The structure and late Quaternary slip rate of the Rafsanjan strike-slip fault, SE Iran

Abstract

The Rafsanjan right-lateral strike-slip fault in SE Iran has a clear expression in the geomorphology, is sited close to several large population centers, and yet its role in the regional tectonics, its rate of activity, and its potential to generate destructive earthquakes are unknown. We use high- resolution satellite imagery and field investigation to identify the active strands of the fault system and show that the overall north-south rightlateral shearing across the region is spatially separated into almost pure strike slip on the NW-SE-trending Rafsanjan fault and an orthogonal component of shortening on parallel thrust faults in the lowlands. Possible remnants of ruptures, involving right-lateral slip of ~3 m, from an earthquake of ~Mw >7 are identified along the eastern part of the Rafsanjan fault. We speculate that these ruptures result from the destructive 1923 Lalehzar event. An alluvial fan displaced right laterally by 48 ± 4 m and tentatively dated at ~120 ka yields an average slip-rate estimate of ~0.4 mm/yr. Our slip-rate estimate is consistent with known estimates of late Quaternary slip rate on other faults within eastern Iran and with global positioning system (GPS) measurements of present-day deformation in this part of the country. Our results therefore suggest that the slip rates of faults in eastern Iran do not vary substantially through the late Quaternary: a result that is important for the interpretation of geodetic and late Quaternary measurements of slip rate in regions of distributed strikeslip faulting. © 2011 Geological Society of America.