LATE QUATERNARY SLIP-RATE ON THE GOWK FAULT OF EASTERN IRAN

We provide the first quantitative estimate of the late Quaternary slip-rate on the Gowk strike-slip fault in eastern Iran. The main active strand of the fault cuts lakebed sediments within the South Golbaf pull-apart basin. Numerous channels incised into the palaeo-lake surface are displaced right-laterally by 30 +/- 5 m at the fault. Radiocarbon and optical (OSL) dating of the lake desiccation allows us to estimate a slip-rate of ~4.5 mm/yr. This estimate is considerably higher than the previously assumed value of ~2.5 mm/yr and indicates that the Gowk fault is the most important structure in the accommodation of regional tectonic strain in eastern Iran. Our slip-rate on the Gowk fault accounts for previously suggested regional discrepancies between geodetic and longer-term estimates of fault slip across eastern Iran, and argues against temporal variations in slip-rate within the Holocene.

Our result is also important for the assessment of earthquake hazard. The Gowk fault has generated five destructive earthquakes in the past thirty years. At a rate of ~4.5 mm/yr the average interval between earthquakes, assuming that the fault typically fails in events involving ~3 m of slip, will be ~700 years. The southern 90 km of the Gowk fault (the Sarvestan segment) has no record of historical earthquakes and constitutes a considerable remaining hazard in this region.