Escalation of salinity levels in the quaternary aquifers of the Ganga alluvial plain,India

A detailed water quality analysis was carried out in the quaternary aquifer system of the marginal alluvial plain (Ganga Plain) in Bah Tahsil, Agra district, India. The electrical conductivity of 50 samples each from dug wells, hand pumps and tube wells was analysed for the study of salinity levels in shallow, intermediate and deep aquifers. Out of 50, 20 samples of each were also analysed for other chemical constituents such as Na⁺, K⁺, Cl⁻, F⁻ and TDS. The analyses show drastic changes in the salinity levels of shallow, intermediate and deep aquifers. The deep aquifers are more saline compared to the shallow and intermediate aquifers. On the contrary, the concentration of chemical constituents such as Na⁺, K⁺, Cl⁻ and F⁻ was more in the shallow aquifers compared to the deep aquifers. Moreover, there is an indication that the salinity and concentration of the above chemical constituents also escalate with time in each aquifer. The chemical constituents such as Na⁺, K⁺, Cl⁻, F⁻ and TDS range from 51 to 165 mg/l, 1 to 14 mg/l, 224 to 1,459 mg/l, 0 to 1.5 mg/l and 750 to 2,650 mg/l, respectively. Over a 3-year period, the salinity levels have sharply increased and the average F level has increased by 0.1–0.3 mg/l. An attempt has been made here to discuss the factors causing the variation and escalation of chemical constituents and salinity in the water of the three aquifers.     

Attenuation studies based on local earthquake Coda waves in the southern Indian peninsular shield

The Dharwar craton, Cuddapah basin and the Godavari graben characterise three diverse geological and tectonic settings in the peninsular shield of India. Owing to their contiguous proximity, they offer a unique opportunity to document differences, if any, in their seismic wave attenuation characteristics that might have a bearing on the seismogenic nature of the crust in a craton, basin and a rift-like graben structure. An attempt is made here to bring out these differences using constraints from coda-Q. We considered local earthquakes with epicentral distances ranging from␣14 to 150 km recorded at the digital broadband stations at Dharwar (DHD), Cuddapah (CUD) and Kothagudem (KGD) regions to derive the frequency-dependent coda-Q relations. Using the single scattering method, we obtained the frequency-dependent Q _C relationship (Q _C = Q ₀ f ⁿ )for each of the three geological units separately: DHD: Q _C = (730.62 ± 0.09)f ^{(0.54 ± 0.01)}; CUD: Q _C = (535.06 ± 0.13)f ^{(0.59 ± 0.01)} and KGD: Q _C = (150.56 ± 0.08)f ^{(0.91 ± 0.01)}. The Q _C values obtained for all the three sub-regions show moderate to strong frequency dependence and essentially reflect the level of crustal heterogeneities to varying degrees.     

First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS)

A first order seismic microzonation map of Delhi is prepared using five thematic layers viz., Peak Ground Acceleration (PGA) contour, different soil types at 6 m depth, geology, groundwater fluctuation and bedrock depth, integrated on GIS platform. The integration is performed following a pair-wise comparison of Analytical Hierarchy Process (AHP), wherein each thematic map is assigned weight in the 5-1 scale: depending on its contribution towards the seismic hazard. Following the AHP, the weightage assigned to each theme are: PGA (0.333), soil (0.266), geology (0.20), groundwater (0.133) and bedrock depth (0.066). The thematic vector layers are overlaid and integrated using GIS. On the microzonation theme, the Delhi region has been classified into four broad zones of vulnerability to the seismic hazard. They are very high (> 52%), high (38–52%), moderate (23–38%) and less ( < 23%) zones of seismic hazard. The “very high” seismic hazard zone is observed where the maximum PGA varies from 140 to 210 gal for a finite source model of M_w 8.5 in the central seismic gap. A site amplification study from local and regional earthquakes for Delhi region using Delhi Telemetry Network data shows a steeper site response gradient in the eastern side of the Yamuna fluvial deposits at 1.5 Hz. The ‘high’ seismic hazard zone occupies most of the study area where the PGA value ranges from 90 to 140 gal. The ‘moderate’ seismic hazard zone occurs on either side of the Delhi ridge with PGA value varying from 60 to 90 gal. The ‘less’ seismic hazard zone occurs in small patches distributed along the study area with the PGA value less than 60 gal. Site response studies, PGA distribution and destruction pattern of the Chamoli earthquake greatly corroborate the seismic hazard zones estimated through microzonation on GIS platform and also establishes the methodology incorporated in this study.     

