Morphotectonic modeling of the Ibagué strike-slip fault, Colombia

Abstract

The Ibagué Fault is a dextral strike-slip fault which runs in an ENE direction. It is by far the most notable feature of a transverse shear zone, which affects the Central Cordillera of the Colombian Andes. The fault, on leaving the east flank of the Cordillera, crosses an extensive alluvial plain of largely Pleistocene age, known as the Ibagué Fan. It is along this stretch across the plain that the fault displays abundant morphologic features characteristic of strike-slip movement. The fault, as seen in remote sensing imagery and on aerial photos, appears as one continuous trace, but closer inspection reveals that in fact it is in most places made up of sequences of synthetic dextral Riedel shears connected by pressure ridges varying greatly in size. A photogeologic survey followed by fieldwork permitted the selection of a suitable site for the excavation of a trench for a paleoseismological study in a small pull-apart basin not affected by human activity. Preliminary inspection of the trench outcrop revealed a stratigraphic section recording eight seismic events during the Holocene.