Geomorphic Signatures of Active Tectonics in the Jarahi-Hendijan Drainage Basin (Marun-Zohreh Rivers) in South-West Iran

This paper aims at evaluating relative active tectonics in the Jarahi-Hendijan drainage basin based on geomorphic indices. Indices used include: stream length-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), ratio of valley-floor width to valley height (Vf), index of drainage basin shape (Bs), and index of mountain front sinuosity (Smf). Results the analyses were combined to achieve an index of relative active tectonics (Iat), which is divided into four classes implying relatively low to very high tectonic activity. The study area is located across the Zagros Mountains belt (high Zagros, folded belt, and frontal lowlands) in southwest Iran, and comprises an ideal location to test the concept of an index to predict relative tectonic activity on a basis of area rather than a single valley or mountain front. Recent investigations show that neotectonism has played a key role in the geomorphic evolution of this part of the Zagros ranges. Geomorphic indices indicate the presence of differential uplifting in the geological past. Higher values of Iat (low tectonic activity) mainly occur in the southwest of the Jarahi- Hendijan drainage basin, while the rest of the study area falls into classes of Iat that indicate moderate to high tectonic activity. Baghmalek and Takhtderaz sub-basins show the highest values of relative tectonic activity. The distribution of this index defines areas associated with different faults and relative rates of tectonic activity. Nearly 40% of the study area is classified into Classes 1 and 2 implying very high to high tectonic activity, and 37% is grouped as Class 4, which is taken to indicate low tectonic activity. Areas of higher relative tectonic activity represent lower Iat values.