First evidence for large earthquakes on the Deshir Fault, Central Iran Plateau

Although sliced by several strike slip faults, a large part of Central Iran remained aseismic during the period of time covered by the instrumental and historical seismic records. Stating the existence of earthquakes in the Holocene is therefore important for the assessment of the regional seismic hazard. A palaeoseismic study of the Deshir fault demonstrates that Central Iran hosted large earthquakes during latest Pleistocene and Holocene. The last event corresponds to 1 m-deep fissures, which sandy infilling yielded an optically stimulated luminescence (OSL) age of 2.8 +/- 1.4 ka. At least two previous events, outlined by older fissures and/or colluvial wedges, have been recorded over the last 10-30 ka. The magnitudes are difficult to assess because the actual slips per event are unknown. The size of the fissures and the significant vertical displacement associated with a colluvial wedge are nevertheless compatible with M approximate to 7 events along a primary strike-slip surface break.