Optical dating of liquefaction features to constrain prehistoric earthquakes in Upper Assam, NE India—some preliminary results

Optical dating of liquefied sand structures formed during major earthquakes in Upper Assam, northeast of India, has been carried out to constrain the timing of prehistoric earthquakes in this seismically active region. The bleaching of source material and of the same material during the creation of a liquefaction feature was tested using quartz extracted from 21 samples associated with two different liquefaction structures in Upper Assam. Due to the poor sensitivity of quartz from this region, a sensitisation procedure was used in our SAR protocol to reduce the scatter in optical ages. Various internal consistency tests of the measurement protocol and the excellent reproducibility of the OSL ages indicate that the dose estimates from the quartz are accurate and the optical ages reliable. The preliminary OSL ages indicate that the liquefaction features were formed between 1430 AD and 1630 AD. This study demonstrates that using OSL, ‘direct dating’ of prehistoric earthquakes may be possible, if sand blows from liquefied dykes are preserved.     

New statistical models for long-range forecasting of southwest monsoon rainfall over India

The India Meteorological Department (IMD) has been issuing long-range forecasts (LRF) based on statistical methods for the southwest monsoon rainfall over India (ISMR) for more than 100 years. Many statistical and dynamical models including the operational models of IMD failed to predict the recent deficient monsoon years of 2002 and 2004. In this paper, we report the improved results of new experimental statistical models developed for LRF of southwest monsoon seasonal (June–September) rainfall. These models were developed to facilitate the IMD’s present two-stage operational forecast strategy. Models based on the ensemble multiple linear regression (EMR) and projection pursuit regression (PPR) techniques were developed to forecast the ISMR. These models used new methods of predictor selection and model development. After carrying out a detailed analysis of various global climate data sets; two predictor sets, each consisting of six predictors were selected. Our model performance was evaluated for the period from 1981 to 2004 by sliding the model training period with a window length of 23 years. The new models showed better performance in their hindcast, compared to the model based on climatology. The Heidke scores for the three category forecasts during the verification period by the first stage models based on EMR and PPR methods were 0.5 and 0.44, respectively, and those of June models were 0.63 and 0.38, respectively. Root mean square error of these models during the verification period (1981–2004) varied between 4.56 and 6.75% from long period average (LPA) as against 10.0% from the LPA of the model based on climatology alone. These models were able to provide correct forecasts of the recent two deficient monsoon rainfall events (2002 and 2004). The experimental forecasts for the 2005 southwest monsoon season based on these models were also found to be accurate.     

SHEAR STRESS FOR INITIATION OF MOTION OF NON-UNIFORM SEDIMENT MIXTURES

Experiments on initiation of motion of different fractions of non-uniform sediment mixtures are reported. Four sediment mixes and reference transport method to define the threshold of bed particle movement are used in this analysis. Factors controlling the initiation of motion are analyzed. It is found that relative size of different grains with respect to a median size greatly affects the initiation of movement. The incipient motion of non-uniform sediment is very much dependent on the absolute size for coarser fractions. Considering the factors controlling the initiation of motion the experimental data sets along with the other available data yield a new relationship for the calculation of critical shear stress of non-uniform sediments. A set of equations have found that all the data points fall into a single line for the finer and for coarser fractions.     

