Earthquake Stability Analysis of Rock Slopes: a Case Study

Stability analysis of Surabhi landslide in the Dehradun and Tehri districts of Uttaranchal located in Mussoorie, India, has been simulated numerically using the distinct element method focusing on the weak zones (fracture). This is an active landslide on the main road toward the town centre, which was triggered after rainfall in July–August 1998. Understanding the behaviour of this landslide will be helpful for planning and implementing mitigation measures. The first stage of the study includes the total area of the landslide. The area identified as the zone of detachment is considered the most vulnerable part of the landslide. Ingress of water and increased pore pressures result in reduced mobilized effective frictional resistance, causing the top layer of the zone of detachment to start moving. The corresponding total volume of rock mass that is potentially unstable is estimated to 11.58 million m³. The second stage of this study includes a 2D model focussing only on the zone of detachment. The result of the analyses including both static and dynamic loading indicates that most of the total displacement observed in the slide model is due to the zone of detachment. The discontinuum modelling in the present study gives reasonable agreement with actual observations and has improved understanding of the stability of the slide slope.     

Linkage of paraglacial processes from last glacial to recent inferred from Spituk sequence,Leh valley,Ladakh Himalaya

The paraglacial sequence in the Leh valley, Ladakh Himalaya preserves imprints of various processes active during deglaciation in the late phase of Last Glacial. In present work, a high resolution sedimentological record generated for Spituk is presented identifying aeolian episodes, mudflow events from Ladakh Range and debris flows extending from Zanskar Range across present Indus River. Two temporal phases of water ponding within Spituk Sequence are also identified. The seismites recorded at various stratigraphic depths and their association with the sediment facies signifies gravity induced process besides possible seismic activity as an added phenomena. Linkage between paraglacial processes since Last Glacial to Recent is tracked and evaluated.     

Paleo-uplift and cooling rates from various orogenic belts of India, as revealed by radiometric ages

The significant discordance of the radiometric (Rb-Sr, Pb-U, K-Ar and fission track) ages from various orogenic cycles of the Dharwar, Satpura, Aravalli and Himalayan orogenic belts in India, coupled with their corresponding blocking temperatures for various radiometric clocks in whole rocks and minerals, has been used to evaluate the cooling and the uplift histories of the respective orogenic belts. The blocking temperatures used in the present study of various Rb-Sr (isotopic homogenization at 600°C, muscovite at 500°C and biotite at 300°C), Pb-U (monazite at 530°C), K-Ar (muscovite at 350°C and biotite at 300°C) and fission-track clock (zircon at 350°C, sphene at 300°C, garnet at 280°C, muscovite at 130°C, hornblende at 120°C and apatite at 100°C for the cooling rate l°C/Ma) have been found suitable to explain the differences in mineral ages by different radiometric techniques. The nature of the cooling curves drawn using the temperature versus age data for various orogenic cycles in India has also been discussed. The cooling and the uplift patterns determined for various orogenic cycles of India, suggest comparatively slow cooling (5.0–0.2°C/Ma) and uplift (180–2 m/Ma) for the Peninsular regions and rapid cooling (25.0–1.0° C/Ma) and fast uplift (800–30 m/Ma) during the Himalayan Orogenic Cycle (Upper Cretaceous—Tertiary) in the Extra-Peninsular region.     

A comparative evaluation of groundwater suitability for irrigation and drinking purposes in two intensively cultivated districts of Punjab, India

Punjab is the most cultivated state in India with the highest consumption of fertilizers. Patiala and Muktsar districts are two agricultural dominated districts of Punjab located in extreme south-east and south-west of the state. This paper highlights temporal variations of the groundwater quality and compares its suitability for irrigation and drinking purpose in these two districts. Water samples were collected in March and September 2003, representing the pre-monsoon and post-monsoon seasons, respectively. Water samples were analysed for almost all major cations, anions, dissolved heavy metals and turbidity. Parameters like sodium adsorption ratio, % sodium, residual sodium carbonate, total hardness, potential salinity, Kelley’s ratio, magnesium ratio, index of base exchange and permeability index were calculated on the basis of chemical data. A questionnaire was also used to investigate perception of villagers on taste and odour. Comparison of the concentration of the chemical constituents with WHO (world health organization) drinking water standards of 2004 and various classifications show that present status of groundwater in Patiala is better for irrigation and drinking purposes except for a few locations with a caution that it may deteriorate in near future. In Muktsar, groundwater is not suitable for drinking. Higher total hardness (TH) and total dissolved solids at numerous places indicate the unsuitability of groundwater for drinking and irrigation. Results obtained in this forms baseline data for the utility of groundwater. In terms of monsoon impact, Patiala groundwater shows dilution and flushing but Muktsar samples show excessive leaching of different chemical components into the groundwater leading to the enrichment of different anions and cations indicating pollution from extraneous sources. No clear correlation between the quality parameters studied here and perceived quality in terms of satisfactory taste response were obtained at electrical conductivity values higher than the threshold minimum acceptable value.     

Morphostratigraphy and palaeoclimate appraisal of the Leh valley,Ladakh Himalayas,India

In the present paper we study morphology, occurrence and mutual interrelationship of erosional (amphitheaters) and depositional landforms belonging to glacial (moraines), fluvio-glacial (glacial out wash), mass wasting (alluvial fans), aeolian (obstacle dune and sand sheets) and lacustrine (palaeo-lake sediments) processes within the Leh valley. These landforms are the geomorphic expression of past deglaciation grouped into five Formative Stages of Landform (FSL 1 to FSL 5) development in the Leh valley. The broad age bracket for the formative stages are based on the empirical relationship of the landforms, available chronology and their correlation with comparable climate phases. The retreat of glaciers in the Leh valley, along the southern slopes of Ladakh hill range and their retention over the northern slopes and Karakoram is further explained.     

Attenuation of coda waves in the Nubra-Siachen region,Himalaya, India

The attenuation properties have been estimated in the Nubra-Siachen region situated in the highly mountainous region of Himalayan belt. Coda wave quality factor (Q_c) has been determined for this virgin region by using the single backscattering method. A total of thirty earthquakes recorded in this region, which fall in the epicentral distance range of 3 to 115km have been used for the present work. A 30 sec window length of coda waves at different central frequencies 1.5, 3.0, 6.0, 9.0, 12.0, 18.0 and 24.0 Hz have been studied to determine Q_c at different recording stations. The frequency dependent coda wave quality factor relationships of the form Q_c(f) = Q_ofⁿ, have been computed at each recording stations separately: BASE: Q_c(f) = (137 ± 4.2) f^{(0.99 ± 0.12)}, CHALUNKA: Q_c(f) = (116±3.8)f^(1.0±0.05), PARTA: Q_c(f) = (122±3.0)f^(1.0±0.02), and SASOMA: Q_c(f) = (111±4.1)f^(1.0±0.03). A regional Q_c relation has been developed for the Nubra-Siachen region by using the average value of Q_c at different frequencies obtained at each recording station of the form Q_c(f) = (121±7.2)f^(1.0±0.04). The average Q_c values vary from 183 at 1.5 Hz to 3684 at 24 Hz central frequencies. The present regional relation developed for Nubra-Siachen region indicates heterogeneous and tectonically active region.     

Fission track annealing characteristics of garnet

Fission track annealing characteristics of almandine-spessartine garnet have been investigated. The data indicate that the activation energy for thermal fading of tracks ranges from 2.6 to 6.0 eV with a mean of 4.1 eV. The annealing temperatures for this variety are lower than for the andradite-grossular variety.