S M Ramasamy
Professor and Head
Centre for Remote Sensing
Bharathidasan University, Tiruchirappalli, India
C J Kumanan
J Saravanavel and C Anandan
Jr Research Fellow
Centre for Remote Sensing,
Bharathidasan University, Khajamalai Campus
The geospatial technology has emerged as a credible tool in various natural disaster management. This paper demonstrates the same with some real time case studies conducted using IRS 1C/1D imagery and Arc Info based GIS in the aspects of seismic, landslide and flood hazards from South India
The natural disasters have become fast recurring phenomenon all over the world causing greater concern and damage to the man and his properties. While the disasters like earthquakes, volcanic eruptions, flooding, cyclones, forest fire, etc., are mostly tutored by the dynamically active Earth and the atmosphere, the disasters like landslides, soil erosion, reservoir siltation, salt water intrusion into the sweet coastal aquifers, sand advance in the desert, soil salinity etc, are by and large appear to be due to improper interaction of the humans with Earth ecosystems. Whether these are natural or the human triggered disasters, the time has come to make preventive and if possible, predictive models and management plans. Such disaster management plans need critical understanding on the type of natural disasters and the causative factors, so that optimal demand driven management plans could be drawn. The present article briefly narrates some real time case studies from South India as how the Remote Sensing technology, owing to its synoptivity, multispectral possibility and repeativity and the GIS due to its advanced virtues of creating multi base and integrated spatial data bases can help in preparing the disaster zonation maps and the management plans fastly and precisely.
The southern part of the Indian peninsular has been thought as inert to younger earth movements and the related seismicities for the past several decades. However, many geo-scientists have recorded observations for the possible time transgressive tectonic movements since Jurassic period (210-140 million years) in different parts of South India falling in Mangalore-Chennai-Cape Comorin triangle (Arogyasamy 1963, Radhakrishnan 1993, Vaidyanathan 1967, Suryanarayanan and Prabakhar Rao 1981, Nair and Subramanian 1989, Ramasamy and Balaji 1995, Valdiya 1998 and many others). But, the geoscientists were not very much convinced about the seismic vulnerability of peninsular India until the massive earthquake devastated the Killari region recently. Since then, the geoscientists have started paying more attention in understanding the seismic vulnerability of South India. In the aspects of seismicity, in general, there has been a greater consensus amongst the scientists that the weaker tectonic zones act as loci for the seismic reactions. As far as South India is concerned, the lineament map prepared by Ramasamy et al. (1987) for parts of South India has lead to the detection of four sets of Precambrian lineaments (3500 m.y.) with ENE-WSW extensional, NE-SW dextral, NW-SE sinistral and NNW-SSE release fractures, all related to the Precambrian orogeny. But Ramasamy and Balaji (1995) and Ramasamy (2004), on the basis of the mega structures / lineaments and the various geomorphological anomalies observed in IRS imagery, have observed that the area along Managalore-Chennai and Cochin-Ramanathapuram are arching up with an intervening land subsidence along Ponnani-Manamelgudi during the Pleistocene – recent period. Such ongoing buckling was attributed to the still prevalent northerly directed compressive force related to the post-collision tectonic phenomenon. These workers have further observed that the N-S faults are opening up like lenses, NE-SW trending faults are sinistrally moving, NW-SE trending faults are dextrally moving and E-W trending fracture swarms are opening up as release fractures due to such post-collision phenomenon.
Under this tectonic scenario, the present Remote Sensing and GIS based studies were conducted to map the seismogenic corridors of South India. For the same all tectonic lineaments were mapped in detail using IRS 1C/1D satellite data for South India, falling south of 14o North latitude (Mangalore-Chennai-Cape Comorin triangle). From the lineament map, the lineament density diagram was prepared by counting the total length of the lineaments for 729 grids of 400 sq.km each, plotting them in the grid centers and contouring them. From such lineament density contours, maxima axes were drawn along the crests of the elliptical contours of maxima values. Similarly, earthquake epicenter data were collected for over 473 locations from historical seismicity data (Ramalingeswara Rao 1992) and the total numbers of earthquake epicenters falling in the same 729 grids were counted, contoured and thus isoseismal lines were drawn. From such contours the isoseismic maxima axes were drawn along the crests of the elliptical contours of maximum values.
Such lineament density maxima axes and isoseismal maxima axes drawn from the respective contours were brought on to a single digital overlay using ArcGIS (Fig. 1). Such conjunctive analysis between both the maximas has indicated that, in parts of central Tamil Nadu, there observed a parallelism between N-S trending lineament maxima and the isoseismal maxima (A, Fig. 1). On the contrary, in the Western Kerala and Karnataka regions, especially in Ponnani-Mangalore sector (B, Fig. 1), there is a strong parallelism between NE-SW lineament maximas and isoseismal maximas. In the southern part of Tamil Nadu (C, Fig. 1) the NW-SE trending lineaments appear to coincide with isoseismal maximas. Whereas in the northern Chennai region (D, Fig. 1), the isoseismal maximas show a directional agreement with E-W lineament maximas. Thus, such Remote Sensing and GIS based appraisal has indicated broader domains and corridors of seismicites along N-S trending lineaments in central Tamil Nadu, NE-SW lineaments in parts of Kerala and Karnataka, NW-SE lineaments in Southern most tip of South India and along E-W fracture swarms in Chennai region. Such zones have been buffered out and shown as probable seismogenic faults of South India. Though detailed studies are warranted to bring out a more clear picture on the seismicity of South India, this spatial data will certainly provide baseline information for further seismological studies. Such geospatial outputs can be used as guidelines for drawing up management plans for minimizing its effects, by avoiding heavy structures and optimal groundwater management etc.