An efficient method of generating random permeability fields by the source point method     

Saleem G. Ghori  John P. Heller  Ashok K. Singh 《Mathematical Geology》1993,25(5):559-572

Aquifer properties, for example permeability and porosity, vary in space and may be characterized by their distributions. The property distribution is not totally random but shows some correlation structure. Because most of the values are not known, some rational method is required to generate credible aquifer distribution properties for inclusion in fluid transport models. This paper presents a numerically efficient method of generating geostatistical random fields, by the source Point Method (SPM). The SPM is a very efficient method and requires little computer time and relatively small data storage, as compared to other methods of generating random fields. In addition, the SPM is modified to include any desired amount of anisotropy in the property distribution of a system. By using conditional covariances, a formula for a two-dimensional anisotropic field is derived to prespecify the desired correlation length in any direction. Results show that for an anisotropic medium the correlation length can be pre-specified in any specific direction.  相似文献   

Dynamic response analysis of embankment dams     

Ashok K. Chugh 《国际地质力学数值与分析法杂志》1985,9(2):101-124

A one-dimensional wave propagation method for earthquake response analysis of horizontally-layered sites of infinite lateral extent is adapted to account for the finite cross-sectional dimensions of an embankment dam overlying a foundation deposit which may be considered infinite in its lateral extent. The procedure is used to study the response of an existing embankment dam for an actual earthquake record. A two-dimensional dynamic finite element analysis is also performed for this case. The records of ground acceleration at an outcropping base rock and at the crest of the dam are available for the site. The comparisons of computed and observed responses support the modified use of the simple numerical procedure.  相似文献   

Trend and persistence of precipitation under climate change scenarios for Kansabati basin,India     

Ashok K. Mishra  Mehmet Özger  Vijay P. Singh 《水文研究》2009,23(16):2345-2357

With increasing uncertainties associated with climate change, precipitation characteristics pattern are receiving much attention these days. This paper investigated the impact of climate change on precipitation in the Kansabati basin, India. Trend and persistence of projected precipitation based on annual, wet and dry periods were studied using global climate model (GCM) and scenario uncertainty. A downscaling method based on Bayesian neural network was applied to project precipitation generated from six GCMs using two scenarios (A2 and B2). The precipitation values for any of three time periods (dry, wet and annual) do not show significant increasing or decreasing trends during 2001–2050 time period. There is likely an increasing trend in precipitation for annual and wet periods during 2051–2100 based on A2 scenario and a decreasing trend in dry period precipitation based on B2 scenario. Persistence during dry period precipitation among stations varies drastically based on historical data with the highest persistence towards north‐west part of the basin. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Luminescence chronometry and geomorphic evidence of active fold growth along the Kachchh Mainland Fault (KMF), Kachchh, India: Seismotectonic implications   总被引：2，自引：0，他引：2  

George Mathew  Ashok K. Singhvi  Rama V. Karanth 《Tectonophysics》2006,422(1-4):71-87

The Kachchh region of Western India is a pericratonic basin experiencing periodic high magnitude earthquakes events. In 2001 a catastrophic seismic event occurred at Bhuj measuring M_w = 7.7. The epicenters of both the 1956 and 2001 earthquakes were along the Kachchh Mainland Fault (KMF), proximal to the eastern end of the Northern Hill Range (NHR). The latter is a topographic expression of an active fault related fold on the hanging wall, and is controlled by a south dipping blind thrust.The present study deals with the eastern sector of NHR and uses optical dating to reconstruct the chronology of tectonically caused incisions. Along the backlimb of the NHR, incision ages on, channel fills and valley fill terraces progressively decrease from  12 ka to 4.3 ka. This age progression along with geomorphic evidences (decrease in topographic relief, drainage capture and drainage migration across the fold nose) suggests an active vertical and lateral fold growth along the KMF. Optical ages suggest that during the Late Holocene, the average uplift rate along the eastern NHR was 10 ± 1 mm/a. Recent GPS based estimates on crustal shortening are  12 mm/a.The KMF and the South Wagad Fault (SWF) represent the bounding faults of a transtensional basin that formed during the initial rifting. This basin is termed as the Samakhiali basin. The compressive stresses on account of structural inversion from normal to reverse phase resulted in lobate-shaped anticlines along KMF and SWF zone. These anticlines subsequently coalesced and formed linked and overlap segments. The present study suggests that eastward lateral deformation across the eastern portion of KMF has continued and has now resulted in its interaction with a left step over transfer fault called the South Wagad Master Fault (SWMF). This implies an increasing transpersional deformation of the Samakhiali basin. We therefore, suggest that the eastward NHR ridge propagation along KMF resulted in the thrust faulting on the south dipping SWMF resulting in the Bhuj 2001 event. The increasing strain on this basin may cause enhanced seismicity in the future along the eastern KMF and Wagad region.  相似文献   

