Seismic History and Geology of Southern Peru's Coastal Region

Southern Peru lies along the active subduction zone where the Nazca Plate descends beneath the South American Plate at rates of approximately 6–7 cm per year. This tectonic setting produces frequent large-magnitude earthquakes, with hypocenters commonly occurring at depths of 20–40 km. The coastal area near Atico and Atiquipa experiences elevated seismic hazard due to the locked portion of the plate interface, which periodically releases accumulated strain in megathrust events. On 23 June 2001 at 20:33 UTC, a moment magnitude 8.4 earthquake struck 6 km SSW of Atico at a focal depth of 33 km. The event ruptured a substantial segment of the plate boundary, generating strong ground shaking across southern Peru and triggering a tsunami that affected local coastal communities. This earthquake ranks among the largest instrumentally recorded in the region during the modern era. Seismic activity has continued since 2000. A magnitude 7.2 earthquake occurred on 28 June 2024, located 10 km WSW of Atiquipa and approximately 99 km from the 2001 rupture zone. This event further illustrates the ongoing release of stress along adjacent fault segments. Geological records indicate that the Peru-Chile Trench has hosted multiple great earthquakes over the past century, including events in 1940, 1974, and 2007. These quakes share similar characteristics: shallow thrust mechanisms, significant coastal uplift or subsidence, and aftershock sequences lasting weeks to months. The 2001 mainshock was followed by a robust aftershock sequence that included several events above magnitude 6.0. The regional geology features the Andean orogen, with coastal plains underlain by accreted marine sediments and volcanic arcs farther inland. Soil amplification in river valleys and soft sediments near Atico can intensify shaking during large events, increasing vulnerability for nearby populations. Ongoing monitoring by regional seismic networks provides real-time data essential for hazard assessment. Updated catalogs confirm that the area remains capable of producing magnitude 8+ earthquakes, underscoring the importance of preparedness measures such as building codes and tsunami evacuation planning.

References

USGS Earthquake Catalog Global CMT Project Peru Instituto Geofísico del Perú seismic reports