Earthquake source parameter estimation using synthetic waveform modelling

Fault plane solutions and focal depths for three crustal events occurring in the Himalayan collision zone have been obtained using synthetic waveform modelling. Two crustal events with their epicenters in the Tibetan plateau show large component of normal faulting with east-west trading T-axes. The third event with It’s epicenter north of Main Boundary Thrust (MBT) shows reverse faulting with the nodal planes paralleling the local structural trend. All the three crustal events studied have occurred at shallow focal depths of less than 15 km. The Inferred source parameters of these events are discussed In the light of active tectonics of the region.

Carbonate clumped isotope thermometry of fault rocks and its possibilities: tectonic implications from calcites within Himalayan Frontal Fold-Thrust Belt

Disentangling the temperature and depth of formation of fault rocks is critical for understanding their rheology, exhumation, and the evolution of fault zones. Estimation of fault rock temperatures mostly relies on conventional geothermometers of metamorphic minerals and element partitioning analysis, which are largely inapplicable in shallow crustal fault rocks. Here, we demonstrate the applicability of the carbonate clumped isotope thermometer in low-grade carbonate-bearing fault rocks from the Himalayan frontal wedge (northwest India). Coalescing carbonate clumped isotope thermometry and calcite e-twin morphology allows us to constrain the temperature and depth of formation of the two main thrusts of the Himalayan frontal wedge, the Nahan thrust (170 ± 10 °C; 6–7 km depth), and the Main Boundary thrust (262 ± 30 °C; 10–11 km depth). The integration of the adopted analytical techniques can promote the application of calcite-based clumped isotope thermometry to the fault zone processes and refinement of shallow crustal fault zone models.

Geological and Geotechnical State of the Nisane Khola Landslide, Dharan, Sunsari, Nepal: a case study

Geological and landslide mapping was carried out in order to delineate the geological and geotechnical state of the Nisane landslide, situated in Dharan Sub-Metropolitan City, Sunsari, Nepal, which has been obstructing the Koshi Highway time and again. The affected area bears metasedimentary and sedimentary rock sequences of the Lesser Himalaya and the Siwalik, respectively. The Dharapani Thrust separates the Chiuribas Formation and the Tamrang Formation of the Lesser Himalaya whereas the Main Boundary Thrust separates the Tamrang Formation and the Siwalik. The Nisane landslide is an old landslide situated in the structurally weak zone having variable activation period. Recently, the landslide reactivated as intense slide after the Gorkha Earthquake, 2015 and is occasionally obstructing the Koshi Highway. The subsidence in highway indicates the landmass is creeping along the tension crack. Kinematic analysis, Rock Mass Rating (RMR) and Slope Mass Rating (SMR), based on the field observation, measurement and laboratory testing, was carried out in eight different slopes of the slide. The results suggested majority of slopes suffers the wedge and plain failures along the major joint sets. The rock masses are of fair class and the slopes are unstable to partially stable. The slopes of major slide are vulnerable and seeks for immediate sustainable treatment.

Balanced cross-section across the Siwaliks of the Trijuga Valley, eastern Nepal

The strata of the Siwalik Group in the Trijuga valley is dissected by two thrusts, repeating the succession three times and forming a longitudinal Dun Valley. The total thickness of the Siwalik strata exceeds 5000 m in the area. A balanced cross-section has been constructed across the Siwalik Range in the Trijuga valley showing that the Main Himalayan Thrust (MHT) lies at the depth of about 5.2 km from the surface. The Main Frontal Thrust (MFT), Kamala Tawa Thrust (KTT), Marine ­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­­Khola Thrust (MKT) and Main Boundary Thrust (MBT) ramp-up from the MHT. Along with these faults, fault-bend anticlines associated with these thrusts have shortened the Siwalik of the area. The shortening across the area has been calculated to be approximately 33.7 km.