ABSTRACT

This paper presents GIS-based deterministic approaches for earthquake-induced landslide hazard evaluation and zonation. These approaches combine numerical slope stability analysis with GIS spatial analysis to evaluate earthquake-included slope failures, both shallow and deep-seated. The study focuses on GIS-based procedure of landslide hazard zonation, which involves one-, two-, and three-dimensional deterministic methods. The conventional slope stability analysis methods such as the widely used limit equilibrium methods in geotechnical engineering including block sliding model, methods of slices, and Hovland's column method were incorporated into the GIS- based procedure.

This paper also discussed causative factors analysis of earthquake-included landslide hazards including the determination of peak ground acceleration, evaluation of the topographic effect of ground motion, and the seismic response analyses. The developed approach was applied to a specific site in the Balsamo Ridge area next to the city of Nueva San Salvador, E1 Salvador. The study demonstrated that the zonation map produced using the 2D and 3D methods has achieved such a level of accuracy that can be used for engineering design and decision-making in land use development.

1 INTRODUCTION

Zonation refers to the division of the land surface into areas and the ranking of these areas according to the degree of actual or potential hazard from landslides or other mass movements on slopes (Varnes, 1984). The goal of earthquake-induced landslide susceptibility zones where landslides could be induced by future strong earthquake shaking.

Although earthquakes can hardly be predicted, the susceptibility to earthquake-induced landslides of area can be assessed on the basis of potential ground motion, geological, and geomorphologic conditions.

During last two decades, research has proven that GIS (Geographic Information Systems) provides a powerful tool for landslide hazard zonation. However, seismic- induced landslide susceptibility assessment inherits complex uncertainties of terrain, seismic, and geotechnical parameters. For deterministic analysis models such as the infinite slope model is only applicable for shallow slope sliding prediction. In fact, circular slope failure and deep slope sliding occur more commonly than otherwise in earthquake prone areas and these types of landslides usually are the major cause of property damage and fatalities. It is essential to develop a reliable analysis model that considers failure modes, geotechnical parameters, and uncertainties to achieve the accuracy needed for seismic-included landslide hazard evaluation and zonation.

This paper presents a newly developed GIS-based deterministic approach for earthquake-induced landslide hazard evaluation and zonation. This approach combines numerical slope stability analysis with GIS spatial analysis to evaluate earthquake–induced slopes failures. The scopes of the study focused on the GIS-based procedure of landslide hazard zonation, the evaluation of peak ground acceleration, and the topographic effect of ground motion. The widely used limit equilibrium methods in geotechnical engineering including one-dimensional (1D) block sliding model, two-dimensional (2D) methods of slices, and three- dimensional (3D) Hovland's column methods were in corporate into this GIS-based procedure.

The slope stability was calculated using customized programs combine VBA (Visual Basic for Applications) with GIS grid- based spatial analysis.

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