Magnitude 8 Peru Earthquake of August 15, 2007
The Peru earthquake resulted from the sudden release of strain that had accumulated due to subduction of the Nazca plate beneath the South American plate. The two plates are converging at a rate of 77 mm per year. The earthquake occurred as thrust-faulting on the interface between the two plates, where the Nazca plate moves toward the South American plate in a northeasterly direction and dives beneath the South American plate at the Peru – Chile Trench. The map below shows the directions and rates of motion of surrounding plates with respect to the South American Plate.
Coastal Peru has a history of very large earthquakes. The August 15 shock originated just south of the source region of the magnitude 8.1 earthquake of October, 1974, and just north of the source regions of major earthquakes that occurred in August, 1942 (magnitude 7.7) and 1996 (magnitude 7.7). The largest coastal Peru earthquake of the last two centuries was the magnitude 9 earthquake of 1868, which was centered about 700 km southeast of the August 15 earthquake. The 1868 shock produced a tsunami that killed several thousand people along the South American coast and also caused damage in Hawaii.
The largest instrumentally recorded earthquake recorded to date also occurred between the Nazca and South American plates, but farther south along the coast of Chile. This was the M 9.5 Chile earthquake of 1960, which ruptured 1,000 km of the plate boundary.
Red Star is epicenter of the Peru event. The modeled rupture is 225 km long by 80 km wide. The colors within this region represent the surface projection of the slip or displacement, measured in centimeters. Maximum slip reached 8 meters in one area. This is an impressive amount of displacement in a single earthquake but is much less than the maximum 20 meter displacement that occurred during the December 2004 M 9.2 Sumatra – Andaman Islands earthquake in the eastern Indian Ocean. The black line indicates the major plate boundary between the Nazca and South American tectonic plates. Reference: http://earthquake.usgs.gov/eqcenter/eqinthenews/2007/us2007gbcv/finite_fault.php
Seismograms from the Peru earthquake
2007/08/15 23:40:57 -13.354 –76.509 39km Mw 8
John Lahr’s station in Corvallis, Oregon, at 71.8 degrees.
Bob Butler’s station at the University of Portland, Oregon, at 72 degrees.
Alan Jones’ station in Binghamton, New York, at 55.45 degrees.