Landslides Zonation Hazard: relation between geological structures and landslides occurrence in hilly tropical regions of Brazil

Rodrigo I Cerri,Lucilia C Giordano,Marcelo F Gramani,Fábio A.G.V Reis,José Eduardo Zaine

doi:10.1590/0001-3765201720170224

Abstract

This paper presents a new approach of landslides zonation hazard studies, based on an integrated study of structural data along with geomorphological and external factors, in a hilly regions of Brazil, covered by a tropical humid rain-forest, called Serra do Mar. The Serra do Mar consists of a hilly region along the east coast of Brazil, with high slopes and many geological structures in a gneiss - migmatitic terrain. In contrast to traditional approaches, this method proposes that structural data (foliation, fractures and bedding planes) and its relation with the slope geometry, is important to be consider in the landslide zonation hazard, along with declivity, relative relief, soil and rock properties, land use and vegetation cover and hydrogeological and climate factors. Results show that slopes with high hazard have the same dip direction of geological structures. Landslide zonation hazard using structural data contributes to a better understanding of how these structures, preserved in tropical residual soils, influence on slope stability and generates landslides.

Highlights

The studies of shallow landslides in tropical and subtropical rainforest areas consider precipitation dynamics, geomorphological characteristics with special focus on declivity, soil weathering profile, and type/form of anthropic occupation as the main conditioning factors of these processes
Studies that address the geological structures as factors that contributes to landslides process are scarce, especially in the context of these processes in Brazilian hilly regions
The methodological basis of this paper are the research presented by Anbalagan (1992) and Anbalagan et al (2008), who work with landslide zonation hazard, taking into account the geological structures of the terrain, among other parameters

Summary

Introduction

The studies of shallow landslides in tropical and subtropical rainforest areas consider precipitation dynamics, geomorphological characteristics with special focus on declivity, soil weathering profile, and type/form of anthropic occupation as the main conditioning factors of these processes. Little relevance is given to geological structures as a determining factors for shallow landslides occurrence in these areas, mainly in Brazil In this context, studies that address the geological structures (foliations, fractures, bedding planes, etc.) as factors that contributes to landslides process are scarce, especially in the context of these processes in Brazilian hilly regions. Anbalagan (1992) and Anbalagan et al (2008) present the Landslides Zonation Hazard method, which encompasses several parameters to determine the landslides potential These parameters, including geological structures, are traditional conditioning parameters (declivity, altimetry, rock and soil type, soil thickness, land use and vegetation cover, hydrogeological conditions and annual rainfall index) correlating with slope geometry (slope direction, slope value and altimetry) and the geological structures present in the analyzed terrain

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Discussion

Conclusion