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.     

Long-term orbit computations with KS uniformly regular canonical elements with oblateness

This paper concerns with the study of KS uniformly regular canonical elements with Earth's oblateness. These elements, ten in number, are all constant in the unperturbed motion and even in the perturbed motion, the substitution is straightforward and elementary due to the transformation laws being explicit and closed expression. By utilizing the recursion formulas of Legendre's polynomials, we are able to include any number of Earth's zonal harmonics J _n in the package and also economize the computations. A fixed step-size fourth-order Runge-Kutta-Gill method is employed for numerical integration of the canonical equations.Utilizing 5 test cases covering a large range of semimajor axis and eccentricity, we have carried out computations to study the effects of Earth's zonal harmonics (up to J ₃₆) and integration step-size variation. Bilinear relations and energy equation are used for checking the accuracies of numerical integration. From the application point of view, the package is utilized to study the behaviour of 900 km height near-circular sun-synchronous satellite orbit over a longer duration of 220 days time (nearly 3078 revolutions) and the necessity of including more number of Earth's zonal harmonic terms is noticed. The package is also used to study the effect of higher zonal harmonics on three 900 km height near-circular orbits with inclinations of 60, 63.2, and 65 degrees, by including Earth's zonal harmonics up to J ₂₄. The mean eccentricity (e _m) is found to have long-periods of 459.6, 6925.1 and 1077.6 days, respectively. Sharp changes in the variation of _m near the minima to e_m are noticed. The values of _m are found to be very near to +-90 degrees at the extrema of e_m. The same orbit is employed to study the effect of variation of inclination from 0 to 180 degrees on long-period (T) of eccentricity with J ₂ to J ₂₄ terms. T is found to increase rapidly as we proceed towards the critical inclinations.     

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.     

http://www.sciencedirect.com/science/article/pii/S1674987112000254

The applications of intelligent techniques have increased exponentially in recent days to study most of the non-linear parameters.In particular,the behavior of earth resembles the non-linearity applications.An efficient tool is needed for the interpretation of geophysical parameters to study the subsurface of the earth.Artificial Neural Networks(ANN) perform certain tasks if the structure of the network is modified accordingly for the purpose it has been used.The three most robust networks were taken and comparatively analyzed for their performance to choose the appropriate network.The single-layer feed-forward neural network with the back propagation algorithm is chosen as one of the well-suited networks after comparing the results.Initially,certain synthetic data sets of all three-layer curves have been taken for training the network,and the network is validated by the Held datasets collected from Tuticorin Coastal Region(78°7′30″E and 8°48′45″N),Tamil Nadu.India.The interpretation has been done successfully using the corresponding learning algorithm in the present study.With proper training of back propagation networks,it tends to give the resistivity and thickness of the subsurface layer model of the field resistivity data concerning the synthetic data trained earlier in the appropriate network.The network is trained with more Vertical Electrical Sounding(VES) data,and this trained network is demonstrated by the field data.Groundwater table depth also has been modeled.     

Petrographic characteristics of the Proterozoic Vempalle carbonates,Cuddapah Basin,India and their implications

The Vempalle Formation of the Proterozoic Cuddapah basin has a well developed sequence of carbonate rocks, which are interbedded with shales, siltstones and chert. The stromatolitic carbonates are conspicuous at many places but the oolitic carbonates are less prominent and are present only in some areas. All the carbonates are pervasively dolomitized. Petrographic examination of these carbonates revealed that they are predominantly made up of fine grained micrite with patchy development of sparite and chert/quartz. The stromatolitic carbonates show distinct banding of alternate carbonate and cherty layers. The latter are rich in organic matter indicating prevalence of profuse biogenic activity. The oolitic carbonates comprise of ooids showing both concentric and radial patterns and made up of carbonate/chert and cemented by micro/mega quartz or carbonate itself. Diagenetic and post depositional features are reflected in cementation, recrystallization, compaction, stylolite formation and silicification processes. Various stages of cementing material are observed. Secondary vein fillings of carbonate or quartz traverse the carbonate/cherty groundmass. Intraclasts present suggest occasional erosional destruction of associated sediments, short lived transport and local redeposition. Accessory silicate minerals represent terrigenous influx during deposition. Dolomitization of the carbonates was fabric retentive and early diagenetic. The environmental conditions were characterised by low energy, within a shallow water zone, in occasional higher energy events and turbulence. The carbonates appear to have been deposited on a shallow water ramp within a tidal regime.     

Delineation of fresh aquifers in tannery belt for sustainable development — A case study from southern India

The tannery effluents discharged by the existing units on either side of the Palar river at Ambur town (known for tannery industry), has resulted in vertical and lateral spread of pollution. The study area of 55.3 km² is situated on a granitic terrain of Archaean age with undulating topography and hillocks. The shallow aquifers, in flood plain and valley fills of the river are highly polluted (with EC: 15340 μS/cm) by tannery effluents making groundwater unfit for any use, hence the local population (20000) face health hazards and shortage of potable water. Hydrogeological, geophysical and in-situ groundwater quality measurement were carried out to demarcate fresh groundwater zones and to delineate lateral and vertical extent of pollution. The results show, brackish aquifer was characterized by low order of resistivity (<20 Ω-m) with a thickness of 8.5 to 28 m located in the flood plains, valley fills, and partially in hard rock formations, whereas the fresh water aquifer resistivity varying from 23 to 216 Ω-m in hard rock. Further, these results were correlated with the water quality data and Ground Penetrating Radar (GPR) signals. The integrated studies revealed that pollution due to tannery effluents has spread over an area of 33.4 km² (60.4 %) on either side of the river and only a small area of 21.9 km² (39.6 %) was identified as fresh groundwater zone, which has to be conserved and exploited in sustainable manner for future generations.     

