- © 2012 by the Seismological Society of America
The seismic activity in Peru has its origin in the convergence process between the Nazca and the South American plates. Such convergence takes place at an average velocity on the order of 7–8 cm/yr (DeMets et al., 1980; Norabuena et al., 1999). This process is responsible for the largest damaging shallow interplate underthrusting earthquakes, the intraplate plate events in the downgoing Nazca slab, and the shallow intraplate crustal events in the overriding South American plate. The interplate events, representing slip between the plates, are the largest earthquakes and can cause considerable damage along the coast from both ground shaking and tsunamis. Shallow crustal earthquakes, although not as large as the underthrusting events, in near‐population centers can be damaging over small regions. Large intraplate earthquakes in the slab are not as common but can be a source of damage and concern especially if they are large. The recent 24 August 2011 earthquake is one of these intraplate events in the slab at ∼150 km in depth that was well recorded in Peru and worldwide. Many of the large historic intermediate‐depth slab earthquakes have not been well recorded with modern seismic or strong ground‐motion instruments. Yet, they represent a significant hazard in the high cordillera region of Peru.
Peru has a long and continuous history of earthquakes. Every year, an average of 150 earthquakes are recorded and reported, with intensities of II–III [modified Mercalli (MM) scale] and magnitudes ML≥4.0. Underthrusting earthquakes of larger magnitudes (Mw≥7.0) are less frequent but can cause significant damage over large areas, such as the event that occurred in the Pisco region on 24 August 2007 (Mw 7.9; Tavera and Bernal, 2008; Perfettini et al., 2010). The earthquakes in the overriding plate causing crustal deformation at shallow depths are less …