Drainage Analysis in a Part of the Brahmaputra Valley in Sivasagar District, Assam, India, to Detect the Role of Neotectonic Activity     

Sangeeta Sharma  Jogendra Nath Sarma 《Journal of the Indian Society of Remote Sensing》2013,41(4):895-904

An analysis of the drainage network of a part of Sivasagar district, Assam, India, is undertaken to reveal the role of neotectonic activity of the area. A number of fluvial geomorphic anomalies have been identified in the area. A prominent annular drainage anomaly is displayed by the major rivers—the Dikhu, Jhanzi, Namdang, Dorika and Disang, whose courses are carved in response to the ongoing tectonic deformation in the area. This study reveals that the development of topography and drainage system of the study area have been influenced by active subsurface geological structures. Formation of paleochannels, compressed meanders, reticulate streams, swamps, sagging of grounds, stream alignments, lineaments, knick points and abandonment of rivers as well as development of smaller drainage anomalies also substantiate the active nature of the subsurface structures.  相似文献   

Assessment of Seismic Site Conditions: a Case Study from Guwahati City,Northeast India     

S. K. Nath  K. K. S. Thingbaijam 《Pure and Applied Geophysics》2011,168(10):1645-1668

The 1897 Great Shillong earthquake revealed considerable seismic susceptibility in Guwahati City, such as soil liquefaction, landslides, and surface fissures. In an attempt to quantify the seismic vulnerability of the city based on geological, seismological, and geotechnical aspects concerning seismic site characterization, in-depth analysis was performed using a microtremor survey with recordings of five small to moderate magnitude (4.8 ≤ m_b ≤ 5.4) earthquakes that occurred in 2006 and geotechnical investigations using the Standard Penetration Test (SPT). Additionally, the basement topography was established using vertical electrical resistivity sounding and selected drill-hole information. Region-specific relationships are derived by correlating the estimated values of predominant frequency, shear-wave velocity, and basement depth indicating conformity with the predominant frequency distribution and the basin topography underlain by a hard granitic basement. Most parts of the city adhere to the predominant frequency range of 0.5–3.5 Hz, setting aside areas of deep sediment fills or hilly tracts, suggesting that the existing moderate-rise RC buildings in the territory are seismically vulnerable. Furthermore, the geotechnical assessment of the soil liquefaction potential reveals widespread susceptibility across the terrain. Eventually, a site classification map of the city is prepared following the National Earthquake Hazard Program (NEHRP) provision. The average site amplification factor from geotechnical modeling for site class D is about 3 in the frequency range of 2–4 Hz. In addition, earthquake data yield an average site amplification factor of 4–6 in the frequency range of 1.2–5.0 Hz at the seismic stations located in site class E and F. High site amplifications of around 5.5 and 7.5 at 2 Hz, respectively, are observed at AMTRON and IRRIG seismic stations, which are located in the proximity of Precambrian rocks, indicating probable basin edge effects—scattering and diffraction of incident energy. Interplay of dispersed valleys surrounded by small hillocks in the study region is likely to induce micro-basin effects where the sediment thickness/depth vis-à-vis predominant frequency and basin geometry in conjunction play pivotal roles in the augmentation of site response.  相似文献   

Radon emanation of heterogeneous basin deposits in Kathmandu Valley,Nepal     

Frédéric Girault  Ananta Prasad Gajurel  Frédéric Perrier  Bishal Nath Upreti  Patrick Richon 《Journal of Asian Earth Sciences》2011,40(2):595-610

Effective radium-226 concentration (EC_Ra) has been measured in soil samples from seven horizontal and vertical profiles of terrace scarps in the northern part of Kathmandu Valley, Nepal. The samples belong to the Thimi, Gokarna, and Tokha Formations, dated from 50 to 14 ky BP, and represent a diverse fluvio-deltaic sedimentary facies mainly consisting of gravelly to coarse sands, black, orange and brown clays. EC_Ra was measured in the laboratory by radon-222 emanation. The samples (n = 177) are placed in air-tight glass containers, from which, after an accumulation time varying from 3 to 18 days, the concentration of radon-222, radioactive decay product of radium-226 and radioactive gas with a half-life of 3.8 days, is measured using scintillation flasks. The EC_Ra values from the seven different profiles of the terrace deposits vary from 0.4 to 43 Bq kg^?1, with profile averages ranging from 12 ± 1 to 27 ± 2 Bq kg^?1. The values have a remarkable consistency along a particular horizon of sediment layers, clearly demonstrating that these values can be used for long distance correlations of the sediment horizons. Widely separated sediment profiles, representing similar stratigraphic positions, exhibit consistent EC_Ra values in corresponding stratigraphic sediment layers. EC_Ra measurements therefore appear particularly useful for lithologic and stratigraphic discriminations. For comparison, EC_Ra values of soils from different localities having various sources of origin were also obtained: 9.2 ± 0.4 Bq kg^?1 in soils of Syabru–Bensi (Central Nepal), 23 ± 1 Bq kg^?1 in red residual soils of the Bhattar-Trisuli Bazar terrace (North of Kathmandu), 17.1 ± 0.3 Bq kg^?1 in red residual soils of terrace of Kalikasthan (North of Trisuli Bazar) and 10 ± 1 Bq kg^?1 in red residual soils of a site near Nagarkot (East of Kathmandu). The knowledge of EC_Ra values for these various soils is important for modelling radon exhalation at the ground surface, in particular in the vicinity of active faults. Importantly, the study also reveals that, above numerous sediments of Kathmandu Valley, radon concentration in dwellings can potentially exceed the level of 300 Bq m^?3 for residential areas; a fact that should be seriously taken into account by the governmental and non-governmental agencies as well as building authorities.  相似文献   

