Risk Assessment of Earthquake-Induced Landslides in Urban Zones

At present, natural disasters are having a greater impact on population and infrastructure. Excessive exposure and vulnerability of the elements at risk in urban zones and an increase in frequency and severity of natural and anthropogenic phenomena that trigger disasters are the principal causes. Colombia is located in the northwestern corner of South America; around 35% of the people are located in the Andean region, a complex mountain range that crosses the country from south to north which has significant seismic activity. In these kinds of regions where urban residential areas coincide with mountainous terrains, the risk is higher for people and its infrastructure. Due to various social and economic factors, the city of Medellin has grown rapidly with accelerated and unplanned occupation processes. This has resulted in inadequate practices in urbanization and construction techniques on hillsides. These inadequate practices increase building and infrastructure vulnerability levels. Insufficient investment in preventive measures to reduce the fragility of existing buildings are factors causing greater vulnerability in a city where the built area already reaches around 75 km(2). In this paper, a quantitative risk assessment of earthquake-induced landslides based on physical and probabilistic models through a GIS application is proposed. The study zone is located in the eastern side of the city of Medellin, one of the most disaster-prone areas in the city. The model implemented is able to quantify the risk caused by landslide in an area of the city considering different values of horizontal ground acceleration, and also an analysis of the costs arising from damage to the urban infrastructure under different scenarios and structural conditions. With this kind of cost analysis it is possible to determine the amount of investment required to reduce to an acceptable level of safety the risk of urban infrastructure exposed to a disastrous event.