Demarcation of inland vessels’ limit off Mormugao port region,India: a pilot study for the safety of inland vessels using wave modelling     

P. Vethamony  V. M. Aboobacker  K. Sudheesh  M. T. Babu  K. Ashok Kumar 《Natural Hazards》2009,49(2):411-420

The Ministry of Shipping desires to revise the inland vessels’ limit (IVL) notification based on scientific rationale to improve the safety of vessels and onboard personnel. The Mormugao port region extending up to the Panaji was considered for this pilot study. Measured winds and wave parameters (AWS and moored buoy) as well as NCEP re-analysis and NCMRWF winds were used for the analysis and input to regional and local models. The results of wave model were validated with measured significant wave heights (SWHs) and the comparison shows a good match. The analysis indicates that SWHs do not exceed 2.0 m during non-monsoon months, and in monsoon months exceed 5.0 m, and even 7.0 m, especially during extreme events. In order to draw IVL contours for Goa coastal region, local model was set up and nearshore waves were simulated for the period May 2004–May 2005. Based on the nearshore SWH distribution, IVL contours have been fixed for the Mormugao port and Panaji coastal regions.  相似文献   

Changes in soil quality indicators under long-term sewage irrigation in a sub-tropical environment   总被引：3，自引：0，他引：3  

Reginald Ebhin Masto  Pramod K. Chhonkar  Dhyan Singh  Ashok K. Patra 《Environmental Geology》2009,56(6):1237-1243

Though irrigation with sewage water has potential benefits of meeting the water requirements, the sewage irrigation may mess up to harm the soil health. To assess the potential impacts of long-term sewage irrigation on soil health and to identify sensitive soil indicators, soil samples were collected from crop fields that have been irrigated with sewage water for more than 20 years. An adjacent rain-fed Leucaena leucocephala plantation system was used as a reference to compare the impact of sewage irrigation on soil qualities. Soils were analyzed for different physical, chemical, biological and biochemical parameters. Results have shown that use of sewage for irrigation improved the clay content to 18–22.7%, organic carbon to 0.51–0.86% and fertility status of soils. Build up in total N was up to 2,713 kg ha⁻¹, available N (397 kg ha⁻¹), available P (128 kg ha⁻¹), available K (524 kg ha⁻¹) and available S (65.5 kg ha⁻¹) in the surface (0.15 m) soil. Long-term sewage irrigation has also resulted a significant build-up of DTPA extractable Zn (314%), Cu (102%), Fe (715%), Mn (197.2), Cd (203%), Ni (1358%) and Pb (15.2%) when compared with the adjacent rain-fed reference soil. Soils irrigated with sewage exhibited a significant decrease in microbial biomass carbon (−78.2%), soil respiration (−82.3%), phosphatase activity (−59.12%) and dehydrogenase activity (−59.4%). An attempt was also made to identify the sensitive soil indicators under sewage irrigation, where microbial biomass carbon was singled out as the most sensitive indicator.  相似文献   

Near-infrared H- and K-band studies of the 2006 outburst of the recurrent nova RS Ophiuchi     

D. P. K. Banerjee  R. K. Das  N. M. Ashok 《Monthly notices of the Royal Astronomical Society》2009,399(1):357-368

We present near-infrared photospectroscopy in the H and K bands of the 2006 outburst of the recurrent nova RS Ophiuchi. The observations cover the period between 1 and 94 d after the eruption. The near-infrared light curve is presented. An extensive set of spectra is presented, lines identified and the general characteristics of the spectra discussed. Analysis of the H  i line profiles shows the presence of broad wings on both flanks of a strong central component indicating the presence of a bipolar velocity flow in the ejecta. Such a flow is kinematically consistent with the bipolar structure that the object displays in high-resolution spatial images. We discuss the behaviour and origin of the Fe  ii lines at 1.6872 and 1.7414 μm that are prominently seen throughout the span of the observations. It is examined and shown that Lyman α and Lyman continuum fluorescence are viable mechanisms to excite these lines. We draw upon the result, that collisional excitation can also contribute in exciting and significantly enhancing the strength of these Fe  ii lines, to propose that these lines originate from a site of high particle density. Such a likely site could be the high-density, low-temperature contact surface that should exists in the shock front in between the shocked ejecta and red giant wind. Recombination analysis of the H  i lines indicates deviations from case B conditions during most of the span of our observations indicating optical depth effects. It appears likely that the breakout of the shock front had not yet occurred till the end of our observations. An analysis is made of the temporal evolution of the [Si  vi ] 1.9641 μm coronal line and another coronal line at 2.0894 μm which is attributed to [Mn  xiv ]. Assuming collisional effects to dominate in the hot coronal gas, estimates are made of the ion temperature in the gas.  相似文献   

