Morphotectonics and paleoseismology of the western Potwar Plateau and the Kalabagh Fault (Sub-Himalayas, Pakistan)

The Sub-Himalayas in Pakistan are laterally categorized by the Kalabagh and the Jhelum Faults, bounding the Kohat and Potwar Plateaus and the Hazara Kashmir Syntaxis. The Hazara Kashmir syntaxis separates structurally and morphologically the eastern and the western Sub-Himalayas in Kashmir. The eastern Potwar Plateau and the Hazara Kashmir syntaxis have yielded recent seismicity (e.g., Mw=7.6,2005 and Mw=5.6,2019). Also, the Kohat Plateau has revealed a Mw=6 (1992) earthquake. These earthquakes designate the Kohat Plateau, the eastern Potwar Plateau and the Hazara Kashmir syntaxis as seismically active areas. Moreover, InSAR and GPS data from previous studies reveal uplift and aseismic displacements in the Salt Range, western Potwar Plateau and along the Kalabagh Fault. These anomalies suggest the area is tectonically active, that governs the landform development. This PhD thesis aims at studying the paleoseismology and neotectonics in the Sub-Himalayas with emphasis on the Kalabagh Fault, that delineates the western Potwar Plateau. The morphometric indices are evaluated in the Hazara Kashmir Syntaxis, Pir Panjal Ranges, Potwar Plateau-Salt Range, Kohat Plateau-Surghar Range and along the Kurram Fault. The landscape development in these areas is influenced by the softer lithologies of the Tertiary sediments, that are rapidly erodible and exhibit degraded morphology even for younger drainage basins. The analysis has established a comparative relation among the watersheds of these areas, denoting the landforms are differentially affected by tectonic deformations. The morphometric indices from the landforms in the Hazara Kashmir Syntaxis, Pir Panjal Ranges, Potwar Plateau-Salt Range, Kohat Plateau-Surghar Range and the western flank of the Bannu Basin reveal moderate to high tectonic activity index. Deformation history and paleoearthquakes are studied along the Kalabagh Fault using morphotectonics and paleoseismic investigations, supported by the luminescence dating of the deformed sediments. For older sediments, pIRIR luminescence dating method was applied on K-feldspar. The quartz OSL dating was employed for younger (Holocene) sediments. This study finds the tectonic deformation and seismicity that occurred during middle-late Pleistocene and Holocene. The dextral Kalabagh Fault exhibits an en-echelon zone that has formed in the overlapping area between the segments of the fault. The stepover of the en-echelon faults, that had initiated the landform development between the Thathi and Zaluch sections, had a first surface expression ~ 0.5 Ma ago. A push-up block in this en-echelon zone has formed during the past ~ 0.5 Ma. Ongoing tectonic deformations have started developing the landform since ~220 ka at Larkakki, ~140 ka at Ghundi and ~190 ka at Khairabad. This diachronous deformation has initially created meandering in the north to south flowing Indus River in the Mianwali Reentrant. Further uplifting of the push-up block has caused a tectonic tilt, diverting the course of the Indus River westward during past ~140 ka at a displacement rate of ~12-15 cm/a. The right lateral displacement in the en-echelon zone of the Kalabagh Fault exhibits morphotectonic features that include stream deflections, offsets in Quaternary sediments, pressure ridges in the foreland, displaced alluvial fans, uplifted sediments at fan apex and a piggyback basin, back tilting in the fan sediments and pebbles that are fractured and displaced. Subsurface scanning from the ground penetrating radar (GPR) and investigations from the trenches, outcrops and streams reveal splays of the Kalabagh Fault has disrupted the late Quaternary sediments during seismic events. Luminescence ages determined from these deformed sediments suggest diachronous Holocene seismicity along the Kalabagh Fault. The recurrence interval of ~10 ± 2 ka on average is calculated based on the ages of the tectonically uplifted Pleistocene sediments and youngest earthquakes at Khairabad, that has disrupted the Holocene sediments. The latest earthquakes at Khairabad in early Holocene (~ 9 ka), and during ~ 1 ka at Ghundi denote these sections of the Kalabagh Fault as tectonically active, whereas foreland is exerting stress that may lead to major seismicity at these locations. Moreover, morphometric analysis and landforms in the eastern Salt Range, Pir Panjal Ranges, Hazara Kashmir syntaxis and the Kurram Fault exhibit results that may support paleoseismic evidences in these parts of the study area