Tectonic geomorphology of High Zagros Ranges, SW Iran: an initiative towards seismic hazard assessment

Abstract

The High Zagros Ranges, SW Iran is considered to be tectonically active where damaging earthquakes have occurred. These ranges were uplifted by approximately 4550 m with respect to sea level following the collision between the Afro-Arabian and Central-Iranian plates. The Plio-Quaternary active tectonics was assessed through a detailed quantitative geomorphological study of fault-generated mountain fronts and alluvial/fluvial systems of the High Zagros Ranges. Quantitative measurement of geomorphological indices such as the stream-gradient index (SL), drainage basin asymmetry (Af), hypsometric integral (Hi), valley floor width–valley height ratio (Vf), drainage basin shape (Bs), and mountain-front sinuosity (Smf) and field data suggests a relatively medium to high degree of tectonic activity along the High Zagros Ranges. The obtained results from these indices were combined to yield an index of active tectonics (Iat). The indicative values of this index are consistent with the landforms and geology of the study area. The Iat is low to moderate in northern part of the study area which corresponds to the inactive Main Zagros Reverse Fault. The high values of Iat mainly occur in southern parts of the study area where straight mountain fronts and triangular facets along the Dena Fault suggest high tectonic activity. Moreover, the data plotted for earthquakes occurrences are consistent with morphotectonic map of relative tectonic activity and can be used as an initiative towards seismic hazard assessment. Most of the major faults are considered to be active and have potential to generate large earthquake in future and need to be evaluated more carefully for the regional seismic hazard.