Active faulting and seismicity of the Dasht-e-Bayaz region, eastern Iran

Abstract

The Dasht-e-Bayaz left-lateral strike-slip fault system in NE Iran ruptured over a length of ca 120 km during two earthquakes in 1968 and 1979. We constrain source parameters of the 1968 August 31 (Dasht-e-Bayaz) and 1979 November 27 (Khuli-Buniabad) earthquakes by analysing long-period body wave seismograms. Both earthquakes involved complex rupture processes, with at least two subevents in each case. Coseismic surface ruptures and cumulative scarps in alluvium indicate fault segmentation on numerous short (ca 20 km long) strands with small pull-aparts between them. The earthquake subevents seen in the seismograms probably relate to this segmentation. The total, cumulative, offset on the fault system is estimated at ca 4-5 km. This is small compared to the total amount of Late Tertiary deformation expected in this part of Iran, and indicates that the Dasht-e-Bayaz fault may be relatively young. Distributed strike-slip faulting is widespread in the region and there are indications that the Dasht-e-Bayaz fault is evolving from several short faults that are coalescing. These results are important not only for understanding of the regional tectonics but for the development and evolution of strike-slip faults in general. © 2004 RAS.