Evidence of structural segmentation of the Uttarakhand Himalaya and its implications for earthquake hazard

Abstract

The earthquake hazard associated with the Main Himalayan Thrust (MHT) is a critical issue for India and its neighbouring countries in the north. We used data from a dense seismic network in Uttarakhand, India, to model the lateral variations in the depths of MHT (2–6% drop in Vs at 12–21 km depths), Moho (a sharp increase in Vs (by ~ 0.5–0.7 km/s) at 39–50 km depths) and lithosphere (a marked decrease in Vs(~ 1–3%) at 136–178 km depths), across the Himalayan collisional front. Our joint inversion of radial PRFs and group velocity dispersion data of Rayleigh waves detects three NNE trending transverse lithospheric blocks segmenting the lithosphere in Uttarakhand Himalaya, which spatially correlate well with the northward extension of the Delhi -Haridwar Indian basement ridge, an inferred tectonic boundary and great boundary fault, respectively. Our radial receiver function imaging detects highly deformed and segmented crustal and lithospheric structures associated with three mapped transverse lithospheric blocks, suggesting a reduction in rupture lengths of future earthquakes, thereby, reducing earthquake hazards in Uttarakhand.

WITHDRAWN: Seismic Imaging of the Kumaon-Garhwal Himalaya: Insights into the Main Himalayan Thrust and the Crust-Mantle Boundary

“…). Similar models were observed at 30 out of 45 stations considered byMandal et al(2023). It can be inferred that our observation of two Ps conversions from the shallower and deeper Moho depths con rms the presence of a double Moho structure below the region.…”

“…1a, we model CCP images at a depth of 0-100 km. Here, the CCP images are built using a stacking volume of 30 (Kissling, 1995) of the 8418 P-and 8038 S-arrival times of 528 events from 10-35 stations (Fig. 1d) while the deeper part (below 40 km) of the model is taken from the ISAP91 velocity model (Kennett and Engdahl, 1991).…”

“…4a-b, P MHT , P m1 , P m2 , and P LAB arrivals have a maximum variability of 0.5-1 s for 500 velocity models, suggesting a standard deviation of 4 km in Moho 1 and Moho 2 estimates and 8 km in LAB thickness estimates. MHT thickness may vary by 3 km.Through the joint inversion of radial PRFs and fundamental mode group velocity dispersion data of Rayleigh waves,Mandal et al (2023) have obtained 1-D inverted crustal models at 45 broadband stations in the Garhwal -Kumaon Himalaya.…”

Crustal Thickness Variations and their Tectonic Implications beneath the Uttarakhand Himalayas and the adjoining Tectonic Segments: Results from 3-D Tomographic Inversion of Local and Regional Earthquake Data

“…In order to compare and produce the evidence of reliability of our recovered velocity models, we have also estimated the velocity models along the selected profiles taken from the recent published data [Gillian et al, 2015;Hazarika et al, 2021;Mandal, 2023;Mandal et al, 2023;Xu et al, 2017]. Figure 8 this also serves as another validation of our recovered velocity models.…”

“…Geological and geophysical observations demonstrate that the structural and seismic segmentation of the Himalayas is governed by lateral variations in geological structure, convergence, shortening rate, pre-orogenic sedimentary thickness, crustal thickness, erosion rates, thermal/exhumation patterns, stratigraphy, tectonic deformation pattern/style, lateral ramps along the main thrust faults, geometry of the MHT, cross-structures (e.g., DHR), and movements along the transverse faults/lineaments (e.g., RPMF, MGDF etc.) [Arora et al, 2012;Bai et al, 2019;Bollinger et al, 2004;Célérier et al, 2009;DiPietro and Pogue, 2004;Eugster et al, 2018;Gahalaut and Kundu, 2012;Gao et al, 2016;Gill et al, 2021;Gillian et al, 2015;Godin and Harris, 2014;Herman et manuscript submitted to Tectonics al., 2010;Heténeyi et al, 2016;Hubbard et al, 2021;Koulakov et al, 2015;Mandal et al, 2023;Murphy et al, 2014;Pandey et al, 1999;Prasad et al, 2011;Robert et al 2011;Stevens and Avouac, 2015;Thakur et al, 2019;Vance et al, 2003;Whipp et al, 2007;Wu et al, 1998;Yadav et al, 2019Yadav et al, , 2021Yin, 2006]. Valdiya [1976] was one of the first who put up the idea that pre-Himalayan heterogeneities in the underplated Indian basement may be the primary reason for these along-strike variations.…”