Quantitative Geomorphic Approach for Identifying Active Deformation in the Foreland Region of Central Indo-Nepal Himalay
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uantitative Geomorphic Approach for Identifying Active Deformation in the Foreland Region of Central Indo-Nepal Himalaya A. Misraa, K. K. Agarwala, *, G. Ch. Kothyarib, R. Talukdarb, and G. Joshia aCentre
of Advanced Study in Geology, University of Lucknow, Lucknow, 226007 India of Seismological Research, Gandhinagar, Gujarat, 382009 India *e-mail: [email protected]
bInstitute
Received November 19, 2019; revised March 16, 2020; accepted March 24, 2020
Abstract—Globally the remote sensing and geomorphometric analysis are frequently used for the assessment of tectonic activity. We used satellite-driven DEM data to analyze regional scale fluvial landform development in the parts of the central section of the Indo-Nepal Himalayan mountain chain, which is attributed the active deformation along the strike of major thrust. This deformation is accompanied by coexisting river incision and base-level fall along the longitudinal river course. These anomalies are obtained through conventional geomorphic parameters namely, stream-gradient index (SL), and steepness index (Ks) along with a new method called river Gradient Length Anomaly (GLA) analysis. GLA is a lied to deduct surface uplift and subsidence at the intersection between drainage basin and active thrusts. The deviations (offset) occurred along the river course are attributed to long-term active tectonic movement along thrust/fault or because of erosion/sedimentation processes. We analyzed 16 south-flowing rivers (e.g. Sarda, Kauriala, Girwa, and Babai), across the major Himalayan thrusts such as Main Boundary Thrust (MBT), Ramgarh Thrust (RT) and Himalayan Frontal Fault (HFT). The computed values of SL along the longitudinal course of these rivers range between 0.9‒4153 and Ks ranges from 0.1 to 173. The anomalous rise of SL and Ks values close to the major thrust points toward ongoing tectonics in the basin. The estimated results of fault parameters show that the horizontal shortening is higher than the vertical uplift. The empirical relationship of slip rate along the fault segments is estimated as 1.21, 2.65 and 1.084 mm/y respectively. Based on fault parameter, and abnormal GLA, SL and Ks analysis, and slip rate, a new E‒W oriented active fault structure have been inferred, which passes through the Beldandi, Bilsan, Bachua, Nandgaon, Dhagadhi Surat Nagar, and Bhagwanpur locations. The combined results of the present investigation can be used for evaluation of seismic hazard in the central section of Indo‒Nepal Himalayan front. Keywords: GLA analysis, neotectonics, Himalayan Frontal Fault, Main Boundary Fault, Ramgarh Thrust, Indo-Nepal Himalaya DOI: 10.1134/S0016852120040093
INTRODUCTION The Himalayan belt is undergoing deformation in contemporary times [67]. Past tectonic events have led to the formation of a foreland basin in front of the mountain chain. The basin is filled by sediments brought by Himalayan Rivers giving rise aggradational landforms such as alluvial fans and fluvial terraces [25‒27]. Intense faulting, folding and tilting of foreland d
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