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<p>During field investigations in the Aripal river basin, near Laam area of Tral, a bedrock fault rupture that dips perpendicular to the bedding planes was observed on the south facing ridge top, composed of Limestone beds at an elevation of 2325&#xa0;m above mean sea level. Geographically, the fault rupture is located between the latitude 34° 02′ 27.87′′N and longitude 75° 04′ 45.04′′ E nearly 20&#xa0;km NW of Tral, the tehsil headquarters. The 3&#xa0;km long fault rupture, parallel to the ridge with a maximum displacement of 20&#xa0;m, has offset the southern slope of the ridge and has generated the fault scarp that strikes 15° and dips 85° SE. During intensive and repeated field investigations, a large outcrop scale minor syn-tectonic fault related features like fault striations/slickenlines, grain supported cataclastic rocks and augen shaped crystals (cockade) on the foot wall and highly sheared zone fault gouge along the fault plane were identified. In addition to the direct evidences, some indirect features (tectonic landforms) were also observed indicating kinematics of the area. These geomorphic indicators include: linear drainage, triangular facets, ~ 20&#xa0;m high waterfall, braided bar deposits and unpaired river terraces. Moreover, the longitudinal profile of the river also suggests the presence of knick point in the respective segment where the probable extension of this fault is inferred. Also, a massive rock fall and land slip has been observed towards northeast and southwest of the Laam area respectively, which suggests that the area might have been shaken by an earthquake in the past. Sub surface geophysical surveys were employed to find the probable extension and nature of this fault. Three 2D Ground Penetration Radar (GPR) profiles oblique to the fault strike of different dimensions were acquired using 100&#xa0;MHz (RTA) and 250&#xa0;MHz shielded antenna. The radarograms clearly display the fault offset decreases towards southwest of the ruptured surface and the dip also decreases from 85° to &lt; 45° which allows to infer the fault is of the Listric type. However, correlating the surface expressions of fault in the quaternary fluvial systems and landforms with significant surface deformation in the recent deposits and subsurface studies suggests the fault is active and has 5&#xa0;km more extension towards southwest. The present study, which focuses on the delineation of fault and its spatial extension, approximately more than 8&#xa0;km, will provide critical baseline data for quantifying paleo-earthquake magnitude that in turn will be used for micro-seismic zonation of the Kashmir Basin in particular and NW Himalaya as whole. Using empirical relationships that are dependent on fault related parameters like fault rupture length (L) and total displacement (MD) an attempt has been made to quantify the magnitude of the paleo-earthquake which possibly has developed such a spatial surface deformation, large scale rockfall and landslip in the area.</p>

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Rupture length as a proxy for quantifying palaeo-earthquake magnitude for future seismic micro-zonation in Kashmir, NW Himalaya, India

  • 期刊论文

  • 发表日期：

    2025年3月22日

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  • Bikram Singh Bali,
  • Ahsan Afzal Wani,
  • Sareer Ahmad Mir,
  • Mohammad Irfan,
  • Dansita Farooq

摘要

During field investigations in the Aripal river basin, near Laam area of Tral, a bedrock fault rupture that dips perpendicular to the bedding planes was observed on the south facing ridge top, composed of Limestone beds at an elevation of 2325 m above mean sea level. Geographically, the fault rupture is located between the latitude 34° 02′ 27.87′′N and longitude 75° 04′ 45.04′′ E nearly 20 km NW of Tral, the tehsil headquarters. The 3 km long fault rupture, parallel to the ridge with a maximum displacement of 20 m, has offset the southern slope of the ridge and has generated the fault scarp that strikes 15° and dips 85° SE. During intensive and repeated field investigations, a large outcrop scale minor syn-tectonic fault related features like fault striations/slickenlines, grain supported cataclastic rocks and augen shaped crystals (cockade) on the foot wall and highly sheared zone fault gouge along the fault plane were identified. In addition to the direct evidences, some indirect features (tectonic landforms) were also observed indicating kinematics of the area. These geomorphic indicators include: linear drainage, triangular facets, ~ 20 m high waterfall, braided bar deposits and unpaired river terraces. Moreover, the longitudinal profile of the river also suggests the presence of knick point in the respective segment where the probable extension of this fault is inferred. Also, a massive rock fall and land slip has been observed towards northeast and southwest of the Laam area respectively, which suggests that the area might have been shaken by an earthquake in the past. Sub surface geophysical surveys were employed to find the probable extension and nature of this fault. Three 2D Ground Penetration Radar (GPR) profiles oblique to the fault strike of different dimensions were acquired using 100 MHz (RTA) and 250 MHz shielded antenna. The radarograms clearly display the fault offset decreases towards southwest of the ruptured surface and the dip also decreases from 85° to < 45° which allows to infer the fault is of the Listric type. However, correlating the surface expressions of fault in the quaternary fluvial systems and landforms with significant surface deformation in the recent deposits and subsurface studies suggests the fault is active and has 5 km more extension towards southwest. The present study, which focuses on the delineation of fault and its spatial extension, approximately more than 8 km, will provide critical baseline data for quantifying paleo-earthquake magnitude that in turn will be used for micro-seismic zonation of the Kashmir Basin in particular and NW Himalaya as whole. Using empirical relationships that are dependent on fault related parameters like fault rupture length (L) and total displacement (MD) an attempt has been made to quantify the magnitude of the paleo-earthquake which possibly has developed such a spatial surface deformation, large scale rockfall and landslip in the area.