
 The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Ground Motion Characteristics Estimated from Spectral Ratio between Horizontal and Verticcl Components of Mietremors.

Groundwater is one of the most valuable natural resources, which supports human health, economic development and ecological diversity. Overexploitation and unabated pollution of this vital resource is threatening our ecosystems and even the life of future generations. With the advent of powerful personal computers and the advances in space technology, efficient techniques for land and water management have evolved of which RS (remote sensing) and GIS (geographic information system) are of great significance. These techniques have fundamentally changed our thoughts and ways to manage natural resources in general and water resources in particular. The main intent of the present paper is to highlight RS and GIS technologies and to present a comprehensive review on their applications to groundwater hydrology. A detailed survey of literature revealed six major areas of RS and GIS applications in groundwater hydrology: (i) exploration and assessment of groundwater resources, (ii) selection of artificial recharge sites, (iii) GIS-based subsurface flow and pollution modeling, (iv) groundwater-pollution hazard assessment and protection planning, (v) estimation of natural recharge distribution, and (vi) hydrogeologic data analysis and process monitoring. Although the use of these techniques in groundwater studies has rapidly increased since early nineties, the success rate is very limited and most applications are still in their infancy. Based on this review, salient areas in need of further research and development are discussed, together with the constraints for RS and GIS applications in developing nations. More and more RS- and GIS-based groundwater studies are recommended to be carried out in conjunction with field investigations to effectively exploit the expanding potential of RS and GIS technologies, which will perfect and standardize current applications as well as evolve new approaches and applications. It is concluded that both the RS and GIS technologies have great potential to revolutionize the monitoring and management of vital groundwater resources in the future, though some challenges are daunting before hydrogeologists/hydrologists.

Groundwater management and development by integrated remote sensing and geographic information systems: prospects and constraints

Though drought is a recurrent phenomenon in Bangladesh, very little attention has been so far paid to the mitigation and preparedness of droughts. This article presents a method for spatial assessment of drought risk in Bangladesh. A conceptual framework, which emphasizes the combined role of hazard and vulnerability in defining risk, is used for the study. Standardized precipitation index method in a GIS environment is used to map the spatial extents of drought hazards in different time steps. The key social and physical factors that define drought vulnerability in the context of Bangladesh are identified and corresponding thematic maps in district level are prepared. Composite drought vulnerability map is developed through the integration of those thematic maps. The risk is computed as the product of the hazard and vulnerability. The result shows that droughts pose highest risk to the northern and northwestern districts of Bangladesh.

Drought risk assessment in the western part of Bangladesh

Velocity-model building is a key step in hydrocarbon exploration. The main product of velocity-model building is an initial model of the subsurface that is subsequently used in seismic ima...

Deep-learning tomography

Remote sensing (RS) and geographic information system (GIS) are promising tools for efficient planning and management of vital groundwater resources, especially in data-scarce developing nations. In this study, a standard methodology is proposed to delineate groundwater potential zones using integrated RS, GIS and multi-criteria decision making (MCDM) techniques. The developed methodology is demonstrated by a case study in Udaipur district of Rajasthan, western India. Initially, ten thematic layers, viz., topographic elevation, land slope, geomorphology, geology, soil, pre- and post-monsoon groundwater depths, annual net recharge, annual rainfall, and proximity to surface water bodies were considered in this study. These thematic layers were scrutinized by principal component analysis technique to select influential layers for groundwater prospecting. Selected seven thematic layers and their features were assigned suitable weights on the Saaty’s scale according to their relative importance in groundwater occurrence. The assigned weights of the thematic layers and their features were then normalized by using AHP (analytic hierarchy process) MCDM technique and eigenvector method. Finally, the selected thematic maps were integrated by weighted linear combination method in a GIS environment to generate a groundwater potential map. Thus, four groundwater potential zones were identified and demarcated in the study area, viz., ‘good’, ‘moderate’, ‘poor’ and ‘very poor’ based on groundwater potential index values. The area falling in the ‘good’ zone is about 2,113 km2 (17% of the total study area), which encompasses major portions of Sarada, Salumber, Girwa, Dhariawad, and Mavli blocks of the study area. The northeast and southwest portions along with some scattered patches fall in the ‘moderate’ zone, which encompasses an area of 3,710 km2 (about 29%). The ‘poor’ zone is dominant in the study area which covers an area of 4,599 km2 (36% of the total area). The western portion and parts of eastern and southeast portions of the study area are characterized as having ‘very poor’ groundwater potential, and this zone covers an area of 2,273 km2 (18%). Moreover, in the ‘good’ zone, the mean annually exploitable groundwater reserve is estimated at 0.026 million cubic metres per km2 (MCM/km2), whereas it is 0.024 MCM/km2 in the ‘moderate’ zone, 0.018 MCM/km2 in the ‘poor’ zone, and 0.013 MCM/km2 in the ‘very poor’ zone. The groundwater potential map was finally verified using the well yield data of 39 pumping wells, and the result was found satisfactory.

