In recent years disaster risk has been defined, for management purposes, as the potential economic, social and environmental consequences of hazardous events that may occur in a given period of time. However, in many cases, the concept of risk has been defined in a fragmentary way according to each scientific discipline involved in its estimation. In order to evaluate risk according to the above stated definition, a multidisciplinary evaluation is necessary. This evaluation should take into account not only the expected physical damage, the number and type of casualties or economic losses, but also the conditions related to social fragility and lack of resilience which favour the second order effects when a hazardous event strikes an urban centre.