ABSTRACT
Since the first major and most recent Brazilian geological disasters triggered in 2011 in the state of Rio de Janeiro, the Geological Survey of Brazil (CPRM) has started a geological and geotechnical mapping of High and Very High risk areas in targeted municipalities, on an emergency basis, by demand of the Federal Government. These areas were not only chosen by their susceptibility to geological processes, such as landslides, or by their susceptibility to hydro-meteorological phenomena, such as inundations and floods, but especially due to their historical record of different types of damage and losses, including life losses. This national mapping was due in 2015, ending a 5-year cycle of continuous effort to help mitigate and reduce risks. During the process, the most populous area of the country, the Metropolitan Area of São Paulo (MASP), was intensely studied by the CPRM and by several other research institutes in matters of geological risk. This region has an area of about 7,946.96 sq. km, comprising 39 densely urbanized municipalities, with a population of more than 20 million people living mostly on rough terrain, on geological units highly susceptible to mass movement. The fragile human occupation, living in precarious and substandard housing complexes, is also mostly located in steep terrains, putting its most vulnerable population at high risk, especially when the slopes suffer modifications without proper engineering measures, urban planning or removal of high risk buildings. 27 municipalities have been subject to these studies, which were conducted not only by the CPRM, but also by other state research institutes throughout the years. There is also the case of the city of São Paulo itself, which recently have been the target of a large scale geological risk mapping. In examining and assessing the available technical studies so far, it is easy to see that risk areas and sectors highlighted in different sources, using similar methodologies, have certain aspects in common, alongside physical conditions and predisposing factors that form, in fact, constraints to human use and occupation. The identifiable pattern is the typical human-made scenario of precarious settlements on susceptible geological formations, ordinarily triggering landslides mainly in cut and fill slopes. Even where the terrain susceptibility is not high, the main risks in the MASP are being triggered by human activity on precarious settlements. Apart from the current work, there is also information from local civil defence and protection units on landslide occurrences, plus field surveys by researchers’ teams pointing towards this pattern of human-induced geological risk.
