Basement configuration of the Jhagadia–Rajpipla profile in the western part of Deccan syneclise,India from travel-time inversion of seismic refraction and wide-angle reflection data     

A.S.N. Murty  P. Koteswara Rao  M.M. Dixit  G. Kesava Rao  M.S. Reddy  B.R. Prasad  D. Sarkar 《Journal of Asian Earth Sciences》2011,40(1):40-51

2-D velocity structure up to the basement is derived by travel-time inversion of the first arrival seismic refraction and wide-angle reflection data along the SW–NE trending Jhagadia–Rajpipla profile, located on the western part of Deccan syneclise in the Narmada–Tapti region. The study region is mostly covered by alluvium. Inversion of refraction and wide-angle reflection data reveals four layered velocity structure above the basement. The first two layers with P-wave velocities of 1.95–2.3 km s^?1 and 2.7–3.05 km s^?1 represent the Recent and Quaternary sediments respectively. The thickness of these sediments varies from 0.15 km to 3.4 km. The third layer with a P-wave velocity of 4.8–5.1 km s^?1 corresponds to the Deccan volcanics, whose thickness varies from 0.5 km to 1.0 km. Presence of a low velocity zone (LVZ) below the high velocity volcanic rocks in the study area is inferred from the travel-time ‘skip’ and amplitude decay of the first arrival refraction data and the wide-angle reflection from top of the LVZ present immediately after the first arrival refraction from Deccan Trap layer. The thickness of the low velocity Mesozoic sediments varies from 0.3 km to 1.7 km. The basement with a P-wave velocity of 5.9–6.15 km s^?1 lies at a depth of 4.9 km near Jhagadia and shallows to 1.2 km towards northeast near Rajpipla. The results indicate presence of low velocity Mesozoic sediments hidden below the Deccan Trap layer in the western part of the Deccan syneclise.  相似文献   

Oxygen isotope analysis of multiple,single ostracod valves as a proxy for combined variability in seasonal temperature and lake water oxygen isotopes   总被引：1，自引：0，他引：1  

Yama Dixit  David A. Hodell  Rajiv Sinha  Cameron A. Petrie 《Journal of Paleolimnology》2015,53(1):35-45

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Deep seismic soundings along Hirapur-Mandla profile, central India   总被引：1，自引：0，他引：1  

K.L. Kaila  P.R.K. Murty  D.M. Mall  M.M. Dixit  D. Sarkar 《Geophysical Journal International》1987,89(1):399-404

Summary. The crustal depth section along Hirapur-Mandla profile has been computed in two steps from Deep Seismic Sounding (DSS) data. The shallow section up to the crystalline basement is derived by inverting first arrival refraction travel times. The upper Vindhyan sediments (velocity 4.5 km s⁻¹) have a maximum thickness of about 1.5 km at Bakshaho. The lower Vindhyan sediments (velocity 5.4 km s⁻¹) were deposited north of Narmada-Son lineament between Katangi and Narsinghgarh in a graben developed in crystalline basement. The thickness of the lower Vindhyans increases from north to south towards Katangi and the depth to the basement reaches 5.5 km near Jabera. The depth to the Moho boundary varies from 39.5 km near Tikaria to 45 km at Narsinghgarh. The narrow block between Katangi and Jabalpur forms a horst feature which represents the Narmada-Son lineament forming the southern boundary of the Vindhyan basin. Two-dimensional ray tracing was performed generating travel time curves from various shot points which were matched with observed travel time data.  相似文献   

Initiatives for earthquake disaster risk management in the Kathmandu Valley     

Amod Mani Dixit  Ryuichi Yatabe  Ranjan Kumar Dahal  Netra Prakash Bhandary 《Natural Hazards》2013,69(1):631-654

Situated over the Himalayan tectonic zone, Kathmandu Valley as a lake in geological past has a long history of destructive earthquakes. In recent years, the earthquake risk of the valley has significantly increased due mainly to uncontrolled development, poor construction practices with no earthquake safety consideration, and lack of awareness among the general public and government authorities. Implementation of land use plan and building codes, strengthening of design and construction regulations, relocation of communities in risky areas, and conduction of public awareness programs are suitable means of earthquake disaster risk management practice. Kathmandu, the capital of Nepal, is still lacking earthquake disaster risk management plans. So, this paper highlights some initiatives adopted by both governmental and nongovernmental organizations of Nepal to manage earthquake disaster risk in the Kathmandu Valley. It provides some comprehensive information on recent initiatives of earthquake disaster risk management in the valley and also highlights the outcomes and challenges.  相似文献   

The effect of Coriolis force on acceleration covariance in MHD turbulent dusty flow with rotational symmetry     

T. Dixit  B. N. Upadhyay 《Astrophysics and Space Science》1989,153(2):257-268

In this paper we have considered MHD turbulent dusty flow of an incompressible, viscous fluid which is nearly isotropic with rotational and spatially homogeneous. The expression for acceleration covariance in the presence of Coriolis force has been derived and solution has been obtained in terms of defining scalars.  相似文献   