Crustal deformation rates in Assam Valley,Shillong Plateau,Eastern Himalaya,and Indo-Burmese region from 11 years (2002–2013) of GPS measurements     

Barman  Prakash  Jade  Sridevi  Shrungeshwara  T. S.  Kumar  Ashok  Bhattacharyya  Sanjeev  Ray  Jagat Dwipendra  Jagannathan  Saigeetha  Jamir  Wangshi Menla 《International Journal of Earth Sciences》2017,106(6):2025-2038

International Journal of Earth Sciences - The present study reports the contemporary deformation of the tectonically complex northeast India using 11 years (2002–2013) of GPS...  相似文献   

Evaluation of phase chemistry and petrochemical aspects of Samchampi-Samteran differentiated alkaline complex of Mikir Hills,northeastern India     

Abhishek Saha  Sohini Ganguly  Jyotisankar Ray  Nilanjan Chaterjee 《Journal of Earth System Science》2010,119(5):675-699

The Samchampi-Samteran alkaline complex occurs as a plug-like pluton within the Precambrian granite gneisses of Mikir Hills, Assam, northeastern India and it is genetically related to Sylhet Traps. The intrusive complex is marked by dominant development of syenite within which ijolitemelteigite suite of rocks is emplaced with an arcuate outcrop pattern. Inliers of alkali pyroxenite and alkali gabbro occur within this ijolite-melteigite suite of rocks. The pluton is also traversed by younger intrusives of nepheline syenite and carbonatite. Development of sporadic, lumpy magnetite ore bodies is also recorded within the pluton. Petrographic details of the constituent lithomembers of the pluton have been presented following standard nomenclatorial rules. Overall pyroxene compositions range from diopside to aegirine augite while alkali feldspars are typically orthoclase and plagioclase in syenite corresponds to oligoclase species. Phase chemistry of nepheline is suggestive of Na-rich alkaline character of the complex. Biotite compositions are typically restricted to a uniform compositional range and they belong to ‘biotite’ field in the relevant classification scheme. Garnets (developed in syenite and melteigite) typically tend to be Ti-rich andradite, which on a closer scan can be further designated as melanites. Opaque minerals mostly correspond to magnetite. Use of Lindsley’s pyroxene thermometric method suggests an equilibration temperature from ∼450°–600°C for melteigite/alkali gabbro and ∼400°C for syenite. Critical assessment of other thermometric methods reveals a temperature of equilibration of ∼700°–1350°C for ijolite-melteigite suite of rocks in contrast to a relatively lower equilibration temperature of ∼600°C for syenite. Geobarometric data based on pyroxene chemistry yield an equilibration pressure of 5.32–7.72 kb for ijolite, melteigite, alkali pyroxenite, alkali gabbro and nepheline syenite. The dominant syenite member of the intrusive plug records a much higher (∼11 kb) equilibration pressure indicating a deeper level of intrusion. Major oxide variations of constituent lithomembers with respect to differentiation index (D.I.) corroborate a normal magmatic differentiation. A prominent role of liquid immiscibility is envisaged from field geological, petrographic and petrochemical evidences. Tectonic discrimination diagrams involving clinopyroxene chemistry strongly suggest within plate alkaline affinity for the parental magma which is in conformity with the regional plume tectonics.  相似文献   

Textural characteristics,distribution pattern and provenance of heavy minerals in glacial sediments of Schirmacher Oasis,east Antarctica     

Ashok K. Srivastava  Pravin S. Ingle  Neloy Khare 《Journal of the Geological Society of India》2010,75(2):393-402

Heavy minerals of twenty sediment samples, belonging to polar ice sheet, lake, mainland area and shelf region of Schirmacher Oasis, east Antarctica, have been studied for their textural characteristics, abundance and provenance determination. The heavy crop is represented by zircon, tourmaline, rutile, garnet, hypersthene, hornblende, chlorite, enstatite, lawsonite, kyanite, sillimanite, zoisite, andalusite, spinel, topaz and opaques. The assemblage, in general, is dominated by hornblende-hypersthene-garnet assemblage, followed by kyanite-sillimanite-andalusite and zircontourmaline-rutile. The high concentration of specific minerals of metamorphic origin reveals high-grade metamorphic terrain as the primary source. The ZTR ratio is low showing low mineralogical maturity. An attempt has also been made to compare the trends of heavy minerals of various sub glacial regions with those of the average values of entire area.  相似文献