Structural and metamorphic evolution of the rocks of the Jutogh Group, Chur half-klippe, Himachal Himalayas: A summary and comparison with the Simla area     

Dilip K. Mukhopadhyay  Tamal K. Ghosh  Bidyut K. Bhadra  Deepak C. Srivastava 《Journal of Earth System Science》1997,106(4):197-207

The rocks of the Jutogh Group in the Himachal Himalayas and their equivalents elsewhere are now considered to represent a several km thick crustal scale ductile shear zone, the so called Main Central Thrust Zone. In this article we present a summary of structural and metamorphic evolution of the Jutogh Group of rocks in the Chur half-klippe and compare our results with those of Naha and Ray (1972) who worked in the adjacent Simla klippe. The deformational history of the Jutogh Group of rocks in the area around the Chur-peak, as deduced from small-scale structures, can be segmented into: (1) an early event giving rise to two sets of very tight to isoclinal and coaxial folds with gentle dip of axial planes and easterly or westerly trend of axes, (2) an event of superimposed progressive ductile shearing during which a plethora of small-scale structures have developed which includes successive generations of strongly non-cylindrical folds, several generations of mylonitic foliation, extensional structures and late-stage small-scale thrusts, and (3) a last stage deformation during which a set of open and upright folds developed, but these are regionally unimportant. The structure in the largest scale (tens of km) can be best described in terms of stacked up thin thrust sheets. Km-scale asymmetric recumbent folds with strongly non-cylindrical hinge lines, developed as a consequence of ductile shearing, are present in one of these thrust sheets. The ductile shearing, large-scale folding and thrusting can be related to the development of the Main Central Thrust Zone. The microstructural relations show that the main phase of regional low-to medium-grade metamorphism (T ≈ 430–600°C andP ≈ 4.5–8.5 kbar) is pre-kinematic with respect to the formation of the Main Central Thrust Zone. Growth zoned garnets with typical bell-shaped Mn profiles and compensating bowl-shaped Fe profiles are compatible with this phase of metamorphism. Some of the larger garnet grains, however, show flat compositional profiles; if they represent homogenization of growth zoning, it would be a possible evidence of a relict high-grade metamorphism. The ductile shearing was accompanied by a low-greenschist facies metamorphism during which mainly chlorite and occasionally biotite porphyroblasts crystallized.  相似文献   

On selection and scaling of ground motions for analysis of seismically isolated structures     

Deepak R. Pant  Manika Maharjan 《地震工程与工程振动(英文版)》2016,15(4):633-648

A broader consensus on the number of ground motions to be used and the method of scaling to be adopted for nonlinear response history analysis (RHA) of structures is yet to be reached. Therefore, in this study, the effects of selection and scaling of ground motions on the response of seismically isolated structures, which are routinely designed using nonlinear RHA, are investigated. For this purpose, isolation systems with a range of properties subjected to bidirectional excitation are considered. Benchmark response of the isolation systems is established using large sets of unscaled ground motions systematically categorized into pulse-like, non-pulse-like, and mixed set of motions. Different subsets of seven to 14 ground motions are selected from these large sets using (a) random selection and (b) selection based on the best match of the shape of the response spectrum of ground motions to the target spectrum. Consequences of weighted scaling (also commonly referred to as amplitude scaling or linear scaling) as well as spectral matching are investigated. The ground motion selection and scaling procedures are evaluated from the viewpoint of their accuracy, efficiency, and consistency in predicting the benchmark response. It is confirmed that seven time histories are sufficient for a reliable prediction of isolation system displacement demands, for all ground motion subsets, selection and scaling procedures, and isolation systems considered. If ground motions are selected based on their best match to the shape of the target response spectrum (which should be preferred over randomly selected motions), weighted scaling should be used if pulse-like motions are considered, either of weighted scaling or spectral matching can be used if non-pulse-like motions are considered, and an average of responses from weighted-scaled and spectrum-matched ground motions should be used for a mixed set of motions. On the other hand, the importance of randomly selected motions in representing inherent variability of response is recognized and it is found that weighted scaling is more appropriate for such motions.  相似文献   

Uncertainty of soil erosion modelling using open source high resolution and aggregated DEMs     

Arun Mondal  Deepak Khare  Sananda Kundu  Sandip Mukherjee  Anirban Mukhopadhyay  Surajit Mondal 《地学前缘(英文版)》2017,8(3):425-436