Fluorescence efficiencies of electrons in second positive bands of N2 and first negative bands of N2+

Fluorescence efficiencies of electrons in a large number of bands of N₂ second positive and N_2⁺ first negative groups lying in the 3000–5200 Å region are calculated. At very low pressure where quenching is negligible the present values are within 15 per cent of the experimental data of Hartmann (1968). The efficiencies are found to be independent of the impact energies greater than 200 eV which is in accordance with other theoretical and experimental results. The ratio of the total efficiencies in N₂ second positive and N_2⁺ first negative groups is 1·31 and is about 20 per cent lower than the experimental values. The efficiencies at a higher pressure equal to 600 torr are compared with the experimental data of Davidson and O'Neil (1964a).     

Mercury's atmosphere: A perspective after Mariner 10

Measurements made during the Mariner 10 flybys of Mercury have shown that this planet has a tenuous atmosphere, somewhat similar to that of the Moon, which consists of at least helium and can be classified as an exosphere. The amount of helium observed can be supplied by either the accretion of only a fraction of the solar wind He²⁺ diffusing across the magnetopause, or from outgassing of radiogenic helium from the planetary crust. The role of solar wind in the maintenance and depletion of Mercury's atmosphere is discussed in view of the density upper limits established from Mariner 10. The argon supply rate on Mercury is probably not more than that on the Earth, but it is difficult to say whether Mercury is deficient in potassium or not on the basis of the present data. The global outgassing of CO₂ and H₂O from the planet interior is estimated to be at least four orders of magnitude smaller than for Earth which indicates that either Mercury is deficient in volatiles or that this planet is very inactive.     

A paleolimnological record of Holocene climate and environmental change in the Temagami region,northeastern Ontario

The Arcellacean (Thecamoebian) fauna was assessed in five Holocene sediment cores obtained from James and Granite lakes in the Temagami region of northeastern Ontario. In addition, palynological analysis was carried out on two of these cores, one each from James and Granite lakes. The first indication of postglacial colonization by plants was the appearance of rare Cupressaceae pollen, dated to 10,800 yr BP. Plant diversity began to increase by 10,770 yr BP when Pinus spp. and Larix migrated into the area. The first appearance of arcellaceans occurred after 9650 yr BP in assemblages dominated by Centropyxis constricta and opportunistic Centropyxis aculeata. High abundances of charophytes in the cores until 8800 yr BP indicated that macroalgae were proliferating at this time. This deposition is interpreted to have occurred during the draining of an ice-marginal lake following the retreat of the Laurentide Ice Sheet. Based on pollen analysis, warmer conditions associated with the Holocene Hypsithermal prevailed in the area from 6250 to 4115 yr BP. The stable, open Great Lakes – St. Lawrence type forest that developed here at the beginning of the Hypsithermal continues to prevail to the present. The periodic colonization of the lake by beavers (Castor canadensis) acted as a control on water-level and eutrophication through the Holocene. Evidence of eutrophication was indicated in the core samples by the abundance of high levels of the alga Pediastrum and the arcellacean Cucurbitella tricuspis. Eutrophication periodically developed when beavers dammed a site, causing the rate of flow in drainage streams to slow and stagnant conditions occurred. When the site became depleted of the nearby trees, which were preferred by beaver (Betula, Alnus and Populus), the dam would be abandoned, causing the water-level to drop. Stagnant conditions were reduced as flow levels increased, reducing eutrophication and resulting in recovering forest stands. In addition, the lowering water levels would result in encroachment of the forest along the lake shore. This cycle occurred many times in the history of this lake as indicated by fluctuations in the size of arcellacean populations.     

Development of micro-scale joints in volcanic rocks under thermal stress

Petrographic studies of samples of the Rajmahal basalt reveal a variety of microscopic joints within phenocrysts, which seem to have developed under the influence of thermal stresses during cooling. The theoretical analysis shows that: