APPLICATION DE LA TELEDETECTION DANS LA CARTOGRAPHIE DES RISQUES GEOLOGIQUES Sahra AOURARI & Djilali BOUZIANE &Djamel MACHANE

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1 APPLICATION DE LA TELEDETECTION DANS LA CARTOGRAPHIE DES RISQUES GEOLOGIQUES Sahra AOURARI & Djilali BOUZIANE &Djamel MACHANE CGS: Algerian Centre of Research Applied in Earthquake Engineering 01 Kaddour Street BP 252 Hussein Dey - Algeries Algeria Abstract: The study is an example of mapping used in seismic hazard assessment. It concerns the use of aerials photographies, satellites views for the detection of active tectonic structures in seismic areas of the North Algeria where the earthquakes represent the most threatening hazards. In fact, many regions of this part of the country have endured destructive earthquakes causing casualties and material damage. Keywords: Remote sensing, DEM (digital elevation models), morphotectonic Escarpment, active fault, seismic hazard, seismic risk. Introduction The remote sensing is the set of knowledge and techniques used for determining the features of the atmosphere and the surface of the Earth, from measurements taken from an airplane, satellite or a space shuttle, that evolving at a suitable distance from the Earth. Geomatics whose principle is devoted to technical of digital photogrammetry, treatment of satellites images and also the establishment of databases and geographical thematic. The digital elevation models (DEM) achieved in the seismic hazard field and are providing detailed maps which are produced by the combination of topography, geology and the seismicity. Uses of the satellites imagery Data processing is done using software on a desktop computer. The first stage of the operation consists in the reconstruction of the relief of the survey zone. The Raster and vector data (coordinates X, Y, Z) are imported from Worldwide SRTM Elevation Data (3-arc-second resolution) [Global map] (Fig.1).

2 Figure 1: Restitution elevation data and generation contours from SRTM data The data is then transferred to a geographic information system (GIS Map Info), which ensures the capture of geographic information in digital form (Acquisition). Manipulation of data stored in the form of layers (analysis) and management database (archiving), the formatting and visualization and representation in 2D or 3D (Display). Figure 2: Generating a digital elevation model (DEM)

3 Examples of elaboration of photo-interpretations in seismic hazard assessment The SRTM data and digital terrain models (DEM) are used as a cartographic support in the analysis of seismic hazard. The use of the imagery in the pre-seismic phase of assessment directs effectively the field investigations. The analysis of the photo-interpretation is for the establishment: The photo-geological map based on the interpretation of morphostructural with geology units, for detection of tectonic structures in the survey zone. It is produced by using stereographic pairs of aerial photographs (Fig. 3). Scale: Figure 3: An example of the aerial photograph of Arbal area (NW part of Algeria) which reveals: NE-SWE morphotectonic escarpment supposed active fault affecting the Neogene. 2- NNE-SSW, NE-SW (N020-N060), ENE-WSW/E-W (N075 to N090) and NW-SE Ante-Neogene field. The seismotectonic map whose purpose is the allocation of a maximum magnitude likely designated by MCE (maximum credible earthquake) for each seismogenic source identified critical (fault capable of generating an earthquake) in the survey area.

4 Fi gure 4: Historical seismicity of the Eastern Algeria: seismicity data superposed the raster elevation data [Latitudes: N and Longitudes: E] Location of the Low Ech Chellif Valley [Western Algeria] (area under square) Figure 5: Maps of historical seismicity and seismic sources of Low Ech Chellif area (using the SRTM data)

5 Figure 6: Seismotectonic map of the Eastern Algeria [Latitudes: N and Longitudes: E] Also, the use of high resolution satellite images in the post seismic phase opens up new perspectives. Different approaches to developing automated methods of recognizing damage can be developed for buildings and infrastructures in earthquake engineering and disaster management. Conclusion The analysis of spatial data and digital terrain models (DEM) can exceed the overall geological characterization mode. Remote sensing opens the way for validation of knowledge unobtainable by traditional methods. Its use is indisputable in the detection and mapping in the field of seismic hazard. Also, it is a means for information of estimating the damages on the seismic risk management.

6 Reference Bennouar (1994). Materials for the investigation of the seismicity of Algeria and adjacent regions during the twentieth century. Annali di geofisca. Bezeghroud & al,. (1994). Seismicity of Algeria between 1365 and 1989: map of maximum observed intensities. Boughacha (2005). Analyse de la sismicité de l Algérie application à l établissement des cartes des i.m.o et δcff. Thèse de Doctorat d Etat en Sciences physiques Spécialité Géophysique CGS (1995). Le séisme du 18 août 1994 de Beni Chougrane. CGS (1999). Etude de l aléa et microzonage sismiques de la région de Mascara. CRAAG (1994). Les séismes de l Algérie de 1365 à Publication de centre national de Recherche en Astronomie, Astrophysique et Géophysique. SRTM Wordwide Elevation Data [ fails] THOMAS G. (1985). Géodynamique d'un bassin intramontagneux. Le bassin du bas Chelif occidental (Algérie) durant le Mio-Plio-Quaternaire. Thèse d'etat. Uni. Pau. 594p. International Seismological Centre (ISC). 2007, On-Line Bulletin, http// intrenat. Seis.Cent., Thatcham, Unieted Kingdan. U.S Department of the interior/u.s. Geollogical http/// Survey. 2007, On-line Bulletin,