Earthquake hazard zonation of Sikkim Himalaya using a GIS platform

An earthquake hazard zonation map of Sikkim Himalaya is prepared using eight thematic layers namely Geology (GE), Soil Site Class (SO), Slope (SL), Landslide (LS), Rock Outcrop (RO), Frequency–Wavenumber (F–K) simulated Peak Ground Acceleration (PGA), Predominant Frequency (PF), and Site Response (SR) at predominant frequencies using Geographic Information System (GIS). This necessitates a large scale seismicity analysis for seismic source zone classification and estimation of maximum earthquake magnitude or maximum credible earthquake to be used as a scenario earthquake for a deterministic or quasi-probabilistic seismic scenario generation. The International Seismological Center (ISC) and Global Centroid Moment Tensor (GCMT) catalogues have been used in the present analysis. Combining b-value, fractal correlation dimension (Dc) of the epicenters and the underlying tectonic framework, four seismic source zones are classified in the northeast Indian region. Maximum Earthquake of M _W 8.3 is estimated for the Eastern Himalayan Zone (EHZ) and is used to generate the seismic scenario of the region. The Geohazard map is obtained through the integration of the geological and geomorphological themes namely GE, SO, SL, LS, and RO following a pair-wise comparison in an Analytical Hierarchy Process (AHP). Detail analysis of SR at all the recording stations by receiver function technique is performed using 80 significant events recorded by the Sikkim Strong Motion Array (SSMA). The ground motion synthesis is performed using F–K integration and the corresponding PGA has been estimated using random vibration theory (RVT). Testing for earthquakes of magnitude greater than M _W 5, a few cases presented here, establishes the efficacy and robustness of the F–K simulation algorithm. The geohazard coverage is overlaid and sequentially integrated with PGA, PF, and SR vector layers, in order to evolve the ultimate earthquake hazard microzonation coverage of the territory. Earthquake Hazard Index (EHI) quantitatively classifies the terrain into six hazard levels, while five classes could be identified following the Bureau of Indian Standards (BIS) PGA nomenclature for the seismic zonation of India. EHI is found to vary between 0.15 to 0.83 quantitatively classifying the terrain into six hazard levels as “Low” corresponding to BIS Zone II, “Moderate” corresponding to BIS Zone III, “Moderately High” belonging to BIS Zone IV, “High” corresponding to BIS Zone V(A), “Very High” and “Severe” with new BIS zones to Zone V(B) and V(C) respectively.     

Recent seismicity in Northeast India and its adjoining region

Recent seismicity in the northeast India and its adjoining region exhibits different earthquake mechanisms – predominantly thrust faulting on the eastern boundary, normal faulting in the upper Himalaya, and strike slip in the remaining areas. A homogenized catalogue in moment magnitude, M _W, covering a period from 1906 to 2006 is derived from International Seismological Center (ISC) catalogue, and Global Centroid Moment Tensor (GCMT) database. Owing to significant and stable earthquake recordings as seen from 1964 onwards, the seismicity in the region is analyzed for the period with spatial distribution of magnitude of completeness m _t, b value, a value, and correlation fractal dimension D _C. The estimated value of m _t is found to vary between 4.0 and 4.8. The a value is seen to vary from 4.47 to 8.59 while b value ranges from 0.61 to 1.36. Thrust zones are seen to exhibit predominantly lower b value distribution while strike-slip and normal faulting regimes are associated with moderate to higher b value distribution. D _C is found to vary from 0.70 to 1.66. Although the correlation between spatial distribution of b value and D _C is seen predominantly negative, positive correlations can also be observed in some parts of this territory. A major observation is the strikingly negative correlation with low b value in the eastern boundary thrust region implying a possible case of extending asperity. Incidentally, application of box counting method on fault segments of the study region indicates comparatively higher fractal dimension, D, suggesting an inclination towards a planar geometrical coverage in the 2D spatial extent. Finally, four broad seismic source zones are demarcated based on the estimated spatial seismicity patterns in collaboration with the underlying active fault networks. The present work appraises the seismicity scenario in fulfillment of a basic groundwork for seismic hazard assessment in this earthquake province of the country.     

Timing and preservation mechanism of deglacial pteropod spike from the Andaman Sea,northeastern Indian Ocean

The aragonite compensation depth (ACD) fluctuated considerably during the last glacial until the Holocene with a dominant pteropod preservation spike during the deglacial period, which is prominently seen in three well‐dated cores covering the Andaman Sea, northeastern Indian Ocean. The precise time period of the preservation spike of pteropods is not known but this knowledge is crucial for stratigraphical correlation and also for understanding the driving mechanism. Isotopic and foraminiferal proxies were used to decipher the possible mechanism for pteropods preservation in the Andaman Sea. The poor preservation/absence of pteropods during the Holocene in the Andaman Sea may have implications for ocean acidification, driven by enhanced atmospheric CO₂ concentration. Strengthening of the summer monsoon and the resultant high biological productivity may also have played a role in the poor preservation of pteropods. The deglacial pteropod spike is characterized by high abundance/preservation of the pteropods between ～19 and 15 cal. ka BP, associated with very low atmospheric CO₂ concentration. Isotope data suggest the prevalence of a glacial environment with reduced sea surface temperature, upwelling and enhanced salinity during the pteropod preservation spike. Total planktic foraminifera and Globigerina bulloides abundances are low during this period, implying a weakened summer monsoon and reduced foraminiferal productivity. Based on the preservation record of pteropods, it is inferred that the ACD was probably deepest (>2900 m) at 16.5 cal. ka BP. The synchronous regional occurrence of the pteropod preservation spike in the Andaman Sea and in the northwestern Indian Ocean could potentially be employed as a stratigraphic marker.     

