Geomorphic interpretation on the formation of strike-slip basins along the Northern Sumatran fault

Abstract

This study describes geomorphic expressions and constructs the schematic evolution of the Northern Sumatran Fault based on the development of transverse drainage basins and streams. This fault is a 400-km NW-SE right-lateral strike-slip fault with three segments, namely the Aceh and Seulimeum Faults in the northern section and the Tripa Fault in the southern section. The two faults at the northern section are sub-parallel and they link at the southeast termination of the latter fault. The examination on the geomorphic expressions comprised the fault configuration, stream deflections, and the delineation of landforms based on their genesis and geometry. This study applied drainage basin relief ratio (Rh), drainage basin volume-to-area ratio (Rva), and transverse stream profile analysis (normalized stream profile, qualitative interpretation of the profile shapes, stream concavity index (SCI), stream gradient, and knickpoint distribution) for investigating the development of transverse drainage basins and streams. For constructing the schematic evolution, this study evaluates drainage maturity level from the applied methods to interpret relative timing of basin formation. This study suggests that the Aceh and Tripa Faults constituted the initial configuration and they propagated to the southeast and northwest, respectively, before merging. The Seulimeum Fault, which formed subsequently, propagated to the northwest after merging with the Aceh Fault at its southeast termination. This study also infers that fault section with lower drainage maturity coincides with greater numbers of earthquakes.