Mapping groundwater quality for irrigation in Punjab, North-West India, using geographical information system

The state of Punjab—a part of the Indus basin of the Indian subcontinent has an excellent net work of irrigation facilities. However, due to intensive cultivation it is facing a major problem with respect to quality of groundwater for irrigation. In the present investigation, geo-referenced groundwater samples were analysed to map water quality using geographical information system. Electrical conductivity varied from 0.418 to 5.754 dS m^?1 with an average of 1.365 dS m^?1. The carbonate ranged between 0 and 120 mg L^?1, whereas bicarbonate ranged from 5 to 1,000 mg L^?1. Chloride varied from 7 to 2,347 mg L^?1. Calcium plus magnesium ranged from 12 to 1,216 mg L^?1 with a mean value of 169 mg L^?1. Sodium adsorption ratio ranged between 0.0 and 34.78 with an average of 2.66 meq L^?1/2. Residual sodium carbonate varied from 0 to 21.30 meq L^?1 with a standard deviation of 2.24. The Geographic Information System (GIS)-based mapping indicated that water in suitable category spatially covered 45.7 % of the state which is located mostly in the sub-mountain (Siwalik Hills), north-eastern undulating and piedmont and alluvial plain agro-eco-subregions. Marginally suitable groundwater spatially covered 46.1 % in the central alluvial plain and south-western alluvial plain agro-eco-subregions. Unsuitable groundwater covered 8.2 % of the state, mostly in the erstwhile sodic soils areas in the central alluvial plain and south-western alluvial plain agro-eco-subregions. GIS-based maps are effective in identifying hot spots which need immediate attention and call for strategic planning for sustainable management.     

Rain-triggered slope failure of the railway embankment at Malda,India

The common slope stability analysis is incapable of accurately forecasting shallow slides where suction pressures play a critical role. This realization is used for elaborate stability analyses which include soil suction to better predict rainfall-induced slides at railway embankment at Malda where three known cases of slope failures and train derailments occurred after heavy rainfall. The relationship between the soil–water content and the matric suction is established for the embankment soil. It is then used in the coupled analyses of seepage and slope stability to estimate performances of the embankment at different intensity and duration of rainfall. The numerical simulations are performed with the FE code Geo-Studio. The numerical results show significant reduction in the factor of safety of the railway embankment with the increase in the intensity and duration of rainfall. The effectiveness of the proposed mitigation measures including placement of 2 m-wide free draining rockfill across the slopes and drilling 5-m-long sheet pile wall at the toe of the embankment is studied numerically. The study confirms that the proposed mitigation measures effectively increase the factor of safety of the embankment and stabilizing it even in case of a heavy rainfall of 25 mm/h over 12 h.     

Analysis of Flexible Pavements Reinforced with Geogrids

Effectiveness of glass fiber grids as a reinforcement of the asphalt layer in a flexible pavement system was investigated. The study involved both laboratory experimental work and computer analysis of pavement sections. Twenty flexible pavement sections (with and without glass fiber grids) were constructed and tested in the laboratory as a part of the experimental study. The laboratory-scale pavement sections were instrumented with pressure cells, displacement gages, and strain gages. Test sections were subjected to 1,000,000 load applications at a frequency of 1.2 Hz. Static loading tests were conducted at intervals of 100,000 load applications. In thirteen experiments, glass fiber grids were used as reinforcement in the asphalt layer. Several computer analyses of flexible pavement sections were performed by using the finite element method (FEM). The laboratory data were compared with results obtained from the computer analyses. Results from this study show that glass fiber grids can be used to improve the performance of flexible pavement systems. It was also observed that the inclusion of glass fiber grid in the asphalt layer provided resistance to crack propagation. Overall, the flexible pavement sections reinforced with glass fiber grids showed better performance under laboratory test conditions.     

Numerical analysis of soil pipe effects on hillslope water dynamics

Soil pipes are considered to drain off water from a hillslope and play an important role in the subsurface runoff generation process, thus reducing the slope failure susceptibility. However, soil pipes are also often detected on the collapsed slope suggesting that they might act to induce slope instability. To examine how the soil pipes act on pore-water pressure generation and on a slope failure processes, a numerical model was developed. The model was used to test the response of pore-water pressure in a hillslope with soil pipes of different cross-sectional areas, lengths, distances from the impermeable bed, roughness, and hillslope angles. The model was also tested to find the response of open soil pipe if blocked. The study reveals that pipes reduce pore-water pressure (measured closed to bed) around its upstream end and increase around its downstream end if compared with no pipe case. Pore-water pressure at downstream end is increased with increase in hillslope angle, pipe cross-sectional area, pipe length, or depth of soil pipe. Soil pipe, even if it is ended within the hillslope, increases the total discharge from hillslope. Location of rough soil also affects the discharge and pressure within the hillslope. If the less rough pipe is close to the source of water, discharge from hillslope matrix is greater regardless of its downstream pipe roughness. Blockage of small portion of open soil pipe increases the soil pressure around the region but not beyond the case if there is no soil pipe. However, complete collapse of soil pipe from a point to all along the downstream end of hillslope increases the pore-water pressure beyond the pressure if there were no soil pipes. Therefore, the position and type of soil pipe collapse might play an important role in shallow landslide initiation.