Evaluating the seismic hazard to the National Capital (Delhi) Region,India, from moderate earthquakes using simulated accelerograms     

Dinesh Kumar  Irene Sarkar  V. Sriram  S. S. Teotia 《Natural Hazards》2012,61(2):481-500

The National Capital Region (NCR) of India is exposed to high seismic hazard and risk due to a great earthquake in the central seismic gap of Himalaya and/or due to moderate-size earthquake within NCR. The high population density, rapid growth of infrastructure, and old engineering structures in the region make it more vulnerable to the human as well as economic loss due to moderate-size earthquakes also. The evaluation of seismic hazard is the first step to prepare a proper mitigation plan for the region. The aim of this paper is to evaluate the seismic hazard and risk due to moderate-size earthquakes in the vicinity of NCR. For this purpose, a suit of accelerograms have been generated from hypothetical moderate-size earthquakes (M 5.5 and 6.0) in the region. A basic fault-plane solution is assumed for this purpose. The ranges of the different parameters like depth of focus and stress drop values have been used in order to examine the effect of these parameters on hazard. The accelerograms have been synthesized using two basic velocity models, one representing a hard site and the other a site with a significant low-velocity cover. These two velocity models represent the ridge area and trans-Yamuna river area in the NCR. The decay of peak ground acceleration (pga) values with distance is fast in trans-Yamuna region (with low-velocity surface layer of 100 m) as compared to that of ridge area (with low-velocity surface layer of 1 m). Also, the decay of pga becomes slower if we increase the depth of focus from 10 to 20 km. The response spectra (5% damping) of the synthetic accelerograms for the three periods T = 0.4s, 0.75s, and 1.25s have been estimated and presented in the form of decay curves. The amplifications as a function of epicentral distance and stress drop have also been estimated. We note that the amplifications in 100-m layer case do not occur uniformly at all the distances, rather it is dependent on the angle of incidence of energy into the layers. The pga values are generally amplified by more than twice with increase in stress drop from 100 to 400 bars. The seismic exposure of the population in Delhi city has been presented. The results presented in this study may serve as an important input in the planning of mitigation and disaster management programs in the National Capital Region.  相似文献   

Characterizing air–sea CO2 exchange dynamics during winter in the coastal water off the Hugli-Matla estuarine system in the northern Bay of Bengal, India     

Anirban Akhand  Abhra Chanda  Sachinandan Dutta  Sudip Manna  Sugata Hazra  Debasis Mitra  K. H. Rao  V. K. Dadhwal 《Journal of Oceanography》2013,69(6):687-697

The distribution of the fugacity of CO₂ ( $ f_{{{\text{CO}}_{ 2} }} $ ) and air–sea CO₂ exchange were comprehensively investigated in the outer estuary to offshore shallow water region (lying adjacent to the Sundarban mangrove forest) covering an area of ~2,000 km² in the northern Bay of Bengal during the winter. A total of ten sampling surveys were conducted between 1 December, 2011 and 21 February, 2012. Physico-chemical variables like sea surface temperature (SST), salinity, pH, total alkalinity (TAlk), dissolved inorganic carbon (DIC) and in vivo chlorophyll-a along with atmospheric variables were measured in order to study their role in controlling the CO₂ flux. Surface water $ f_{{{\text{CO}}_{ 2} }} $ ranged between 111 and 459 μatm which correlated significantly with the SST (r = 0.71, p < 0.001, n = 62). Neither DIC nor TAlk showed any linear relationship with varying salinity in the estuarine mixing zone, demonstrating the significant presence of non-carbonate alkalinity. An overall net biological control on the surface $ f_{{{\text{CO}}_{ 2} }} $ distribution was established during the study, although no significant correlation was found between chlorophyll-a and $ f_{{{\text{CO}}_{ 2} }} $ (water). The shallow water region studied was mostly under-saturated with CO₂ and acted as a sink for atmospheric CO₂. The difference between surface water and atmospheric $ f_{{{\text{CO}}_{ 2} }} $ ( $ \Updelta f_{{{\text{CO}}_{ 2} }} $ ) ranged from ?274 to 69 μatm, with an average seaward flux of ?10.5 ± 12.6 μmol m^?2 h^?1. The $ \Updelta f_{{{\text{CO}}_{ 2} }} $ and hence the air–sea CO₂ exchange was primarily regulated by the variation in sea surface $ f_{{{\text{CO}}_{ 2} }} $ , since atmospheric $ f_{{{\text{CO}}_{ 2} }} $ varied over a comparatively narrow range of 361.23–399.05 μatm.  相似文献   

Provenance and weathering history of Mesoproterozoic clastic sedimentary rocks from the basal Gulcheru Formation,Cuddapah Basin     

