The 2010 M (sub w) 6.5 Rigan, Iran, earthquake aftershock sequence

The 20 December 2010 M (sub w) 6.5 Rigan earthquake that occurred in southeastern Iran was followed by an extensive aftershock sequence. A six-station portable seismographic network was deployed by the Institute of Geophysics at the University of Tehran around Rigan in Kerman province. To understand the aftershock activity, we have used the data recorded by this temporary seismic network. Distribution of the aftershocks shows that the earthquake sequence occurred along a right-lateral strike-slip fault with a northeast-southwest trend. The general pattern of the aftershocks distribution delineates a source fault with a length of approximately 20 km along strike and approximately 5 km across the surface. This source fault dips steeply southeastward and strikes along a nearly northeast-southwest line. The depth range of the aftershocks is 1-12 km. The aftershock activity has its highest concentration in the northern part of the active fault, and tapers off toward the southwestern part of the active fault segment, indicating mainly a unilateral rupture. On 27 January 2011, another moderate-sized earthquake (M (sub w) 6.2) occurred a few kilometers away from the southwestern end of the active zone, which probably represents a slow diffusion of stress away from the main rupture.