The destructive earthquake, Ms = 7.1 (BRK), occurred at 0537 a.m. local time, near an agricultural center in the mountainous Zagros Range of the Fars Province in the south of Iran. Leveling virtually all structures in the epicentral region, the shock killed nearly 25 per cent of the population of about 23,000 people in the devastated villages within a radius of about 50 km from the epicenter. Hardest hit was the valley complex of Qir, Karzin, and Afzar. The high percentage of death was mainly caused by structural failure and the collapse of the heavy roof of almost all adobe and masonry residential structures in the area. Structural failure of buildings with modern steel-beam roofs and of the traditional adobe and masonry-walled buildings with heavy timbered roofs in the region was due primarily to the lateral shear failure of poorly constructed adobe and masonry, lack of earthquake-resistant vertical load-carrying columns or elements, and lack of bracing and adequate tie-in in the roofs. Engineered buildings also collapsed, generally, because of defects in engineering and construction practices. Only minor cases of ground failure were observed, mainly slides in steep mountainous regions and some collapse of steep banks of rivers and irrigation channels.