Makran coast: A potential seismic risk belt

Abstract

The Makran coast is located along an active plate boundary lying in the offshore region where Arabian plate is being actively subducted northwards beneath Afghan and Lut blocks. The active margin of Makran Coast remained a site of earthquakes throughout the historical and modern times. This scenario warrants a seismotectonic analysis of the Makran coastal areas to asses risk factors both for human settlements as well as important civil structures The reconnaissance gismo tectonic studies along the Makran coast resulted in the identification of a number of seismites of Holocene times associated with capable faults. The instrumental and historic seismicity catalogue reveals that the Makran coast active margin is marked by low seismicity presently clustered in the south of Pasni. The infrequent large events occurred all along the Makran coast. The event 1945 (magnitude 8.1) with shallow depth of 25 km located near Pasni caused ground ruptures, modification of landscape, rock falls, liquefactions, fire and 5 to 10 m high tsunami.

The Makran coastal areas are divided into seven seismotectonic zones. The Makran coastal belt falls within one of these zones, in which main seismogenic structures are subduction related thrusts. A number of capable faults have also been recognized. The studies indicate significant seismic risk to the coastal areas. Presently the stresses are indicated to be accumulating in Gwadar area. It is therefore suggested that sites for important civil structures should be selected on the basis of geological and seismotectonic studies. The antiseismic design parameters for each structure should be adopted as per international codes and criteria for seismically active areas.