Gopal Chakrabarti  Debashish Shome  Blanca Bauluz  Subhajit Sinha 《Journal of the Geological Society of India》2009,74(1):119-130

Geochemical analysis for the Mesoproterozoic clastic sedimentary rocks of the basal Gulcheru Formation of the Cuddapah Basin in the Gugudu-Dadithota-Parnapalle-Palkonda region (extending atleast 40 km) have been performed to highlight their provenance and weathering history. The low K₂O/Al₂O₃ ratios of the representative samples points to the recycled nature of sediments and illite clay in the sediments indicate an overall cold climate (low chemical weathering degree). All the provenance diagrams indicate a mixed source of the Gulcheru sediments with felsic dominancy and Upper continental crust (UCC) signature.  相似文献   

Geochemistry and provenance of stream sediments of the Ganga River and its major tributaries in the Himalayan region,India     

Pramod Singh 《Chemical Geology》2010,269(3-4):220-236

Major, trace and REE compositions of sediments from the upper Ganga River and its tributaries in the Himalaya have been examined to study the weathering in the Himalayan catchment region and to determine the dominant source rocks to the sediments in the Plains. The Ganga River rises in the Higher Himalaya from the Higher Himalayan Crystalline Series (HHCS) bedrocks and traverses over the Lesser Himalayan Series (LHS) and the Himalayan foreland basin (Siwaliks) rocks before entering into the Gangetic Plains. The major element compositions of sediments, reflected in their low CIA values (45.0–54.7), indicate that silicate weathering has not been an important process in the Himalayan catchment region of the Ganga River. Along the entire traverse, from the HHCS through LHS and the Siwaliks, the sediments from the tributaries and the mainstream Ganga River show higher Na₂O, K₂O, CaO and silica. This, and the higher ratios of La/Sc, Th/Sc and lower ratios of Co/Th, suggest that the source rocks are felsic. The fractionated REE patterns and the significant negative Eu anomalies (Eu/Eu? = 0.27–0.53) indicate highly differentiated source. Moreover, the comparison of the sediments with different source rock lithologies from the HHCS and the LHS for their major elements clearly suggests that the HHCS rocks were the dominant source. Further, comparison of their UCC (upper continental crust) normalized REE patterns suggests that, among the various HHCS rocks, the metasediments (para-gneiss and schist) and Cambro-Ordovician granites have formed the major source rocks. The Bhagirathi and Alaknanda River sediments are dominantly derived from metasediments and those in the Mandakini River from Cambro-Ordovician granites. The resulting composition of the sediments of the Ganga River is due to the mixing of sediments supplied by these tributaries after their confluence at Devprayag. No further change in major, trace and rare earth element compositions of the sediments of the Ganga River after Devprayag up to its exit point to the Plains at Haridwar, suggests little contribution of the Lesser Himalayan and Siwalik rocks to the Ganga River sediments.  相似文献   

Signatures of rift environment in the production of garnet-amphibolites and eclogites from Tso-Morari region, Ladakh, India: A geochemical study     

D. Rameshwar Rao  Hakim Rai 《Gondwana Research》2006,9(4):512-523

The geochemistry of eclogites and garnet-amphibolites from Tso-Morari region, Ladakh, India has been investigated to characterize their protoliths on the basis of immobile elements, especially trace elements including REE. The eclogites and garnet-amphibolites have coherent compositions, except for the UHP metamorphic minerals being preserved in eclogites. Compositionally, the metabasites range from ‘depleted’ to ‘enriched’, and span from within-plate basalts (WPB) to MORB fields, and match with various enriched or ‘transitional’ MORB types (e.g., on Ti–Zr–Y and Nb–Zr–Y ternary plots). Isotopically they have Sr_i ratio 0.706 which is similar to some of the Ocean Island Basalt (OIB). The rocks under study suggest that the enriched components are probably derived by melting of a mantle source with an enriched OIB-type component rather than due to the crustal contamination. We propose a rift environment for their protoliths and relate to advanced intra-continental rift situation. Furthermore, our geochemical studies envisage an initial phase of plume activity (Cambrian or earlier) resulting in basaltic magma in the eclogitic layers at sub-lithospheric levels, wherein they were subjected to crystallization under ultra-high pressure conditions. At a later stage the reactivation of faults (probably during Permo-Triassic times) acted as channels for the emplacement of the high pressure rocks in the continental crust. Subsequently, the ultra-high pressure rocks got re-equilibrated as amphibolites, with some remaining as relict eclogites, which later got exposed to the surface during various phases of the Himalayan uplift.  相似文献   

