[2] The presence of active subduction produces large earthquakes when elastic energy along the plate boundary (megathrust) is released suddenly after decades or centuries of accumulated strain.

Shallow inland crustal earthquakes within the overriding South American plate are caused by internal deformation of the crust within the Andes Mountains; formed by the ongoing convergence.

Flat slab subduction beneath the Peruvian Andes also results in deformation of the South American plate, contributing to this occurrence.

[3] These earthquakes located within the South American plate (~20 km (12 mi) depth) had magnitudes of 6.5, 6.4 and 6.9 and occurred on 30 May 1990 and 4–5 April 1991, respectively.

[9] While the highest Modified Mercalli intensity was VII (Very strong) in the area for the May 1990 event, localised soil liquefaction in Rioja, Moyobamba and Soritor were assigned VIII (Severe).

Majority of the structures that suffered damage were constructed from rammed earth and adobe, particularly in Rioja, Nuevo Cajamarca and Moyobamba.

Two air force aircraft were directed by President Alan García to visit the affected region, carrying 126 tons of relief items.

[5] It was preceded by a Mw  6.4 foreshock the previous day which left 15 injured and damaged 15 dwellings in Nueva Cajamarca and Rioja.

The civil defence responded by transporting corrugated metal sheets, medical supplies, food, tents and blankets among other items.