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Himalayan Geology, Vol. 43 (1B), 2022, pp. 140-150, Printed in India

Geodetic strain rate, slip deficit and seismicity analysis in Central Seismic Gap of the Himalayan arc

SAROJ K. MONDAL, RAJEEV K. YADAV, AMIT K BANSAL, JOSHI K. CATHERINE,

VINEET K. GAHALAUT*

CSIR-National Geophysical Research Institute, Hyderabad - 500 007, India

*Email (Corresponding author) : vkgahalaut@yahoo.com

Abstract: Geodetic strain rate measurements and the crustal stress analysis are very important for seismic hazard assessment in the Central seismic gap of Himalaya and its adjoining regions because of densely populated region and its very long history of accumulation of elastic strain energy. Measurements of principal strain tensors and degree of locking (or interseismic coupling) is carried out using geodetic data form 29 continuous Global Positioning System (cGPS) sites in Kumaun-Garhwal region, 24 sites installed by CSIR-NGRI Hyderabad, 7 permanent sites from western Nepal and 50 campaign mode observations reported in past studies. Our precise velocity field measurements in the Kumaun Garhwal Himalaya yields 17.5±0.7 mm/yr of plate convergence rate and ~90-110 km of locking width of the frontal Main Himalaya Thrust (MHT). We derive geodetic strain rate, locking heterogeneity and crustal stress variation from these measurements to understand the geodynamics of crustal behaviour in this region for accessing the potential seismic hazardous regimes. We also calculated b-value utilizing seismicity catalogue to assess crustal stresses in the region. We applied weighted least-square inversion approach to calculate the degree of locking (interseismic coupling) on the MHT that results highly coupled (>0.6) frontal part of MHT with varying width of locking (70-90 km) across the main structural trend in the Kumaun-Garhwal Himalaya. We observe high strain rate (102 nano strain/yr) in the Higher Himalaya that gradually decreases towards south up to Himalayan front as well as towards north in the Tethys Himalaya. Spatial variation in the principal strain rate in the northwest Himalaya is also observed. Western zone (Block A, comprising of Himachal and Garhwal region) of northwest Himalaya is found to have relatively high average geodetic strain rate (110 nano strain/yr) as compared to average strain rate (67 nano strain/yr) in the eastern zone (Block B comprising of Kumaun and western Nepal region). However, the zones under high geodetic strain rate (block A) and low strain rate (block B) are observed to have relatively low and high crustal stress respectively, as indicated by the b-value.

Keywords: Earthquakes, GPS, principal strain rate, interseismic coupling, Himalaya seismicity

 
 
 
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