Analysis of a genesis potential parameter during pre-cyclone watch period over the Bay of Bengal     

Sankar Nath  S. D. Kotal  P. K. Kundu 《Natural Hazards》2013,65(3):2253-2265

The genesis potential parameter (GPP) consists of two dynamical variables low-level relative vorticity and vertical wind shear, and two thermodynamic variables middle tropospheric relative humidity and instability are analysed during pre-cyclone watch period over the Bay of Bengal. The pre-cyclone watch period is taken as the period prior to 72-h from the formation of a Depression. The GPP values for 30 tropical disturbances that formed over the Bay of Bengal during the period 2001–2010 are analysed. An independent evaluation of the parameter and possible applications to operational forecasting are presented using data from the year 1998 to 1999. The variables of GPP are calculated using the ECMWF interim reanalysis 1.5° × 1.5° resolution data, averaged within an area of 5° × 5° box on the centre of tropical disturbances and also over the 5° × 5° boxes over the adjacent surrounding areas. The results show that maximum value is observed over the genesis region at 48- and 24-h lead time for both the cases of cyclones and Depressions. The threshold value of GPP is found to be 9.3, 6.3 and 2.7 during pre-cyclone watch period at 24-, 48- and 72-h lead time, respectively. A distinction in GPP values above threshold value for cyclonic and a Depression system is also observed for the cyclogenesis region in 69, 75 and 75 % of cases at 72-, 48- and 24-h lead time, respectively. However, the individual case studies show that the GPP could indicate the genesis of a tropical cyclone with a 2-day lead time. The mean GPP values are 11.8, 8.5 and 3.8 for cyclonic systems and 6.9, 4.2 and 1.6 for Depression systems over an area of a box 5° × 5° on the systems at 24-, 48- and 72-h lead time, respectively, from the stage of Depression. The result of the study is found to be providing probable area of genesis and intensification of a tropical disturbance at a 2 day lead time from the stage Depression.  相似文献   

Practices of participation in coastal area management: Experience from Kenya     

Hom Nath Gartaula   《Ocean & Coastal Management》2008,51(7):528-535

This paper explores a development intervention, discourses involved and people's encounter at the interfaces during interaction and negotiation processes in everyday project life. It aims to get insight in the participatory intervention; how participatory is it and what is the intention behind the concept? This ethnography of an ongoing program in Kenya concludes that creation of participatory projects is a strategy of development practitioners to have high-rated evaluation of the project for donor funding but, in practice, the concept of participation is used by actors according to their interest and need.  相似文献   

Late Quaternary record of Indian summer monsoon-induced stratification and productivity collapse in the Andaman Sea     

A. V. Sijinkumar  B. Nagender Nath  Steven Clemens  N. M. Gayathri  P. Miriyala 《第四纪科学杂志》2021,36(2):298-310

During each summer monsoon, the northeastern Indian Ocean receives a huge amount of rain and river discharge, resulting in strong stratification and prevalence of oligotrophic conditions. These water column changes impact upper ocean productivity which is reflected in the planktonic foraminifera distribution, providing an opportunity to study the effect of monsoon forcing and stratification history. Analogous to modern-day stratification, very intense water column stratification and productivity collapse were observed associated with Indian summer monsoon (ISM) evolution. This paper reports significant stratification events during MIS 3 (37.0 to 33 and 27 to 24 cal ka), Bølling/Allerød (B/A), early Holocene (10.0 to 8.0 cal ka) and mid-Holocene (7.0 to 5.0 cal ka) which slowly muted upwelling and productivity. The deglacial intensification of the ISM started in the early stages of the Bølling/Allerød (B/A) followed by slight weakening during the Younger Dryas and regained strength during the early Holocene, coinciding with the highest summer insolation at 30°N. A progressive decline in the abundances of productivity and salinity proxies from 4.2 to 2.0 cal ka suggests a gradual weakening of the ISM. The late Quaternary productivity variations in the Bay of Bengal and the Andaman Sea are primarily controlled by salinity-related stratification.  相似文献   

