Abstract
This article endeavours to analyse the recent deformation in the Enfidha region. This analysis has been carried out using the Residual Digital Elevation Model (DEM). It is the altimetric difference between two DEM generated from the contour lines of two topographical maps over a period of 100 years. This deformation has been studied by some authors who report the presence of recent ground movements by comparing contour lines with a downward trend in elevation from 1893 to 1985. In 2006, this study area was marked by the presence of two earthquakes that occurred in several coastal cities located in the northeastern part of Tunisia. Our study involves a quantitative estimation of altimetric variations under a Geographic Information System (GIS) environment. Our proposed methodology aims at the mapping of residual (DEM) and the extraction of parameters that have a morphological and morphostructural signature. The extraction of quantitative morphostructural parameters requires the integration of multi-source and multi-scale data. This can only be done if the problem of heterogeneity at the level of scale and coordinate system is solved through the use of GIS tools and the obtainment of the vectorial shapefile format. Then, in order to compare the DEM generation errors with reference to recent and old data, they must be projected in the same projection system and on the same scale. The available data are two topographic maps of Enfidha which represent two different epochs. The first one is an old topographic map of 1893 (type 1922) at a scale of 1:50,000 and the second one is a recent topographic map of 1985 at a scale of 1:25,000. These topographical maps have the Lambert (IGN) projection system. This methodological approach, based on residual (DEM), allows to highlight an estimated subsidence of 3 m/100years located in the Enfidha plain and extends to the south coast of Cap Bon area in Tunisia. The variation of the contour lines shape between the old and the recent map can be studied in correlation with a relay structure fault observed and recognized by some analysts in this area. These relay accidents remain active according to the results obtained by the residual (DEM) and validated by the field observations of two sites that we have carried out in the Enfidha endorheic basin.
Highlights
Since the early orogenic phases, the Tunisian Sahel region and its foreland have recorded distinct cycles of uplift, erosion and displacement estimated displacement estimated in some regions at a few hundred metres [1] [2]
The various studies carried out using morphometric index and structural analyses [10]-[21] indicate that the Digital Elevation Model (DEM), the hydrographic network can significantly determine the existence of tectonics or erosion
This study focuses on the implementation of a methodological approach (Figure 3) based essentially on both the use of digital topographic data and the generation of DEM in a Geographic Information System (GIS) environment
Summary
Since the early orogenic phases, the Tunisian Sahel region and its foreland have recorded distinct cycles of uplift, erosion and displacement estimated displacement estimated in some regions at a few hundred metres [1] [2]. This work has four main objectives: 1) to measure, using morphometric indices, the amplitude of the movements responsible for the collapse of the endorheic basin of the Enfidha region 2) to develop a morphological pattern in line with that of the tectonics of the region 3) to present an evolutionary scenario of this region compatible with the general geodynamic framework of the Atlasique Tunisie 4) and to relate this evolution with that observed in the western Mediterranean during the quaternary period [8] [9] To achieve these objectives, we have collected data from the analysis of a Digital Elevation Model (DEM) of two topographic maps with two different periods from 1893 (type 1922) at the 1/50,000 scale and from 1985 at the 1/25,000 scale with the Lambert (IGN) projection system. It is based on the residual (DEM), which corresponds to an arithmetical difference of two DEM
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