Aftershock analysis of the 2005 November 27 (Mw 5.8) Qeshm Island earthquake (Zagros-Iran): Triggering of strike-slip faults at the basement

From 2005 December 2 to 2006 February 26, a dense seismological network of 17 stations was installed in the epicentral region of the 2005 November 27 Qeshm sequence. The epicentral distribution of aftershocks, including an ENE-WSW trend of seismicity, is terminated on both sides by NW-SE alignments of events. The depth distribution of events (i.e., 8-20 km depth) is diffuse but in the eastern part of the aftershock zone reveals an alignment of seismicity dipping ∼40° toward the NW. Focal mechanisms of the aftershocks are strike-slip, different from that of the mainshock, which had a reverse mechanism. The scenario of a mainshock at shallow depth which is followed by a separated, deeper aftershock sequence implies different mechanisms of deformation in the sedimentary layer and the basement at the western edge of the Hormuz Strait. The epicentral distribution of aftershocks and their focal mechanisms suggest that shortening in the basement, due to convergence between Arabia and Eurasia, is accommodated in this region mainly by strike-slip motions.