Active tectonics of the Kalabagh Fault in Pakistan: implications from morphotectonics and luminescence dating

The dextral Kalabagh Fault delineates the tectonic boundary between the Kohat and the Potwar Plateausin the Himalayan frontal zone in Pakistan. Morphotectonics and dating of the seismically deformedsediments illustrate the seismic behavior and landform development of the aseismically active KalabaghFault. The overlapping zone of the two segments of the fault form a stepover along the en-echelon zone,forming a push-up block. Morphological features along the frontal part of the push-up block in theKhairabad-Ghundi segment include stream deflections, pressure ridges, stratigraphic offsets and backtiltingof the middle-late Quaternary sediments. Samples from these seismically deformed sediments weredated using the optically stimulated luminescence (OSL) dating method, with blue OSL signal from quartzand post‐infrared infrared stimulated luminescence (post‐IR IRSL) from K‐feldspar. Results from theluminescence dating were integrated with the outcrop geology and morphology that reveals thedevelopment of the push-up block occurred since c. ۰.۵ Ma. The uplift of the push-up block, coupled withthe alluvial fan development along the mountain front, has diverted the course of the Indus River westwardat a displacement rate of ۱۲-۱۵ cm/a since ~۱۵۰ ka. Deformed sediments, luminescence ages and crosscutting relationships from trenches at Khairabad denote a recurrence interval of ۱۰-۱۲ ka of earthquakesduring past ~۱۲۰ ka. The last earthquake at Khairabad occurred c. ۹ ka ago. This indicates that stressaccumulation along the Kalabagh Fault is approaching an inflection point at Khairabad, based on therecurrence periods integrated from field data and luminescence dating, which may yield majorearthquakes.