Digital Elevation Model (DEM) is one of the important parameters for soil erosion assessment. Notable uncertainties are observed in this study while using three high resolution open source DEMs. The Revised Universal Soil Loss Equation (RUSLE) model has been applied to analysis the assessment of soil erosion uncertainty using open source DEMs (SRTM, ASTER and CARTOSAT) and their increasing grid space (pixel size) from the actual. The study area is a part of the Narmada river basin in Madhya Pradesh state, which is located in the central part of India and the area covered 20,558 km². The actual resolution of DEMs is 30 m and their increasing grid spaces are taken as 90, 150, 210, 270 and 330 m for this study. Vertical accuracy of DEMs has been assessed using actual heights of the sample points that have been taken considering planimetric survey based map (toposheet). Elevations of DEMs are converted to the same vertical datum from WGS 84 to MSL (Mean Sea Level), before the accuracy assessment and modelling. Results indicate that the accuracy of the SRTM DEM with the RMSE of 13.31, 14.51, and 18.19 m in 30, 150 and 330 m resolution respectively, is better than the ASTER and the CARTOSAT DEMs. When the grid space of the DEMs increases, the accuracy of the elevation and calculated soil erosion decreases. This study presents a potential uncertainty introduced by open source high resolution DEMs in the accuracy of the soil erosion assessment models. The research provides an analysis of errors in selecting DEMs using the original and increased grid space for soil erosion modelling.  相似文献   

    

Earle B. Amey 《Natural Resources Research》1996,5(4):195

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Model selection in Bayesian framework to identify the best WorldView-2 based vegetation index in predicting green biomass of salt marshes in the northern Gulf of Mexico     

Wei Wu  Matthew Bethel  Deepak R. Mishra  Tyler Hardy 《地理信息系统科学与遥感》2018,55(6):880-904

Coastal wetlands are among the most productive ecosystems globally but have experienced dramatic degradation and loss within the past several decades. Vegetation biomass of coastal wetlands is not only the key component of blue carbon storage but also plays an important role in vertical accretion, important for maintaining these habitats under relative sea-level rise. Remote sensing offers a cost-effective approach to study vegetation biomass at a broad spatial scale. We developed statistical models to predict peak aboveground green biomass of Spartina alterniflora and Juncus roemerianus, two dominant species of salt marshes using WorldView-2 satellite imagery at the Grand Bay National Estuarine Research Reserve (NERR) on the Mississippi coast in the northern Gulf of Mexico. The model accounted for nested data structures in the sampled biomass, assimilated uncertainties from data, parameters and model structures, and helped determine the best vegetation index among a variety of commonly-used indices to predict aboveground green biomass. We developed a series of mixed-effects models, which included different combinations of fixed effect(s), random intercept, and random slope(s). The fixed effects were species and one of the 60 vegetation indices derived from a WorldView-2 image obtained on 6 October 2012. The random effect used was site. We implemented the models in a Bayesian framework and selected the best model structure and vegetation index based on minimum posterior predictive loss and deviance information criterion. The results showed that the best vegetation index to predict peak green biomass was the green chlorophyll index derived from the reflectance values of band 8 (near-infrared) and band 3 (green), and its effect on biomass prediction varied among sites. The inclusion of species as a fixed effect improved the model prediction. The study demonstrated the need to account for spatial dependence of data in developing a robust model, and the importance of the second WorldView-2 near-infrared band (860–1040 nm) in predicting aboveground green biomass for the Grand Bay NERR. The analysis using mixed-effects modeling in Bayesian inference which coherently combined field and WorldView-2 data with uncertainties accounted for provides a robust and nondestructive tool for resource managers to monitor the status of coastal wetlands at a high spatial resolution in a timely manner. Through this study, we hope to emphasize the importance of appropriately accounting for nested data structures using mixed-effects models and promote wider application of Bayesian inference to facilitate assimilation of uncertainties in remote sensing applications.  相似文献   

Precipitable water vapor estimation in India from GPS-derived zenith delays using radiosonde data   总被引：1，自引：0，他引：1  

Dinesh Singh  Jayanta Kumar Ghosh  Deepak Kashyap 《Meteorology and Atmospheric Physics》2014,123(3-4):209-220

One of the most recent applications of global positioning system (GPS) is the estimation of precipitable water vapor (PWV). It requires proper modeling to extract PWV from zenith wet delay (ZWD). The existing global models take no account of latitudinal and seasonal variation of meteorological parameters in the atmosphere. In fact, they ignore the atmospheric conditions at a specific location. Therefore, site-specific PWV models have been developed for five stations spread over the Indian subcontinent, using 3-year (2006–2008) radiosonde data from each of these stations. Furthermore, a similar regional PWV model is also developed for the Indian region. The purpose of the developed site-specific as well as regional model was to convert ZWDs into PWV without using surface meteorological parameters. It has been found that the developed regional and site-specific PWV models show about mm-level accuracy in estimating PWV using derived ZWD from radiosonde as input. The developed site-specific, regional models were also used to extract PWV from GPS-derived ZWD at Bangalore and New Delhi. The accuracy of the developed site-specific and regional model is of the same level. The PWV accuracy obtained with the developed regional model is about 6.28, 6.6 mm in comparison to radiosonde PWV at Bangalore and New Delhi, respectively.  相似文献   

