Morphotectonic and geodetic evidence for a constant slip-rate over the last 45 kyr along the Tabriz fault (Iran)

Abstract

Iran is an active continental domain accommodating the convergence between the Arabia and Eurasia plates. In northwestern Iran, deformation between the Central Iranian block and the Caucasus domain is mainly accommodated by right lateral strike-slip on the Tabriz fault. Cities and villages, including the city of Tabriz, have been destroyed by several strong historical earthquakes (M ∼ 7). In this study, we compare the slip-rates estimated from geodetic measurements (radar interferometry and GPS) with those determined by dating a geomorphological offset of an alluvial fan along the Tabriz fault.The GPS measurements along two profiles normal to the Tabriz fault suggest a slip-rate of 7.3 ± 1.3 mm yr −1 . The persistent scatterer radar interferometry analysis of Envisat satellite archives from 2003 to 2010 shows a velocity gradient (6 ± 3 mm yr −1 ) across the Tabriz fault in agreement with GPS results. Moreover, it reveals that most of the area located south of the Tabriz fault is affected by subsidence, and that some sections of the fault probably act as barriers to fluid migration which may have an impact on its mechanical behaviour. West of Tabriz morphotectonic investigations on an alluvial fan surface show a right-lateral cumulative offset of 320 ± 40 m. Luminescence analyses of the coarse matrix alluvial fan deposits provide an age of 46 ± 3 ka. This yields a slip-rate comprised between 6.5 and 7.3 mm yr −1 along this segment. These results suggest that the Late Quaternary slip-rate is in agreement with the present-day slip-rate estimated by geodetic measurements, showing no slip-rate changes during the past 45 000 yr. Short-term variations within the 45 000 yr related to temporal earthquake clustering over few seismic cycles cannot be ruled out, but if they exist, they do not affect the geodetic and the geomorphological estimates. This study is in agreement with previous ones suggesting that long-term slip-rates (i.e. averaged over several tens of seismic cycles) are consistent with geodetic estimated slip-rates (i.e. extrapolated from few years of interseismic observations), and suggests that perturbations of fault slip-rates are related to variations over few seismic cycles.

Paleoseismological and morphological evidence of slip rate variations along the North Tabriz fault (NW Iran)

“…However, the geodetic slip rates remain consistent with the Late Quaternary slip rates of 3.1-6.4 mm yr −1 (Hessami et al, 2003a) and ~7 mm yr −1 (Rizza et al, 2013) along the same segment of the NTF.…”

“…Our results exclude the earlier hypothesis of a spatially constant slip rate along the NTF (e.g. Masson et al, 2006;Rizza et al, 2013).…”

“…Accounting for the slip rate of 5-7 mm yr −1 derived from both the geomorphic (Hessami et al, 2003a;Rizza et al, 2013) and geodetic…”

Characterization of land subsidence in Tabriz basin (NW Iran) using InSAR and watershed analyses

“…The zero deformation point for the relative LOS map was extracted by the following reasons: (1) it is selected somewhere in east of the Tabriz basin, away from the land subsidence patterns, (2) it is selected based on high coherence values in the produced inerferograms and (3) it is selected based on the previous InSAR and GPS velocity map of the region suggested by Rizza et al (2013). The dark blue PSs are abundant at the north block of the North Tabriz Fault, associated with interseismic slip rate of the fault (Karimzadeh et al 2013;Rizza et al 2013). Two profiles with 2 km PS sampling width in the TB are drawn from north to south, perpendicular to the North Tabriz fault as a major tectonic feature of the study region.…”

Long term fault slip rates, distributed deformation rates and forecast of seismicity in the Iranian Plateau

“…Rizza et al . [] presented the current slip rates estimated from geodetic measurements (radar interferometry and GPS) on the North Tabriz Fault in northwestern Iran. They suggested the slip rates of 7.3 ± 1.3 and 6 ± 3 mm/yr deduced from the GPS measurements and the persistent scatterer radar interferometry analysis, respectively.…”