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81.
The present study presents a review on the progressive development of the seismic zonation map of India both from official agencies and also from independent individual studies. The zonation map have been modified and updated regularly with the occurrence of major destructive earthquakes over the years in the Indian subcontinent with the addition of new data. This study discusses the criteria chosen for the progressive zonation and the major earthquakes that were responsible for retrospection of the earlier published maps. The seismic zonation maps of India have also been prepared by various independent workers by adopting different approaches to achieve the purpose of the zonation. Despite the endeavors from various sources to provide a solution for the problem of earthquake hazards in India, there were many limitations on the zonation map as it gives the picture at a regional scale mostly on the bedrock level without addressing the local site conditions. But nevertheless, the seismic zonation map gives basic guidelines for any region to know the hazard scenario and if any city or urban population is under threat from seismic point of view, further site specific seismic microzonation may be carried out. In the International scenario, the Global Seismic Hazard Assessment Program (GSHAP) in 1999 prepared a hazard map for world in terms of peak ground acceleration (PGA) with a 10% probability of exceedance in 50 years, but it turned out to be an underestimation of the hazard parameter when compared with the observed PGA. To tackle the problem of seismic hazards, there was a need to have a detail study on the local site conditions in terms of its geological, geophysical and geotechnical properties. With the advent of better instrumentation and knowledge on the mechanics of earthquakes, it was possible to identify zones of hazards at a local level and this gives rise to the study of seismic microzonation. Seismic microzonation work has been carried out in India in some of the strategic important mega cities and industrial build up that has the potential of being damaged from future earthquakes, as has been shown in the past. Though the microzonation map is not the final output map, as it can still be updated at later stage with more input data, it does provide a more realistic picture on the site specific seismic hazard. 相似文献
82.
The evolution of east coast of India sis discussed within the ambit of clearly identifiable four major tectonic stages which
had a profound effect in shaping the tectonic grain of the east coast basins. The evolutionary process began with rift related
crustal extension between India and Sri Lanka as a consequence of Africa-Antarctica rifting and development of Natal Basin.
An arm of this rift led to initial extension in the Cauvery Basin and failed. Later, the India-West Australia rift propagated
further in southwesterly direction initiating Mahanadi and Krishna-Godavari Basins. This extension was an oblique one with
Nayudupeta high acting as pivot. The oblique extension followed by asymmetric seafloor spreading developed transpression along
India-Sri Lanka and Antarctica junction, resulting in a NNW-SSE trending transcurrent fault along which Antarctica moved southward.
Subsequently, entire east coast evolved through a more or less uniform post rift stage. 相似文献
83.
In the present paper the intensity of serration of quartz grain boundary sutures in the Palaeoproterozoic age Malanjkhand
granite (Central India) is quantified using the ruler method of fractal analyses. The northern margin of the granite has proximity
to the Central Indian Suture (CIS) that forms the southernmost part of Central Indian Tectonic Zone (CITZ) along which amalgamation
of the northern and southern Indian shields took place. The fractal dimension (D) of the quartz sutures is calculated in 13
samples collected at varying distance from the CIS. D values are noted to increase in samples towards the CIS. This demonstrates
the influence of the tectonic events along the CIS on fabric development in the Malanjkhand granite. Magmatic fabric defined
by preferentially oriented feldspar laths and high-T solid-state deformation fabrics are observed in areas distant from the
CIS. In contrast, mylonites and low-T fabrics such as bulging quartz grain boundaries occur in proximity to the CIS. It is
inferred that the emplacement and high-T fabric development in the Malanjkhand granite was synchronous with regional accretionary
processes that occurred in the region during the Palaeoproterozoic. Two different possibilities, one involving a single tectonic
event and the other involving multiple tectonic events are discussed to explain the superimposition of low-T over high-T fabric
due to which intensity of quartz grain boundary serration increases towards the CIS. 相似文献
84.
