• VIKRAM GUPTA

Articles written in Journal of Earth System Science

• Seismic properties of naturally deformed quartzites of the Alaknanda valley, Garhwal Himalaya, India

The present contribution summarizes the results of a study focusing on the influence of quartz microstructures on the seismic wave velocities in the quartzites of the Garhwal Himalaya. Quartzites being monomineralic were chosen for the present study so as to nullify the effect of other mineral constituents on the seismic velocity. Samples were collected from different tectonic settings of the Higher and Lesser Himalayas which are separated from one another by the major tectonic zone ‘Main Central Thrust’ (MCT). These are mainly Pandukeshwar quartzite, Tapovan quartzite and Berinag quartzite. The samples of Berinag quartzite were collected from near the klippen and the thrust, termed as Alaknanda Thrust. The vast differences in microstructures and associated seismic wave velocities have been noted in different quartzites. It has also been observed that quartzites of the MCT zone and Alaknanda Thrust have higher seismic velocities. This is because of their coarse-grained nature of the rocks as evidenced by the strong positive relation between seismic velocities and grain area. The coarsening is either due to the operation of grain boundary migration and grain area reduction process or high aspect ratio/shape preferred orientation. The quartzites located around Nandprayag Klippen have undergone static recrystallization and exhibit the lowest seismic wave velocities.

• Geological and geotechnical characterisation of the Khotila landslide in the Dharchula region, NE Kumaun Himalaya

On 04 October 2016, a severe landslide had occurred in the vicinity of Khotila village in Dharchula, region of NE Kumaun Himalaya. This landslide may be classified as typical rockslide, involving thin veneer of debris on the slope as well as the highly shattered rockmass. The slide has been divided into three morpho-dynamic zones, viz., (i) Zone of detachment between elevation 1000 and 960 m, (ii) Zone of transportation between elevation 960 and 910 m, and (iii) Zone of accumulation between elevation 910 and 870 m. The landslide had occurred at the end of the monsoon season when the slope was completely saturated. It has been noted that the area received $\sim$88% rainfall during the monsoon months which is about two times more rainfall during 2016 monsoon than during 2015 monsoon. Geotechnical testing of the soil overlying the rockmass, corroborate the soil as ‘soft soil’ with compressive strength of 42 kPa and friction angle of 27.4$^{\circ}$. Granulometry confirms the soil as having >97% sand and silt size particles and <3% clay size particles, indicating higher permeability. Mineralogically, the soil dominantly constitutes quartz, muscovite and clinochore. Though no swelling clay minerals has been observed, the higher permeability and low strength of the soil, and concentrated higher rainfall during 2016 are the main causes for the landslide to occur. This landslide has partially blocked the flow of Kali river that serve as a boundary between India and Nepal and is endangering the habitants of the Khotila and Bangabagar villages, situated downstream in the Indian and Nepalese side of the Himalaya. In order to understand the stability of the slope, finite element modelling of the landslide has been carried out that points towards higher concentration of stresses in the landslide zone, indicating that there is further probability for the failure of landslide mass. It is therefore suggested that the landslide must be monitored continuously, particularly during the rainy season and also the risk posed by this landslide must be evaluated so as to avoid any further loss to life and infrastructure in the region.

• Landslide susceptibility mapping using bivariate statistical method for the hilly township of Mussoorie and its surrounding areas, Uttarakhand Himalaya

Landslide is a normal geomorphic process that becomes hazardous when interfering with any development activity. It has been noted that ${\sim}$400 causalities occur in the Himalayan region every year due to this phenomenon. The frequency and magnitude of the landslides increase every year, particularly in the hilly townships. This demands the large scale landslide susceptibility, hazard, risk, and vulnerability assessment of the region to be carried out. In the present study, Mussoorie Township and its surrounding areas located in the Lesser Himalaya has been chosen for Landslide Susceptibility Mapping (LSM) that involved bivariate statistical Yule coefficient (YC) method. It calculates the binary association between landslides and its various possible causative factors like lithology, land use-landcover (LULC), slope, aspect, curvature, elevation, road-cut, drainage, and lineament. The results indicate that ${\sim}$44% of the study area falls under very high, high and moderate landslide susceptible zones and ${\sim}$56% in the low and very low landslide susceptible zones. The dominant part of the area falling under high and moderate landslide susceptible zones lies in the area covered by highly fractured Krol limestone exhibiting slope ranging between 65$^{\circ}$ and 77$^{\circ}$. The study would be useful to the planners for the land-use planning of the area.

• # Journal of Earth System Science

Volume 130, 2021
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