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).

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)

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: 1.40.000

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.

Fi

gure 4: Historical seismicity of the Eastern Algeria: seismicity data superposed the raster elevation data

[Latitudes: 38.00°-35.00° N and Longitudes: 5.00-8.50°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)

Figure 6: Seismotectonic map of the Eastern Algeria

[Latitudes: 38.00°-35.00° N and Longitudes: 5.00-8.50°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.

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