The March 1, 2019, M 7.0 Peru earthquake near Lake Titicaca, occurred as the result of normal faulting at an intermediate depth, approximately 260 km beneath southeastern Peru within the lithosphere of the subducted Nazca plate. Focal mechanism solutions indicate that rupture occurred on either a steeply dipping normal fault striking westward, or on a shallowly dipping normal fault striking to the southeast. Slip on a fault of either orientation would accommodate the down-dip extension of the Nazca slab. At the location of the earthquake, the oceanic Nazca plate moves east-northeast relative to the South America plate at a rate of about 71 mm/yr, subducting at the Peru-Chile Trench west of the Peruvian coast and sinking into the mantle beneath South America. Like most western South America earthquakes, this event was caused by strains generated by the ongoing subduction process.
Earthquakes like this event, with focal depths between 70 and 300 km, are commonly termed intermediate-depth earthquakes. Intermediate-depth earthquakes represent deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. They typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters. Deep-focus earthquakes, those with focal depths greater than 300 km, also occur in the subducted Nazca plate farther east from the Peru-Chile Trench, beneath western Brazil and central Argentina. Earthquakes have been reliably located to depths of about 650 km in this region.
The Peru-Chile Trench is an area that hosts large earthquakes quite regularly. Within 500 km of the February 22nd earthquake, there have been 10 other intermediate depth earthquakes with magnitudes of 6.5+ over the preceding century. Today’s earthquake is the largest of these; another M 7.0 event occurred about 280 km to the northwest in July 1991, at a depth of about 100 km. That event caused some damage in Cuzco.
