The southern Iran earthquake of April 10, 1972 (Ms = 6.9) killed more than 5,000 people in the region of Ghir, Fars Province, in the folded belt of the Zagros Mountains. Aftershocks of the earthquake, relocated with respect to the hypocenter of the main shock by the method of joint hypocenter determination, and the radiation pattern of P and S waves suggest that the earthquake occurred on a west-northwest-striking reverse fault. This fault had a moderate dip and a strike that was parallel to the local trend of the folds and thrust faults of the Zagros folded belt, which are of latest Cenozoic (Pliocene and Quaternary) age. The inferred fault rupture of the main shock propagated approximately 35 km east-southeast from its epicenter, terminating in the epicentral region of a Ms = 5.6 earthquake that occurred on September 14, 1968. The zone of heaviest damage to adobe structures follows closely the trend indicated by the relocated epicenters of the main shock and principal aftershocks. Beyond 25 km from this trend, damage to adobe structures was negligible.