Evidence of Strain Accumulation and Coupling Variation in the Himachal Region of NW Himalaya From Short Term Geodetic Measurements

Abstract

Himachal region of Northwest Himalaya exhibits the widest structural re‐entrant in Kangra region and significant strain partitioning along the frontal and hinterland out‐of‐sequence faults. We report results of continuous GPS measurements from 10 new sites in the region and analyze them along with the previously published results to constrain the ongoing arc‐normal and arc‐parallel convergence rates at 16.5 ± 1.1 and 4–5 mm/yr respectively. Thus, the ongoing convergence is oblique by 15°–20°. The Main Himalayan Thrust (MHT) is strongly coupled up to ∼100 km from the Main Frontal Thrust but displays significant variation in coupling in the transition zone across the Kangra re‐entrant and the adjoining western salient. Joint analysis of the coupling variation, the geologically inferred MHT geometry variations and the local topographic anomaly pattern strongly suggest the possibility of a potentially active, strain accumulating segment of MBT along the southern margin of Dhauladhar ranges in Western Himachal region, which is also proposed to be influencing the long‐term topographic growth in the region. Although a general agreement is observed between the long‐term shortening rates along the active faults and the estimated geodetic convergence in this region, the ensuing discussion highlights their complex relationship in terms of temporal and spatial variability in the fault activity and elastic‐inelastic deformation. We use the fault orientation and the estimated convergence rate to geometrically constrain a mean dextral slip‐rate of 4.4–5.7 mm/yr along a recently discovered Khetpurali‐Taksal fault, which is proposed to partition the majority of ongoing arc‐parallel deformation along it.

Comments on Kumar et al. (2023), Evidence of Strain Accumulation and Coupling Variation in the Himachal Region of NW Himalaya From Short Term Geodetic Measurements. Tectonics https://doi.org/10.1029/2022TC007690.

“…The conclusions presented in the latter-mentioned paper have been questioned in a rejoinder by Singh and Rajendran (2023) and defended by Malik et al (2023b). Below we present pointwise inconsistencies in the present study (Kumar et al, 2023) and the conclusions presented therein. We present our differing observations of the two segments of the fault system called the 'Khetpurali-Taksal' Fault (KTF-1 and KTF-2), as discussed in the paper by Kumar et al (2023) Hosted file 978631_0_art_file_11565070_s3qdr0.docx available at https://authorea.com/users/697159/ articles/685422-comments-on-kumar-et-al-2023-evidence-of-strain-accumulation-andcoupling-variation-in-the-himachal-region-of-nw-himalaya-from-short-term-geodeticmeasurements-tectonics-https-…”

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Kumar et al (2023) in their article discuss and highlight the complexities involved in the comparison of long-term and shortterm ongoing deformation in the Northwest Himalaya and their influence over the topographic evolution of the region. Their observations that rely largely on the GNSS geodetic results (Kumar et al, 2023) have also been the basis of conclusions presented in a companion paper by Malik et al, 2023a. The conclusions presented in the latter-mentioned paper have been questioned in a rejoinder by Singh and Rajendran (2023) and defended by Malik et al (2023b).

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“…2) Moreover, there is attendant evidence where the so-called KTF-1 breaks the MFT (corresponding to the Sabilpur Fault), which includes offsets preserved in geological sections, offsets on the MFT and the topography offset all of which exhibit a left-lateral sense (Nanda, 1981;Kumar and Tandon, 1985;Jukar et al, 2019;Gill et al, 2021;Kumar et al, 2022;Singh and Rajendran, 2023). 3) Further, the GNSS geodetic network of Kumar et al (2023) is not dense enough around the KTF-1 segment to clarify the sense of motion on this structure. In fact, there are no stations around the KTF-1 in a few tens of kilometers (Figure 2).…”

“…In fact, there are no stations around the KTF-1 in a few tens of kilometers (Figure 2). Further, by the authors' own admission (Kumar et al, 2023), the four sites (CHPU, SOLN, SANR, SHLS) closest to the KTF-1 segment are malfunctioning and therefore the authors decided not to use the unreliable data from these sites in subsequent analysis. In fact, one of the GNSS sites CHPU is located within a strongly deforming piedmont zone (Kim et al, 2023;Sahadevan and Pandey, 2023).…”

“…In fact, one of the GNSS sites CHPU is located within a strongly deforming piedmont zone (Kim et al, 2023;Sahadevan and Pandey, 2023). Therefore, in view of the quality of the datasets and site conditions, it is felt that Kumar et al (2023) could provide no clarity on the sense of movement, and ambiguity about the nature of slip/offset on the KTF-1 remains, both in the long-term and short-term.…”