Estimation of the relative active tectonics in Shahriary basin (Central Iran) using geomorphic and seismicity indices

Iran is well known for having countless historical and instrumental records of tectonic events. Shahriary catchment, as a study area, is part of the Zagros collision seismic province. This research aimed to introduce a new method which is useful in identifying the relative active tectonic events of an area. The research method was designed in order to calculate the relative active tectonic index (IRAT) using geomorphic and seismicity indices. Accordingly, IRAT was determined based on the river length–gradient index (SL), drainage basin asymmetry (AF), transverse topographic symmetry factor (TP), hypsometric integral (HI) and the drainage basin shape index (BS). The obtained results showed that areas with relatively high, moderate and low tectonic activities comprised 71%, 19% and 10% of the study area, respectively. In addition, the calculated mean seismicity in Shahriary was 4.8±0.2 Ms, with an acceleration gravity of 0.3 g (i.e., a high-risk zone). The resultant data confirmed the ability of seismicity indices to estimate IRATs. Therefore, application of the proposed method for assessing the IRAT of an area is confidently recommended in watershed management planning.