Tectonic geomorphology of the Hoyran Graben (Western Anatolia, Türkiye): insights from geomorphic indices

The area between Western Anatolia and Isparta Bend comprises numerous depressions and the active faults that bound them. The Hoyran Graben is one of these depressions, located at the northernmost part of the Isparta Bend. This NE–SW-oriented graben is bounded by the Hoyran Fault in the northwest and the Uluborlu, Senirkent and Kumdanlı faults in the southeast, respectively. We evaluate the seismic activity potential among segments of the boundary faults in the light of fieldwork and morphometric indices. These boundary faults of the Hoyran Graben are divided into twelve segments for the analysis, with indices used including mountain-front sinuosity (Smf: 1.05–2.02), valley floor width-to-valley height ratio (Vf: 0.11–1.34), hypsometric curve and its integral (Hi: 0.4–0.73), asymmetry factor (Af: 13.76–87.03), stream length-gradient (SL: 1.48–9450) and normalized channel steepness (Ksn: 2.38–990.38). The results obtained, together with field observations, indicate that the Uluborlu, Senirkent and Kumdanlı faults, as well as the western segments of the Hoyran Fault, represent higher potential in terms of seismic activity with uplift rates >0.5 mm/y, while the central and eastern segments show moderate activity with uplift rates between 0.05 and 0.5 mm/y. Thus, the boundary faults of the Hoyran Graben need further attention in terms of regional seismic hazard.