc extends over 7,000 km, from the Chilean margin triple junction offshore of southern Chile to its intersection with the Panama fracture zone, offshore of the southern coast of Panama in Central America. It marks the plate boundary between the subducting Nazca plate and the South America plate, where the oceanic crust and lithosphere of the Nazca plate begin their descent into the mantle beneath South America. The convergence associated with this subduction process is responsible for the uplift of the Andes Mountains, and for the active volcanic chain present along much of this deformation front. Relative to a fixed South America plate, the Nazca plate moves slightly north of eastwards at a rate varying from approximately 80 mm/yr in the south to approximately 70 mm/yr in the north.

Subduction zones such as the South America arc are geologically complex and generate numerous earthquakes from a variety of tectonic processes that cause deformation of the western edge of South America. Crustal deformation and subsequent mountain building in the overriding South America plate generate shallow earthquakes. Slip along the dipping interface between the two plates generates frequent and often large interplate earthquakes between depths of approximately 10 to 60 km. Since 1900, numerous magnitude 8 or greater earthquakes have occurred on the interface between the Nazca and South America plates, including the 1960 M9.5 earthquake in southern Chile, the largest instrumentally recorded earthquake in the world and the 2010 M8.8 earthquake north of the 1960 quake. Earthquakes can also be generated to depths greater than 600 km from internal deformation of the subducting Nazca plate. Although the rate of subduction varies little along the entire subduction zone, there are complex changes in geologic processes along the subduction zone that dramatically influence volcanic activity, earthquake generation and occurrence. For example, an extended zone of crustal seismicity in central-northern Argentina highlights a well-known 'flat-slab' region of this subduction zone, where the Nazca plate moves horizontally for several hundred kilometers before continuing its descent into the mantle. This transition in slab structure is coincident with a marked break in the Andes volcanic chain.

Earthquake Report


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