An investigation of the Dasht-e Bayāz, Iran earthquake of August 31, 1968

Abstract

abstract On Augus>t 31, 1968 at 10:47:37.4 G.M.T., the Khorassan Province of northeastern Iran was shaken by one of the most destructive earthquakes in Iranian history. The epicenter of the earthquake was about 250 kilometers south-southwest of Mashad, approximately 10 kilometers east of the measured surface fault. Its magnitude (Ms) was 7.3. A field investigation revealed that a number of villages were extensively damaged or destroyed, resulting in about 10,000 fatalities> and 60,000 homeless residents. Surface fractures were noted in several areas. Maximum horizontal displacement was a left-lateral movement of 4.1 meters east of Dasht-e Bayāz. The measured fault length was 25 kilometers. Inaccessibility to part of the area and a time limitation factor curtailed a more complete analysis of the possible fault extensions both to the west and east. The extensive property damage is attributed principally to poor construction in the region. However, the location of some of the villages on alluvium with a shallow water table was a contributing factor in some instances. In particular this paper analyzes the regional intensities, the effects on local structures, and the fresh surface faulting phenomenon resulting from the earthquake. Also presented are the results of the investigations on the temporal, spatial, and magnitude characteristics of all recorded seismic activity, before, after, and including the major event.