Deep-Focus Seismicity Near Iñapari, Peru

The Peruvian region surrounding Iñapari lies within the Amazonian foreland basin, east of the Andean orogen. This area forms part of the South American plate, where the Nazca plate continues to subduct eastward beneath the continent. Subduction occurs at an average rate of approximately 6–7 cm per year along the Peru-Chile Trench. The geometry of the subducting slab allows hypocenters to reach depths exceeding 600 km beneath the eastern lowlands, producing deep-focus earthquakes that are felt across wide areas yet rarely cause surface damage. On 24 August 2018 at 09:04 UTC, a magnitude 7.1 earthquake occurred 136 km west of Iñapari at a focal depth of 630 km. The event originated within the cold, brittle interior of the subducted Nazca slab. A comparable magnitude 7.6 earthquake struck 155 km west-northwest of Iñapari on 24 November 2015, with its epicenter located 56 km from the 2018 rupture. Both events illustrate the persistent seismic activity along the deeper segments of the slab. Deep earthquakes in this setting result from phase transitions and thermal stresses within the descending oceanic lithosphere rather than from brittle failure at shallow crustal levels. Historical records document similar large events in the region throughout the instrumental era, confirming that the slab remains seismically active to great depths. Because of their depth, these earthquakes produce minimal aftershock sequences and limited ground deformation at the surface. The broader geological history of the area reflects the ongoing construction of the Andes since the Mesozoic, with accelerated uplift during the Cenozoic driven by continued plate convergence. The foreland basin east of the Andes records sediment derived from the rising cordillera, while the underlying basement belongs to the stable Amazonian craton. Modern instrumentation, including broadband seismometers operated by regional networks, continues to monitor slab seismicity and refine models of subduction dynamics beneath eastern Peru. References
USGS Earthquake Catalog (event parameters for 24 Aug 2018 and 24 Nov 2015)
Global CMT Project (focal mechanisms and depths)
Peru’s Instituto Geofísico del Perú (regional seismicity summaries)