Floods and Vulnerability: Need to Rethink Flood Management     

Dixit  Ajaya 《Natural Hazards》2003,28(1):155-179

Responses to flooding in the Himalaya-Ganga region have conventionally beensought under the hierarchic mode using the strategy of control. Because it has notgiven due consideration to diverse contexts of the region and thereby the specificapproaches that such context necessitate, the particular approach has not broughtabout security from flooding. Three responses are seen in the terrain of flooddisaster. These are the hierarchic manager, individualistic innovator and theegalitarian social activist. The hierarchies define control as the solution to theproblems of flood: this is the approach preferred by state agencies. At theindividualistic level the sought strategy is flexibility to cope with the situation.The response by social activists is guided by egalitarian critiques of the hierarchicapproach. Each pursues his/her own styles and continuously contests the policyterrain. This paper reviews the nature of flood disaster in the Himalaya-Gangaby focussing on plains Nepal. It argues that conventional approach has not beenable to provide the security envisaged. The paper suggests that vulnerability ofpeople in risk-prone areas must be addressed by enhancing resilience capacity.For this to happen the approach must be pluralistic that gives space to eachmanagement style with varying obligations at varying scales.  相似文献   

Special issue on Flood Problems and Management in South Asia: Preface     

Monirul Qader Mirza  M.  Dixit  Ajaya  Nishat  Ainun 《Natural Hazards》2003,28(1):vii-ix

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The importance of model choice on pH inferences from scaled chrysophyte assemblages in North America     

Andrew M. Paterson  Brian F. Cumming  Sushil S. Dixit  John P. Smol 《Journal of Paleolimnology》2002,27(3):379-391

The selection of a reliable inference model is a crucial step in developing ecologically sound reconstructions of environmental variables in the past. We compared intra- and inter-regional regression-based models, and an inter-regional Modern Analogue Technique (MAT) model in their ability to infer lakewater pH from scaled chrysophyte assemblages. The performance of each model was assessed by examining cross-validated coefficients of determination and prediction errors, and through reconstructing the pH of 50 modern and fossil samples in south-central Ontario, Canada. Using the intra- and inter-regional data sets, we found little difference in the ability of the regression-based models to infer present-day pH. Partial Least Squares (PLS) regression, Weighted Averaging (WA), and Weighted Averaging Partial Least Squares (WA-PLS) inference models showed similar values for jack-knifed coefficients of determination (r² _jack), root mean squared errors of prediction (RMSEP_jack), and mean and maximum biases. Based on an analogue matching approach, the inferred values from 48 fossil sediment samples suggested that the intra-regional model did not provide reliable reconstructions for approximately half of the fossil samples. However, inferences from the inter-regional MAT and regression-based models were found to have appropriate analogues and thus considered to be more reliable.  相似文献   

Evening and morning twilight enhancement of λ5577 Å atomic oxygen line at Allahabad     

N. Shrivastava  S. Shrivastava  S. D. Dixit  A. N. Shrivastava 《Earth, Moon, and Planets》1989,44(2):181-190

A photometer for the observation of twilight airglow emissions has been fabricated. Intensity variation in morning and evening twilight of 5577 Å line of atomic oxygen has been recorded at Allahabad for one year duration from 23rd March, 1987 to 22nd March, 1988. The enhancement in the intensity of the line is found to be irregular. Out of 40 clear evenings and 25 clear mornings from 23rd March, 1987 to 15th June, 1987 enhancement is observed in 24 evenings and 15 mornings. However, no enhancement is observed during the period from 15th September, 1987 to 15th October, 1987. It is found that rise and fall of intensity is exponential during twilight period. Considering different mechanism for the excitation of atomic oxygen green line, it is concluded that none of them are able to explain enhancement. More work is needed to be carried out for the better understanding of the problem.  相似文献   

Acidification and metal contamination in Whitepine Lake (Sudbury,Canada): a paleolimnological perspective     

Aruna S. Dixit  Sushil S. Dixit  John P. Smol 《Journal of Paleolimnology》1993,9(2):141-146

Diatom and chrysophyte assemblages from a sediment core from Whitepine Lake were examined to infer changes in lakewater pH, nickel and aluminum concentrations since pre-industrial times, and to help determine the cause of the virtual extirpation of the lake trout population from the lake during the 1960s and 1970s. Our study indicates that acidification started in the 1920s, and that the maximum inferred pH decline (from 6.2 to 5.8) occurred between 1960 and 1970, coincident with the peak in metal mining and smelting activity in the Sudbury basin. Lakewater [Al] and [Ni], as inferred from our diatom transfer functions, increased. It appears that in addition to the pH decline, elevated [Al] may have played an important role in the decline of lake trout from Whitepine Lake in the 1960s and 1970s. Diatom-inferred lakewater pH and [Ni] have recovered slightly in the recent sediments, which coincides with reductions in emissions that have occurred since the mid-1970s.  相似文献