Morphotectonics and geodetic evidences for a constant slip-rate along the Tabriz Fault(Iran) during the past 45 kyr

Iran is an active continental domain accommodating the convergence between the Arabia and Eurasia plates. In the north-western part of Iran, the deformation between the Central Iranian Block and the Caucasus domain is mainly accommodated by right lateral strike-slip on the Tabriz fault. The Tabriz fault produced several strong destructive earthquakes (M ~7) during historical times. In this study, we determine and compare the slip rate along the Tabriz fault estimated from a morphotectonics study and from geodetic measurements (PS-InSAR and GPS). West of the Tabriz city, along the central segment of the Tabriz fault, morphological investigations on an alluvial fan surface show a right-lateral cumulative offset of 312 ± 6 m. Luminescence analyses of the coarse matrix alluvial fan deposits (250-180 microns) provide an age of 45.8 ± 3.06 ka. This yields a slip rate comprised between 6.3 and 7.5 mm/yr along this segment. The PS-InSAR analysis of Envisat satellite archives from 2003 to 2010 shows a velocity gradient across the Tabriz fault suggesting a slip rate of 5-7 mm/yr. This is consistent with the 1999-2009 measurements GPS, which suggest a slip rate of ~7 mm/yr on the Tabriz fault. The geological slip-rate and the present day slip-rate determined by geodetic measurements are equal (~7 mm/yr), suggesting that the slip rate remains constant along the Tabriz fault during the past 45,000 years. This fault slip rate is also consistent with a 250-300 yrs recurrence time interval for magnitude 7-7.3 earthquakes, as suggested by the historical seismicity of the Tabriz fault.