Assessment of Groundwater Potential in a Semi-Arid Region of India Using Remote Sensing, GIS and MCDM Techniques

A Geographical Information System (GIS) integration tool is proposed to demarcate the groundwater potential zone in a soft rock area using seven hydrogeologic themes: lithology, geomorphology, soil, net recharge, drainage density, slope and surface water bodies. Except for net recharge and slope, the other five themes are derived from remote sensing data. IRS-1B LISS-II data was used for a 631 km2 area in Midnapur District, West Bengal, India. While slope was calculated using topographic sheets, net recharge was obtained from annual water table fluctuation data. Each feature of all the thematic maps was evaluated according to its relative importance in the prediction of groundwater potential. The evolved GIS-based model of the study area was found to be in strong agreement with available borehole and pumping test data.

Groundwater potential modelling in a soft rock area using a GIS

Online material : Data files for seismogenic source zones (polygons), smoothed-gridded seismicity models, and hazard curves at 0.2° regular grid spacing over the study region.

Earthquake disasters occur mainly due to the collapse of buildings and structures triggered by ground motions. It is, therefore, important to predict ground-shaking levels in order to determine appropriate building code provisions for earthquake-resistant design of structures. This involves extensive analyses and development of appropriate seismological models; namely, seismogenic sources, seismic site conditions, and ground motion predictions. The hazard products, viz . data and maps, constitute important tools for framing public policies toward land-use planning, building regulations, insurance, and emergency preparedness.

View this table:

Table 1 
Major Earthquake Casualties during 1900–2008 in India and Adjoining Regions



In India, several events during the last 100 years, as listed in Table 1, indicate that even moderate earthquakes ( MW < 7.0) can cause significant devastation. On one hand, ongoing urbanization and unprecedented population growth have considerably aggravated the prevailing seismic risk. On the other hand, the available seismic hazard maps covering the entire country are about a decade old. Consequently an updated seismic hazard model for the country is imperative and necessitated by new data, recent findings, and methodological improvements. In the present study, we make a case for new probabilistic seismic hazard analysis (PSHA) of India. The fundamental studies have been carried out to deliver the hazard components, including seismogenic source zonation and seismicity modeling in the Indian subcontinent (Thingbaijam and Nath 2011), assessment of site conditions across the country (Nath, Thingbaijam, Adhikari et al. 2011), and a suitability test for the ground-motion prediction equations in the regional context (Nath and Thingbaijam 2011). These components are integrated to deliver a preliminary model consisting of spatial distributions of peak ground acceleration (PGA) and 5%-damped pseudo spectral acceleration (PSA).

Initial attempts at …

/pdf/probabilistic-seismic-hazard-assessment-of-india-46hsn804y2.pdf

Probabilistic Seismic Hazard Assessment of India

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.

Recent seismicity in Northeast India and its adjoining region

A comprehensive analytical as well as numerical treatment of seismological, geological, geomorphological and geotechnical concepts has been implemented through microzonation projects in the northeast Indian provinces of Sikkim Himalaya and Guwahati city, representing cases of contrasting geological backgrounds — a hilly terrain and a predominantly alluvial basin respectively. The estimated maximum earthquakes in the underlying seismic source zones, demarcated in the broad northeast Indian region, implicates scenario earthquakes of M
 W
 8.3 and 8.7 to the respective study regions for deterministic seismic hazard assessments. The microzonation approach as undertaken in the present analyses involves multi-criteria seismic hazard evaluation through thematic integration of contributing factors. The geomorphological themes for Sikkim Himalaya include surface geology, soil cover, slope, rock outcrop and landslide integrated to achieve geological hazard distribution. Seismological themes, namely surface consistent peak ground acceleration and predominant frequency were, thereafter, overlaid on and added with the geological hazard distribution to obtain the seismic hazard microzonation map of the Sikkim Himalaya. On the other hand, the microzonation study of Guwahati city accounts for eight themes — geological and geomorphological, basement or bedrock, landuse, landslide, factor of safety for soil stability, shear wave velocity, predominant frequency, and surface consistent peak ground acceleration. The five broad qualitative hazard classifications — ‘low’, ‘moderate’, ‘high’, ‘moderate high’ and ‘very high’ could be applied in both the cases, albeit with different implications to peak ground acceleration variations. These developed hazard maps offer better representation of the local specific seismic hazard variation in the terrain.

Earthquake hazard in Northeast India - A seismic microzonation approach with typical case studies from Sikkim Himalaya and Guwahati city

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.

Sankar Kumar Nath

Papers

Groundwater potential modelling in a soft rock area using a GIS

Probabilistic Seismic Hazard Assessment of India

Recent seismicity in Northeast India and its adjoining region

Earthquake hazard in Northeast India - A seismic microzonation approach with typical case studies from Sikkim Himalaya and Guwahati city

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