The 2011 Contamana Earthquake: Seismic Activity in Eastern Peru

On 24 August 2011 at 17:46 local time, a magnitude 7.0 earthquake occurred 64 km east-southeast of Contamana, Peru, at a focal depth of 147 km. The event is recorded as the sole strong earthquake (M 7.0 or greater) in the region since 1 January 2000. Its substantial depth places the hypocenter within the subducting oceanic slab rather than at the plate interface, resulting in relatively limited surface damage despite the magnitude. Contamana lies within the Ucayali Basin of eastern Peru, part of the Andean foreland where the Nazca Plate subducts beneath the South American Plate at a rate of approximately 6–7 cm per year. The basin is underlain by thick sedimentary sequences deposited over Precambrian basement of the Amazonian craton. Intermediate-depth seismicity, such as the 2011 event, arises from dehydration embrittlement and phase transitions within the descending slab, which can generate earthquakes down to 150–200 km. The broader geological history of the region reflects ongoing Andean orogeny that began in the Cretaceous and intensified during the Miocene. Compressional tectonics have produced east-vergent thrust systems along the Andean front, while the foreland basin has accumulated several kilometers of Cenozoic sediment derived from Andean erosion. Although surface faulting is minimal in the Amazonian lowlands, the deep subduction zone remains the primary source of regional seismicity. Post-2011 monitoring by regional seismic networks has confirmed continued low-to-moderate activity at intermediate depths beneath the Ucayali Basin, consistent with the persistent subduction regime. No comparable magnitude 7.0 events have been recorded in the immediate vicinity since the 2011 shock.

References

USGS Earthquake Catalog (event page for 2011-08-24 M 7.0 Peru)
Global CMT Catalog
Instituto Geofísico del Perú regional seismicity reports