Morphometric Evaluation of the Relative Uplift Rates along the Vigan–Aggao Fault in Ilocos Norte, Philippines

The Vigan–Aggao Fault (VAF) in northern Luzon Island is a NNE-trending sinistral fault divided by fault bends, which are associated with local variations in the fault’s kinematics. In this study, we examined the relative uplift rates across the fault bend in the San Juan–Vintar segment of the VAF using morphometric indices. Basin-based indices, namely hypsometric integral, basin shape, basin elongation ratio, and basin asymmetry factor, and non-basin-based indices, namely stream length-gradient index, normalized stream length-gradient index, and mountain front sinuosity were calculated to isolate and examine the surface processes that influence landscape development. We then integrated the basin-based results with geological data to create a relative tectonic activity index (RTAI). Clustering analysis of the results revealed hotspots along the bent section of the fault indicating more values that suggest higher relative uplift rates during the development of the landscape. The morphometric indices showed that the highest uplift rates are along the central VAF strands. This study described and evaluated the relative uplift rates of a known active fault system in Ilocos Norte, in the absence of detailed field structural data. This study also reinforces the utility of morphometry in identifying priority sites for detailed paleoseismic and seismic hazard analyses.