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951.
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. 相似文献
952.
A. Joshi 《Natural Hazards》2007,43(1):1-22
The central gap region of Himalaya, which lies in the northern part of the Indian subcontinent, is exposed to great seismic
hazard. A three-dimensional attenuation structure (Q) of this region is obtained using the intensity data of four earthquakes (M 4.3–7.0) in the central Himalayan gap region and the damped least square inversion scheme. The technique is based on that
given by Hashida and Shimazaki (J Phys Earth 32:299–316, 1984). The obtained Q structure explains the spatial distribution of isoseismals of the stronger earthquakes, which occurred in the recent past.
The study area covers the Tehri town, which is the locale of one of the biggest earth fill dams of height 260 m. The spatial
distribution of Q suggests that the Tehri town area is surrounded by lower Q medium, and hence any large earthquake in Tehri will pose great seismic hazard. 相似文献
953.
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. 相似文献
954.
First Order Seismic Microzonation of Delhi,India Using Geographic Information System (GIS) 总被引:2,自引:4,他引:2
William K. Mohanty M. Yanger Walling Sankar Kumar Nath Indrajit Pal 《Natural Hazards》2007,40(2):245-260
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 Mw 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. 相似文献
955.
Manish Kumar Kalpana Kumari AL. Ramanathan Rajinder Saxena 《Environmental Geology》2007,53(3):553-574
Punjab is the most cultivated state in India with the highest consumption of fertilizers. Patiala and Muktsar districts are
two agricultural dominated districts of Punjab located in extreme south-east and south-west of the state. This paper highlights
temporal variations of the groundwater quality and compares its suitability for irrigation and drinking purpose in these two
districts. Water samples were collected in March and September 2003, representing the pre-monsoon and post-monsoon seasons,
respectively. Water samples were analysed for almost all major cations, anions, dissolved heavy metals and turbidity. Parameters
like sodium adsorption ratio, % sodium, residual sodium carbonate, total hardness, potential salinity, Kelley’s ratio, magnesium
ratio, index of base exchange and permeability index were calculated on the basis of chemical data. A questionnaire was also
used to investigate perception of villagers on taste and odour. Comparison of the concentration of the chemical constituents
with WHO (world health organization) drinking water standards of 2004 and various classifications show that present status
of groundwater in Patiala is better for irrigation and drinking purposes except for a few locations with a caution that it
may deteriorate in near future. In Muktsar, groundwater is not suitable for drinking. Higher total hardness (TH) and total
dissolved solids at numerous places indicate the unsuitability of groundwater for drinking and irrigation. Results obtained
in this forms baseline data for the utility of groundwater. In terms of monsoon impact, Patiala groundwater shows dilution
and flushing but Muktsar samples show excessive leaching of different chemical components into the groundwater leading to
the enrichment of different anions and cations indicating pollution from extraneous sources. No clear correlation between
the quality parameters studied here and perceived quality in terms of satisfactory taste response were obtained at electrical
conductivity values higher than the threshold minimum acceptable value. 相似文献
956.
Puthusserry J. Thomas Dontireddy V. Reddy Devender Kumar Pasupuleti Nagabhushanam Balbir S. Sukhija Radhendra N. Sahoo 《Quaternary Geochronology》2007,2(1-4):278-283
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. 相似文献
957.
New statistical models for long-range forecasting of southwest monsoon rainfall over India 总被引:2,自引:0,他引:2
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. 相似文献
958.
Summary The evolution of geophysical parameters over Indian Ocean during two contrasting monsoon years 2002 (drought) and 2003 (normal)
were studied using TRMM/TMI satellite data. Analysis indicates that there was a lack of total water vapour (TWV) build up
over Western Indian Ocean (WIO) during May 2002 (drought) when compared to 2003 (normal). Negative (positive) TWV anomalies
were found over the WIO in May 2002 (2003). In 2002, negative SST anomaly of ∼1.5 °C is found over entire WIO when compared
to 2003. Anomalously high sea surface wind speed (SWS) anomaly over the South West Indian Ocean (SWIO) and WIO would have
resulted in cooling of the sea surface in May 2002 in comparison to 2003. In 2003 the wind speed anomaly over entire WIO and
Arabian Sea (AS) was negative, whereas sea surface temperature (SST) anomaly was positive over the same region, which would
have resulted in higher moisture availability over these regions. A negative (positive) TWV anomaly over Eastern Arabian Sea
(EAS) and positive (negative) anomaly over WIO forms a dipole structure. In the month of June no major difference is seen
in all these parameters over the Indian Ocean. In July 2002 the entire WIO and AS was drier by 10–15 mm as compared to 2003.
The pentad (5 day) average TWV values shows high (>55 mm) TWV convergence over EAS and Bay of Bengal (BoB) during active periods
of 2003, which gives high rainfall over these regions. However, during 2002 although TWV over BoB was >55 mm but it was ∼45–55 mm
over EAS during entire July and hence less rainfall.
The evaporation has been calculated from the bulk aerodynamic formula using TRMM/TMI geophysical products. It has been seen
that the major portion of evaporative moisture flux is coming from southern Indian Ocean (SIO) between 15 and 25° S. Evaporation
in June was more over AS and SIO in 2003 when compared to 2002 which may lead to reduce moisture supply in July 2002 and hence
less rainfall compared to July 2003. 相似文献
959.
Liton Kumar SARKER M. Monowar HOSSAIN M. Anisul HAQUE 《国际泥沙研究》2007,22(3):169-179
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. 相似文献
960.
D.G. Kaskaoutis H.D. Kambezidis Shailesh Kumar Kharol K.V.S. Badarinath 《Atmospheric Research》2007,86(3-4):286-296
This study focuses on the determination of optical depths caused by ozone and trace gases absorption in the Chappuis band, 500–700 nm, and the contribution to the Total Minus Rayleigh Optical Depth (TMROD). The optical depths were derived using the transmission functions implemented in the SMARTS parametric model, while the Total Optical Depths (TODs) were derived by solar extinction measurements obtained in Athens during May 1995. From the data analysis it is obvious that both the ozone and trace gases contribute significantly to TMROD in the Chappuis band. More specifically, the trace gases contributions are higher for air with high pollution levels, while ozone's contribution can be significant under clear-sky conditions. Therefore, the correction in TMROD due to ozone and trace gases optical depths is necessary for an accurate determination of the Aerosol Optical Depth (AOD) in the Chappuis band. The optical depth of ozone is generally removed during the process of the AOD retrievals, since the significance of its absorption in the Chappuis band is well understood. Nevertheless, the optical depth of the trace gases (mainly NO2) is not always taken into account in the AOD retrievals, though its contribution can be significant in urban polluted atmospheres. In this respect, the present study attempts to quantify the ozone and trace gases contributions in an urban environment and to provide some new functions that help estimate the contribution of ozone to the TMROD in the Chappuis band. 相似文献