Study of subsurface geology in locating arsenic-free groundwater in Bengal delta,West Bengal,India 总被引:1,自引:0,他引:1
Over a large area of the Bengal delta in West Bengal, India, arsenic distribution patterns in groundwater were studied. One
hundred and ten boreholes at different target locations were made, subsurface sediments were logged and analysed, and arsenic
values in sediments vis-à-vis groundwater were compared. The study elucidates the subsurface geology of the western part of
Bengal delta and characterises the sediments that were intersected in different boreholes with contrasting values of arsenic
in groundwater. It reveals an existence of multiple aquifers stacked over each other. Depending on the color and nature of
aquifer-sands and their overlying clay beds six aquifer types (Type-1 to Type-6) are classified and described. Sediment-arsenic
for all the varieties of aquifer sands are near similar but the groundwater-arsenic of these six aquifers varies widely. Type-2
and Type-5 aquifers host arsenic-contaminated groundwater whereas the other four aquifers are arsenic-free. Type-2 and Type-5
aquifers are capped by a grey to dark grey soft organic matter-rich clay unit which makes these aquifers semi-confined to
leaky-confined. These contribute in releasing arsenic from the sediments. The results of this study are employed in a proposed
georemedial measure against this hazardous toxic element. 相似文献
85.
The 560-km-long Kerala coast is characterised by long barriers with narrow beaches and steep cliffs. Distribution of cliffs
from nine sections measuring a cumulative length of 63.5 km is evaluated in ArcGIS Software using topomaps and field survey
data. The cliff sections in the southern coast comprise both permeable and impermeable rocks, whereas those along northern
coast are comprised of either Precambrian crystalline and/or Tertiary formations. Notches, caves and even small arches are
developed in Cannanore, Dharmadam and Kadalundi cliffs, where only primary laterites are exposed to wave attack. Stacks composed
of laterite and Precambrian crystallines found in nearshore of cliffed coast indicate recession of shoreline. Mass wasting,
mudslide and mudflow type of cliff failures are common in permeable to semi-permeable rocks, whereas rotational sliding, rockfall
and toppling failure are found in hard rock cliffs. Retreat of cliff sections are induced by natural or anthropogenic activities
or both. Rate of recession vary from a few centimetres to one metre/year depending upon the nature of lithology, structures
and recession agents acting upon the cliffs. Various methods of cliff protection for e.g. hard structures—revetments, groins,
seawalls, breakwater and jetties—and soft measures—artificial reefs/marsh creation, floating breakwaters, beach nourishment,
beach scraping and vegetation planting—are suggested. 相似文献
86.
Arsenic is present in groundwater at Siliguri–Jalpaiguri area, West Bengal, India. This is the place where Tista river descending
from the Himalayas meets the alluvial plain. The area represents alluvial fan and floodplains of Tista, Mahananda-Balasan,
Jaladhaka and its tributaries. In the river sediment samples, para- and ferro-magnetic minerals within 0.3–0.05 mm fraction
contain 9–80 ppm of arsenic. The study indicates that iron bearing minerals viz. biotite, hornblende as well as iron coated
grains of the sediment are major contributors towards arsenic budget. Though magnetite as a mineral shows maximum arsenic
content (22 ppm), it is volumetrically not of much significance. Measurement of groundwater collected from tube wells shows
up to 0.05 ppm of arsenic. These arsenic contaminated tube wells occur in a linear fashion along the course of the rivers.
Moreover, localization of contaminated tube wells coincides with the change of channel gradient as observed in longitudinal
section. The study enumerates a cause–effect relationship of arsenic occurrence with river gradient and fluvial sedimentation. 相似文献
87.
The impacts of global warming on farmers in Brazil and India 总被引:1,自引:0,他引:1
How big a threat is global warming to climate-sensitive and economically important sectors such as agriculture in developing countries? How well will farmers be able to adapt to the threats of global warming? This paper attempts to shed light on these two important questions. A cross-sectional analysis is employed to estimate the climate sensitivity of agriculture in Brazil and India. Using panel data from both countries, the study measures how net farm income or property values vary with climate, and consequently, how farmers in India and Brazil react and adapt to climate. The estimated relationships are then used to predict the consequence of alternative climate scenarios. Global warming by the end of the next century could cause annual damages in Brazil between 1% and 39% and between 4% and 26% in India, although some of this effect may be potentially offset by carbon fertilization. These estimates do not factor into account climate-induced extreme weather events. 相似文献
88.
In this paper, flood problems in India, regional variabilityof the problem, present status of the ongoing management measures, their effectiveness and futureneeds in flood management are covered. Flood problems in India are presented by four zonesof flooding, viz. (a) Brahmaputra River Basin, (b) Ganga River Basin, (c) North-WestRivers Basin, and (d) Central India and Deccan Rivers Basin. Some special problems,related to floods like dam break flow, and water logging in Tal areas, are also mentioned.Progress of various flood management measures, both structural and non-structural, arediscussed. In addition, future needs to achieve efficient and successful flood managementmeasures in India are also pointed out. 相似文献
89.
Characterisation of the Dabla Granitoids, North Khetri Copper Belt, Rajasthan, India: Evidence of Bimodal Anorogenic Felsic Magmatism 总被引:1,自引:0,他引:1
Naveen Chaudhri Parampreet Kaur Martin Okrusch Annette Schimrosczyk 《Gondwana Research》2003,6(4):879-895
The Palaeoproterozoic Dabla granitoid pluton of the North Khetri Copper Belt is located to the east of a NNE-SSW trending lineament with numerous albite-rich intrusives, the intraplate ‘albitite line’. The Dabla pluton is essentially made up of calcic amphibole-bearing granitoids, displaying a concentric bimodal distribution of alkali-feldspar granites, comprising a microcline-albite granite and an albite-granite. The dominant rock type is pink-coloured granite, which is characterised by quartz, microcline, albite and hastingsitic hornblende, and occurs in the marginal parts of the pluton. The volumetrically subordinate albite-granite in the central part of the pluton is invariably white in colour, non-foliated and is mainly composed of quartz, albite and amphibole of actinolite to ferro-actinolite composition. The albite-granite is characterised by low K2O (0.06-0.09%), Rb (<5 ppm) and Ba (<20 ppm), high Na2O (7.19-7.36%) and high Na/K ratios (122.4-185.2) as compared to the granite. These rocks are not subjected to any metamorphic overprint, especially the albite-granite, which shows pristine abundances of major and trace elements. The rocks are highly evolved as reflected in their high SiO2 (72 to 78%) contents and high DI (89.5-97) values. The Dabla granitoids are characterised by similar REE and spider patterns, displaying LREE enriched slopes, flat HREE profiles and strong negative Sr, P, Ti and Eu anomalies suggesting their comagmatic nature. Nevertheless, the granite is relatively more fractionated [(La/Yb)N = 3.89-8.19] and show higher REE abundances (466-673 ppm) as compared to the albite-granite [(La/Yb)N = 1.97-2.96; REE = 220-277 ppm]. Distinctive features of these rocks are their low Ca (0.21-1.53%), Mg (<0.02-0.19%), Al (11.84-12.96%) and Sr (12-46 ppm) abundances, high Zr (155-631 ppm), Y (67-156 ppm), Nb (14-91 ppm), and Ga (20-31 ppm) concentrations and high Fe*-number, high Ga/Al ratio and high agpaitic index (AI) values. These features, coupled with their ferroan, alkaline and metaluminous nature, are typical of within-plate aluminous A-type granites. The geochemical data further indicate that the Dabla magma was generated at fairly high temperature, apparently in an upper mantle region, under relatively low H2O activities and reduced conditions and emplaced at a shallow depth in an extensional tectonic environment. 相似文献
90.
Flexure of the Indian plate and intraplate earthquakes 总被引:2,自引:0,他引:2
The flexural bulge in central India resulting from India's collision with Tibet has a wavelength of approximately 670 km.
It is manifest topographically and in the free-air gravity anomaly and the geoid. Calculations of the stress distribution
within a flexed Indian plate reveal spatial variations throughout the depth of the plate and also a function of distance from
the Himalaya. The wavelength (and therefore local gradient) of stress variation is a function of the effective elastic thickness
of the plate, estimates of which have been proposed to lie in the range 40–120 km. The imposition of this stress field on
the northward moving Indian plate appears fundamental to explaining the current distribution of intraplate earthquakes and
their mechanisms. The current study highlights an outer trough south of the flexural bulge in central India where surface
stresses are double the contiguous compressional stresses to the north and south. The Bhuj, Latur and Koyna earthquakes and
numerous other recent reverse faulting events occurred in this compressional setting. The N/S spatial gradient of stress exceeds
2 bars/km near the flexural bulge. The overall flexural stress distribution provides a physical basis for earthquake hazard
mapping and suggests that areas of central India where no historic earthquakes are recorded may yet be the locus of future
damaging events. 相似文献