The Naghan earthquake of magnitude 6 (Ms) occurred on 6 April 1977 in the mountainous area of Chahar Mahal Bakhtiari in the High Zagros, south of Shahr-e-Kord. It killed 348 people, injured about 200, and caused destruction over an area of 150 Km2. The shock damaged beyond repair 2,100 houses and killed 0.7% of livestock in the area; eight schools collapsed and 37 were damaged. The maximum intensity of the main shock did not exceed VI11 (MM).
The earthquake was associated neither with any fresh surface faulting, nor with reactivation of the existing faults and salt domes at surface. Heavy rain fell before and during the earthquake and the destruction was more extensive where the saturated clay content of the alluvium was higher; it was also more extensive in water-logged areas or the areas with a shallower water table. Landslides occurred on steep slopes and destroyed or damaged some villages built on slopes. Several aftershocks caused additional damage to the already destroyed or damaged villages.
The Naghan earthquake was another instance of the "Subsedimentary Zagros-Type Earthquake" in the High Zagros part of the Zagros Active Folded Belt, indicating that the re-adjustment of the unexposed metamorphosed Precambrian Basement at depth caused no tectonic deformation (surface faulting) at the top of the sedimentary cover. This was due to the presence of the Upper Precambrian Hormoz layers (Salt deposits) acting as a slippage zone along the decollement surface of the Zagros at depth.