Self-similar flow behind a spherical shock with varying strength in an inhomogeneous medium     

Onkar Nath 《Astrophysics and Space Science》1988,146(1):169-174

The model of self-similar shock wave produced on account of an instantaneous release of energy in a non-uniform gaseous mass, has been discussed with the equilibrium conditions. The disturbance are headed by a shock of variable strength. This model is of considerable physical interest in sonic booms, phenomena associated with laser production of plasma, high altitude nuclear detonation, supernova explosion and sudden expansion of corona into the interplanetary space.  相似文献   

Thermal and mass diffusion on MHD natural convective flow of a rarefied gas along vertical porous plate     

P. C. Ram  R. Nath  A. K. Agrawal 《Astrophysics and Space Science》1984,98(1):81-99

The flow of an electrically conducting incompressible rarefied gas due to the combined buoyancy effects of thermal and mass diffusion past an infinite vertical porous plate with constant suction has been studied in the presence of uniform transverse magnetic field. The problem has been solved for velocity, temperature, and concentration fields. It has been observed that mean velocity and the mean temperature are affected by the Grashof numbersG ₁ andG ₂, the slip parameterh ₁, temperature jump coefficienth ₂, concentration jump coefficienth ₃ and magnetic field parameterM. The amplitude and the phase of skin-friction and the rate of heat transfer are affected by frequency in addition to the above parameters. They are shown graphically. The numerical values of the mean skin-friction and the mean rate of heat transfer are also tabulated.  相似文献   

Mobility of arsenic in West Bengal aquifers conducting low and high groundwater arsenic. Part I: Comparative hydrochemical and hydrogeological characteristics     

Bibhash Nath  Doris Stüben  Sukumar Basu Mallik  Debashis Chatterjee  Laurent Charlet 《Applied Geochemistry》2008

The present study demonstrates the importance of hydrogeochemical characteristics (groundwater flow and recharge) of an aquifer in the release of As to groundwater. The study area (∼20 km²) is located in Chakdaha block, Nadia district, West Bengal, which hosts groundwaters of variable As content. The spatial distribution pattern of As is patchy with areas containing groundwater that is high in As (>200 μg L⁻¹) found in close vicinity to low As (<50 μg L⁻¹) groundwaters (within 100 m). The concentration of groundwater As is found to decrease with depth. In addition, the data shows that there is no conspicuous relationship between high groundwater As concentration and high groundwater abstraction, although the central cone of depression has enlarged over 2 a and is extending towards the SE of the study area. The river Hooghly, which forms the NW boundary of the study site, shows dual behaviour (effluent and influent during pre- and post-monsoon periods, respectively), complicating the site hydrogeology. The observed groundwater flow lines tend to be deflected away from the high As portion of the aquifer, indicating that groundwater movement is very sluggish in the As-rich area. This leads to a high residence time for this groundwater package, prolonging sediment–water interaction, and hence facilitating groundwater As release.  相似文献   

Fog forecasting using rule-based fuzzy inference system     

A. K. Mitra  Sankar Nath  A. K. Sharma 《Journal of the Indian Society of Remote Sensing》2008,36(3):243-253

Operational meteorology is perceived as a fuzzy environment in which information is vaguely defined. The mesoscale processes such as fog, stratus and convection are generally dependent on the topography of the place and has always been difficult to forecast for the meteorologists. The main objective of the present study is to introduce the concept of fuzzy inference system (FIS) in the prediction of fog. This approach uses the concept of a pure fuzzy logic system where the fuzzy rule base consists of a collection of fuzzy IF-THEN rules. The fuzzy inference engine uses these fuzzy IF-THEN rules to determine a mapping from fuzzy sets in the input universe of discourse to fuzzy sets in the output universe of discourse based on fuzzy logic principles. Basic weather elements, which affect weather characteristics of fog, are fuzzified. These are then used in fuzzy weather prediction models based on fuzzy inferences. These models are simulated and the crisp results obtained using developed defuzzification strategies are compared with the actual weather data. The basis of methodology is to construct the fuzzy rule base domain from the available daily current weather observations in winter season over New Delhi. The results reveal that dew point spread and rate of change of dew point spread are the most important parameters for the formation of fog. The results further indicate that fog formation over New Delhi are dominant when (i) dew point is greater then 7°C along with dew point spread between 1 and 3°C. (ii) rate of change of dew point spread must be negative and wind speed should be less than 4 knots. This study presents a technique for predicting the probability of fog over New Delhi for 5–6 hours in advance. The skill score indicates that the performance of FIS is appreciably good. The method is found to be promising for operational application.  相似文献