Bioavailability of arsenic in the soil horizon: a laboratory column study

Groundwater contaminated with arsenic (As), when extensively used for irrigation, causes potentially long-term detrimental effects to surface soils. Such contamination can also directly affect human health when irrigated crops, such as rice, vegetable and fruits, are used for human consumption. Therefore, an understanding of the leaching behavior of As in surface soils is of high importance, because such behavior may increase the bioavailability of As in the soil horizon. In this study, we have investigated the role of phosphate ions in leaching and bioavailability of As in the soil horizon, where drinking groundwater contains elevated levels of As (≥50 μg/L). Soil and groundwater samples were characterized in the laboratory and measured for physical and chemical constituents. The soils are generally neutral to slightly alkaline in character (pH range 7.5–8.1) with low to moderate levels of free Fe₂O₃, Al₂O₃, CaCO₃, organic carbon, and clay content. The measured electrical conductivity (mean 599 μS/cm) of the soils demonstrates their non-saline nature. The Eh values (range −37 to −151 mV) of the groundwater indicate anoxic condition with low to moderate levels of bicarbonate (range 100–630 mg/L) and phosphate (range 0.002–4.0 mg/L). The arsenic content (range 50–690 μg/L; mean 321 μg/L) in groundwater has exceeded both WHO recommended guideline values (10 μg/L) and the National safe drinking water limit (50 μg/L). Regression analyses demonstrate that the bioavailability of As in the soil horizon is mainly controlled by the composition of free Fe₂O₃ and CaCO₃ content of the soils. However, application of P could increase bioavailability of As in the soil horizon and become available to plants for uptake.     

Source and dispersal of suspended sediment in the macro-tidal Gulf of Kachchh

The macro-tidal Gulf of Kachchh, covering nearly 7000 km(2), is located about 150 km south of the Indus River mouth. In spite of semi-arid climate and lack of major rivers flowing into it, the Gulf is highly turbid with suspended sediment concentrations (SSC) during October-November 2002 ranging between 0.5 and 674 mgl(-1). Highly turbid waters are observed towards the northern portion of the mouth of the Gulf, at the head of the Gulf and adjacent to the numerous shoals present within the Gulf. Perennial high SSC in the Gulf is due to resuspension of sediments by strong tidal currents, shallow bathymetry and presence of fine-grained sediments on the sea floor. Numerical model studies show that there is a dynamic barrier in the central Gulf, which prevents the exchange of water and suspended sediments between the outer and inner Gulf. This dynamic barrier associated with strong east-west tidal currents restricts the turbid waters mainly to the northern Gulf, resulting in relatively clear waters (SSC<10 mgl(-1)) in the southern and central portions of the Gulf. Laser particle size distribution, clay mineralogy and geochemistry of the suspended matter show that the main source of sediments to the Gulf of Kachchh is the Indus River. Although the Indus discharge has been severely curtailed in the recent decades due to construction of numerous dams and barrages, the Gulf of Kachchh continues to receive resuspended sediments from the numerous meso and macro-tidal creeks of the Indus delta. The sediments at the head of the Gulf appear to be a mixture of sediments derived from the Indus as well as the numerous seasonal rivers draining the Rann of Kachchh.     

Propagation of a strong cylindrical shock wave in a rotational axisymmetric dusty gas with exponentially varying density

Non-similarity solutions are obtained for one-dimensional isothermal and adiabatic flow behind strong cylindrical shock wave propagation in a rotational axisymmetric dusty gas,which has a variable azimuthal and axial fluid velocity.The dusty gas is assumed to be a mixture of small solid particles and perfect gas.The equilibrium flow conditions are assumed to be maintained,and the density of the mixture is assumed to be varying and obeying an exponential law.The fluid velocities in the ambient medium are assumed to obey exponential laws.The shock wave moves with variable velocity.The effects of variation of the mass concentration of solid particles in the mixture,and the ratio of the density of solid particles to the initial density of the gas on the flow variables in the region behind the shock are investigated at given times.Also,a comparison between the solutions in the cases of isothermal and adiabatic flows is made.     

Image processing applications for customized mining and ore classification

During the mining operation, ore sorting and directing different grade ores to different processing circuits is a manual task in most of working mines, but this work puts a step forward toward automation of this process. The radical development in the area of image and data processing allows speedy processing of the full color digital images for the preferred investigations. In this paper, an approach has been proposed to classify the ores for blast furnace feed, based on the visual texture of the ore particles. The visual texture of ore particles vary with the mineral contents, for example, blue dust, hard ore, soft ore, etc. This information can be quantified by using image processing technique in red, green, and blue color space and first- and second-order statistical analysis. Commonly used Hartlics textural features were calculated along with red, green, and blue color values for 5?×?5-pixel size windowpanes extracted from five separate images. Results obtained show encouraging accuracy to apply the approach to develop an expert system for online ore quality monitoring to control the ore blending in the feed ore circuits as well as separating gangue minerals present in the feed ores. Matlab 6.5 was used for visual textural analysis and classification.