Assessment of Chock Capacity and Strata Caving for a Longwall Mine     

Manoj Khanal  Deepak Adhikary  Rao Balusu 《Geotechnical and Geological Engineering》2012,30(2):395-405

A mine scale numerical analysis of modern day longwall using a 3D Cosserat continuum method has been presented. The effect of mine specific geological conditions on viability of introducing a modern day longwall is comprehensively investigated and analysed in this paper. The various longwall parameters like chock (face support) convergence and strata caving mechanism are evaluated. The varying thickness of the sandstone present in the roof can be seen to have a strong impact on the magnitude and pattern of chock convergence. The paper also discusses the performance of chocks with different capacities under identical conditions. The effect of overlaying sandstone properties and width of the longwall panels have also been investigated. The analyses carried out in this study is expected to provide valuable process guidance during the mine design in relation to selecting the optimal mine geometry and support capacity so that the potential mining hazards could be minimized.  相似文献   

A new ensemble-based data assimilation algorithm to improve track prediction of tropical cyclones     

Deepak Subramani  R. Chandrasekar  K. Srinivasa Ramanujam  C. Balaji 《Natural Hazards》2014,71(1):659-682

This paper proposes a new ensemble-based algorithm that assimilates the vertical rain structure retrieved from microwave radiometer and radar measurements in a regional weather forecast model, by employing a Bayesian framework. The goal of the study is to evaluate the capability of the proposed technique to improve track prediction of tropical cyclones that originate in the North Indian Ocean. For this purpose, the tropical cyclone Jal has been analyzed by the community mesoscale weather model, weather research and forecasting (WRF). The ensembles of prognostic variables such as perturbation potential temperature (θ, k), perturbation geopotential (?, m²/s²), meridional (U) and zonal velocities (V) and water vapor mixing ratio (q _v , kg/kg) are generated by the empirical orthogonal function technique. An over pass of the tropical rainfall-measuring mission (TRMM) satellite occurred on 06th NOV 0730 UTC over the system, and the observations from the radiometer and radar on board the satellite(1B11 data products) are inverted using a combined in-home radiometer-radar retrieval technique to estimate the vertical rain structure, namely the cloud liquid water, cloud ice, precipitation water and precipitation ice. Each ensemble is input as a possible set of initial conditions to the WRF model from 00 UTC which was marched in time till 06th NOV 0730 UTC. The above-mentioned hydrometeors from the cloud water and rain water mixing ratios are then estimated for all the ensembles. The Bayesian filter framework technique is then used to determine the conditional probabilities of all the candidates in the ensemble by comparing the retrieved hydrometeors through measured TRMM radiances with the model simulated hydrometeors. Based on the posterior probability density function, the initial conditions at 06 00 UTC are then corrected using a linear weighted average of initial ensembles for the all prognostic variables. With these weighted average initial conditions, the WRF model has been run up to 08th Nov 06 UTC and the predictions are then compared with observations and the control run. An ensemble independence study was conducted on the basis of which, an optimum of 25 ensembles is arrived at. With the optimum ensemble size, the sensitivity of prognostic variables was also analyzed. The model simulated track when compared with that obtained with the corrected set of initial conditions gives better results than the control run. The algorithm can improve track prediction up to 35 % for a 24 h forecast and up to 12 % for a 54 h forecast.  相似文献   

Evaluating Hyperspectral Imager for the Coastal Ocean (HICO) data for seagrass mapping in Indian River Lagoon,FL     

Hyun Jung Cho  Igor Ogashawara  Deepak Mishra  Joseph White  Andrew Kamerosky  Lori Morris 《地理信息系统科学与遥感》2014,51(2):120-138

Differentiation between benthic habitats, particularly seagrass and macroalgae, using satellite data is complicated because of water column effects plus the presence of chlorophyll-a in both seagrass and algae that result in similar spectral patterns. Hyperspectral imager for the coastal ocean data over the Indian River Lagoon, Florida, USA, was used to develop two benthic classification models, Slope_RED and Slope_NIR. Their performance was compared with iterative self-organizing data analysis technique and spectral angle mapping classification methods. The slope models provided greater overall accuracies (63–64%) and were able to distinguish between seagrass and macroalgae substrates more accurately compared to the results obtained using the other classifications methods.  相似文献