The Pallatanga Fault is a right-lateral strike-slip fault cutting through the central Ecuadorian Andes, forming part of a larger system that accommodates the northeastward escape of the North Andean block. It runs obliquely across the mountains near the towns of Pallatanga and Riobamba, where the Nazca Plate's oblique push against South America is partly transferred inland.
The fault connects the Gulf of Guayaquil region to the inter-Andean valley, marking a zone where the sliver of crust west of the fault moves independently toward the northeast. Paleoseismic trenches dug across the fault reveal evidence of several large prehistoric ruptures, confirming its capacity for major earthquakes.
The Pallatanga Fault is widely linked to the catastrophic 1797 Riobamba earthquake, one of the deadliest in Ecuadorian history, which destroyed the old city and killed a large share of its inhabitants through shaking and landslides. Its position beneath a densely settled Andean corridor keeps it a leading seismic hazard for the country.