ISSN: 2277-5536 (Print); 2277-5641 (Online) DAV International Journal of Science Volume-1, Issue-2 June, 2012 40 EXTRACTION OF MORPHOTECTONIC FEATURES USING DEM AND TERRAIN GENERALISATION ON THE AREA AROUND LANJA, DISTRICT RATNAGIRI, INDIA. Dikshit V.M. and Patil B.S. D.B.F. Dayanand College of Arts and Science, Solapur, Maharashtra, India. ABSTRACT The present study aims to use Digital Terrain Analysis to extract major morphotectonic features from DEM of the study area. The methodology is based on generation of colour coded DEM and terrain generalization to identify morphotectonic features and associated phenomena. The colour coded DEM was generated with the help of SRTM data. Terrain generalization algorithm was applied to DEM to reduce the noise formed by insignificant details which in turn enhances the major morphotectonic features. These techniques are found to be helpful to recognize and demarcate major geomorphic domains, linear and curvilinear lineaments, ridge lines, valley forms along with triangular facets. KEY WORDS: Digital Elevation Model, Digital Terrain Modeling, Terrain Generalization. INTRODUCTION Digital Elevation Model (DEM) represents the spatial distribution of elevations above some arbitrary datum in a landscape, whereas, Digital Terrain Model (DTM) is an ordered arrays of numbers that represent the spatial distribution of terrain attributes (Moore et al. 1993). DEM provide an image of bare land surface and yield digital terrain information not fuzzy by land cover features and hence, allow characterization of land surface quantitatively in terms of slope, gradient and curvature. Digital Terrain Analysis (DTA) can be implemented on digital elevation model in order to derive various terrain attributes (Jordan and Peckham, 2007). In this study, DTA has been carried out by means of the combined use of: 1) elevation analysis with the colour coded DEM and 2) terrain generalization to identify major morphotectonic features for tectonic interpretation. Morphotectonic features represented by digital elevation models of the Lanja area, district Ratnagiri, Maharashtra, were extracted, described and interpreted in terms of geomorphology and morphotectonics. The analysis of multi-source data was implemented by means of GIS operations. Study area: Lanja region, district Ratnagiri, from Konkan plains of Maharashtra is part of northern section of western passive continental margin of India. Its major morphotectonic features from west to east are coast line, Konkan Coastal Belt (KCB) and Western Ghat Scrap (WGS) (Fig. 1). The KCB is distinct morphotectonic feature, whose average width is about 50km. Geomorphologically this belt exhibits numerous small and short butte and mesas at different altitudes near the coast line and further east it suddenly rises to great heights forming scrap facing towards west. The region is traversed by numerous westerly flowing rivers. The Konkan plains north of 16 0 30‟ N latitude and the main Maharashtra plateau east of WGS are covered by horizontally disposed basaltic lava flows of Deccan Traps of Upper Cretaceous to Eocene age. The significant processes related to the effusion of flood basalts are the northward movement of Indian plate over the Reunion Hotspot resulting crustal arching, rifting and down faulting of western arm of the rift (Cambell and Griffith, 1990; Radhakrishnan, 1993). The basement of southern traps is composed of heterogeneous stratigraphic formations which mainly include Dharwar Supergroup, Kaladgis and Bhima Groups and spans about 3000 million years of the earth‟s history. The KCB is the major belt of tectonic disturbance and it has experienced few numbers of seismic events of moderate magnitude (Naini and Talwani, 1983). It is characterized by strong concentration of lineaments in an approximately N- S, NW-SE and NE-SW directions (Powar, 1980 and 1993). The NW-SE trending major lineaments in the southern Deccan Traps coincides the structural trends in the basement exposed at its south and hence indicate these are as the results of rejuvenation of weak zones or faults in the basement. According to Widdowson and Mithchel (1999), the major lineaments along which the pattern of modern drainage is controlled are possibly an expression of extensive fracturing or small scale faulting and their details are not clear. Data used and methodology DEM preparation: The Shuttle Radar Topography Mission (SRTM) elevation data on a near-global scale was used to generate high-resolution digital topographic database. Filled and finished data of 3arc second WRS-2 of 90m resolution has been downloaded from the GLCF site. Two tiles of height data of WRS-2 was used for the further preprocessing and generation of DEM. The tiles were mosaiced and image subset of study area was clipped from the whole scene. The gaps in data were filled and negative values and oceans were removed in ArcGIS environment. The SRTM data (90m resolution) was then converted into grids 30m resolution with the help of bicubic polynomial interpolation algorithm (Keeratikasikorn and Trisirisatayawong, 2008). The procedure for converting raw SRTM data to DEM was adapted as suggested by Borut Vršcaj et al., 2007 and present ed in the form of colour coded map (Fig. 2).