• An estimation of probable seismic hazard in the active deformation front of the Himalayan arc

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      https://www.ias.ac.in/article/fulltext/jess/130/0043

    • Keywords

       

      Himalaya; Main Himalayan Thrust (MHT); geodetic moment rate (Mgd); seismic moment rate (Msm); moment ratio (Mgd/Msm); seismic vulnerability.

    • Abstract

       

      In this study, the strain rate (SR) in grid-nodes in and around Himalaya that was computed from 1252 GPS station data, is also used. The earthquake catalogue of Himalaya between 1225 and 2017 is compiled. The active tectonic front of the Himalaya is subdivided into 14 zones between MFT and MCT, where MHT is locked. For each zone, magnitude-completeness ($M_{c}$), ‘a’ and ‘b’ values, geodetic moment rate (Mgd), seismic moment rate (Msm), moment ratio (Mgd/Msm) are calculated. It is observed that the moment ratio is <1 in zone 1 (Kashmir), 3 (Kangra), 5 (Almora), 6 (Central-gap 1), 8 (Pokhra–Kathmandu), 9 (Everest), 11 (W Bhutan), 12 (E Bhutan), 13 (Arunachal) and 14 (Eastern Syntaxis). These zones show good agreement between geodetic and seismic moment rates, and are vulnerable to large earthquakes ($M_{w}$ 8.15–8.95) in the distant future. Presently, zone 2 (Kishtwar), 4 (Nahan), 7 (Central-Gap 2), and 10 (Sikkim) are vulnerable as they show moderate-low b-values, high moment ratio (>1), and long seismic hiatus for large earthquakes. Moreover, zones 2, 4, 10, 12, and 13 have un-ruptured patches of MHT and have the capacity to spawn $M_{w}$ 6.75–7.95 earthquake at any point of time. The rupture generated in these zones will transgress the zone boundaries and terminate in the sub-surface Precambrian ridge systems continuing from Peninsular India below Himalaya.

      $\bf{Highlights}$

      $\bullet$ The earthquake catalogue of Himalaya between 1225 and 2017 is compiled.

      $\bullet$ The active tectonic front of the Himalaya is subdivided into 14 zones (1–14) between MFT and MCT.

      $\bullet$ The moment ratio < 1 in 10 zones [1 (Kashmir), 3 (Kangra), 5 (Almora), 6 (Central-gap1), 8 (Pokhra–Kathmandu), 9 (Everest), 11 (W Bhutan), 12 (E Bhutan), 13 (Arunachal) and 14 (Eastern Syntaxis)], show good agreement between geodetic and seismic moment rates, and are vulnerable for large earthquake ($M_{w}$ 8.15–8.95) in distant future.

      $\bullet$ Presently, zones 2 (Kishtwar), 4 (Nahan), 7 (Central-Gap 2) and 10 (Sikkim) are vulnerable as they show moderate-low b-values, high moment-ratio (7gt;1) and long seismic hiatus. Moreover, zones 2, 4, 10, 12 and 13 have un-ruptured patches of Main Himalayan Thrust (MHT) and have capacity to spawn $M_{w}$ 6.75–7.95 earthquake any point of time.

      $\bullet$ The rupture generated in these zones will transgress the zone boundaries and terminate in the sub-surface Precambrian ridge systems continuing from Peninsular India below Himalaya.

    • Author Affiliations

       

      BASAB MUKHOPADHYAY1

      1. Geological Survey of India, Central Headquarters, 29 J L Nehru Road, Kolkata 700 016, India.
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