Active faults and related Late Quaternary deformation along the Northwestern Himalayan Frontal Zone, India

J. N. Malik, T. Nakata

Abstract


Numerous newly-identified traces of active faults in the Himalayan foothill zone along the HFF around Chandigarh, in
Pinjore Dun, along the piedmont zone of the Lower Siwalik hill front and within the Lower Tertiary hill range reveal the
pattern of thrust and strike-slip faulting, striking parallel to the principal structural trend (NNW-SSE) of the orogenic
belt. The active Chandigarh Fault, Pinjore Garden Fault and Barsar thrust have vertically dislocated, warped and backtilted
fluvial and alluvial-fan surfaces made up of Late Pleistocene-Holocene sediments. West- and southwest-facing
fault scarplets with heights ranging from 12 to 50 m along these faults suggest continued tectonic movement through
Late Pleistocene to recent times. Gentle warping and backtilting of the terraces on the hanging wall sides of the faults
indicate fault-bend folding. These active faults are the manifestation of north-dipping imbricated thrust faults branching
out from the major fault systems like the Main Boundary Fault (MBF) and Himalayan Frontal Fault (HFF), probably
merging down northward into a décollement. The Taksal Fault, striking NNW-SSE, shows prominent right-lateral movement
marked by lateral offset of streams and younger Quaternary terraces and occupies a narrow deep linear valley along
the fault trace. Right stepping along this fault has resulted in formation of a small pull-apart basin. Fault scarplets facing
ENE and WSW are the manifestation of dip-slip movement. This fault is an example of slip-partitioning between the
strike-slip and thrust faults, suggesting ongoing oblique convergence of the Indian plate and northward migration of a
tectonic sliver. Slip rate along the Taksal Fault has been calculated as 2.8 mm/yr. Preliminary trench investigation at the
base of the Chandigarh Fault Scarp has revealed total displacement of 3.5 m along a low angle thrust fault with variable
dip of 20° to 46° due northeast, possibly the result of one large magnitude (Mw 7) prehistoric earthquake. Taking into
consideration the height of the Pinjore surface (20 to 25 m), tentative age (8.9 ± 1.9 ka), displacement during one event
and average angle of fault dip (25°) gives slip rate of about 6.3 ± 2 mm/yr, a rate of horizontal shortening of 5.8 ± 1.8
mm/yr and recurrence of faulting of 555 ± 118 years along the Himalayan Frontal Fault.

Keywords


active faults;Northwestern Himalayan Front;paleoearthquake;thrust and right lateralstrike-slip faults;slip-partitioning

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References


DOI: https://doi.org/10.4401/ag-3462
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X