The effect of pH of water and mineralogical properties on the slake durability (degradability) of different rocks from the Lesser Himalaya, India     

Vikram Gupta  Iqrar Ahmed 《Engineering Geology》2007,95(3-4):79-87

Slake durability is an important geotechnical parameter and is a measure of degradability of rocks due to the process of mechanical and chemical breakdown. It is closely related to the mineralogical composition and the texture of the rocks. In this paper, mineralogical examination along with slake durability tests under variable pH conditions, both in acidic and alkaline environments, on the limestone, shale and siltsone were evaluated to understand the relationship between mineralogy and the degradability of rocks. The study revealed that rocks rich in calcium carbonate and or magnesium carbonate are adversely affected in the acidic environment, whereas, the rocks rich in quartz, feldspar and muscovite are independent of the pH of the slaking fluid, which in turn, is more influenced by the texture of the constituent minerals. It has also been observed that fine grained rocks are more susceptible to degrade in comparison to the coarse grained rocks.  相似文献   

Petrological and Geochemical Characteristics of Archean Gneisses and Granitoids from Bastar Craton, Central India – Implication for Subduction Related Magmatism     

M.F. Hussain  M.E.A. Mondal  T. Ahmad   《Gondwana Research》2004,7(2):531-537

The gneisses and granitoids of Bastar craton (with rock suites up to 3.5 Ga) show calc-alkaline trondhjemitic characteristics. The rocks are enriched in both LILE and HFSE than primordial mantle. They have also relatively higher abundances of LILE and strong depletion at P and Ti in the multielement diagram. The depletion of Ti and P indicates retention of these elements by titanite and/or apatite during partial melting. It is proposed that subduction of an oceanic slab and its consequent melting led to the formation of the protoliths of the gneisses without much interaction with the mantle wedge. The granitoids represent temporally distinct suites formed in response to further melting of slab at greater depth and interaction of magma with the mantle wedge during their transport to the crust.  相似文献   

Forest management using remote sensing and GIS in Barbatpur range, Betul forest division     

I. J. Singh  Sanjay Moharir 《Journal of the Indian Society of Remote Sensing》2003,31(3):149-156

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Origin of the sparry magnesite deposits around Bauri,Almora district,Uttar Pradesh,India     

M. N. Joshi  A. K. Bhattacharya  M. S. Anantharaman 《Mineralium Deposita》1993,28(2):146-152

Seven pockets of variable dimensions of strata-bound sparry magnesite within the Middle Proterozoic Gangolihat Formation around Bauri in the Almora district, Kumaun, Lesser Himalaya, have been investigated petrographically and geochemically. The lenses and pockets of megacrystalline, bladed, occasionally stellate, magnesite aggregates invariably enclosed by stromatolitic or massive dolostones, often exhibit a concordant relationship with the latter. Besides the sharp contrast in crystal-linity of magnesite and dolostones and the patches of the latter in the former, relict features such as layers of chert, cryptocrystalline silica veins and stromatolitic structures are discernible in the magnesite. There is a gradual increase in MgO and FeO with a corresponding decrease in CaO, and a striking depletion in Sr from dolostone to magnesite but no noteworthy variation in other major or minor elements nor in insoluble contents. Both the dolostones and magnesites are characterised by the same range of oxygen isotope ratios. However, a marked enrichment of lighter carbon isotopes in magnesites is noted. Based on these observations, it is inferred that the magnesite around Bauri is a product of diagenetic magnesitisation of penecontemporaneous dolomite in a restricted biohermal tidal flat environment.  相似文献   

Soil erosion assessment and mapping of the algar river watershed (uttar pradesh) using remote sensing technique     

SK Saha  BM Singh 《Journal of the Indian Society of Remote Sensing》1991,19(2):67-76

This study was undertaken to prepare an inventory on soil erosion of a hilly river watershed — the Aglar watershed, part of Tehri Garhwal and Dehradun districts (U.P.), using terrain physiography and soil survey data obtained from interpretation and analysis of Landsat TM FCC (1:62,500 scale) and limited ground investigations. The watershed is divided into four broad physiographic units viz. higher Himalayas (> 2000m elevation); lower Himalayas (< 2000m elevation); river terraces and flood plains. Each physiographic unit has been further divided into subunits on the basis of aspects and landuse. Three major orders of soils viz. Inceptisols, Mollisols and Entisols were found in different physiographic units. Soil, and land properties of soilscape units viz. soil depth, texture, structure, slope, landuse and soil temperature regime were evaluated for soil-erosion hazard. The results indicate that in the whole watershed 19.13%, 45.68%, 26.51% and 7.92% areas have been found to be under none to slight, moderate, severe and very severe soil erosion hazard categories, respectively.  相似文献