The 1994 Sefidabeh earthquakes in eastern Iran: blind thrusting and bedding-plane slip on a growing anticline, and active tectonics of the Sistan suture zone

In 1994 a sequence of five earthquakes with M-w 5.5-6.2 occurred in the Sistan belt of eastern Iran, all of them involving motion on blind thrusts with centroid depths of 5-10 km. Coseismic ruptures at the surface involved bedding-plane slip on a growing hanging-wall anticline displaying geomorphological evidence of uplift and lateral propagation. The 1994 earthquakes were associated with a NW-trending thrust system that splays off the northern termination of a major N-S right-lateral strike-slip fault. Elevation changes along the anticline ridge suggest that displacement on the underlying thrust dies out to the NW, away from its intersection with the strike-slip fault. This is a common fault configuration in eastern Iran and accommodates oblique NE-SW shortening across the N-S deforming zone, probably by anticlockwise rotations about a vertical axis. This style of fault kinematics may be transitional to a more evolved state that involves partitioning of the strike-slip and convergent motion onto separate subparallel faults.