The Precordillera Thrust Front is a system of east-verging reverse faults along the eastern margin of the Andean Precordillera in the provinces of San Juan and Mendoza, western Argentina. These thrusts push older rocks up and over the younger sediments of the foreland, building the low mountain ridges that flank the populated valleys.
The faulting is driven by the shallow, flat subduction of the Nazca Plate beneath this segment of the Andes, which transmits compression far inland and reactivates a broad zone of crustal shortening. Faults such as those near Villicum and Zonda progressively fold and uplift the landscape at rates of a few millimetres per year.
This thrust front generated the catastrophic 1944 San Juan earthquake (magnitude ~7.0), which destroyed much of the city of San Juan and killed roughly 10,000 people, making it Argentina's deadliest natural disaster. The event underscored the danger posed by the shallow reverse faults hidden beneath the region's cities.