Unreinforced Masonry Buildings
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UNCERTAINTY Philipp Schmidt-Thomé Geological Survey of Finland (GTK), Espoo, Finland
Synonyms Incertitude; Insecurity Definition Uncertainty encompasses all factors of the lack of knowledge towards the exact probability, the timing, magnitude and potential frequency of return of a natural hazard event. Discussion Uncertainty extends to the imprecise knowledge of the risk, that is, the precise knowledge of vulnerabilities at any given time of a hazardous event. Uncertainty comprises all unknown inaccuracies. The term is not unanimously defined but it certainly comprises a larger concept than error, the statistical expression for known inaccuracies. Natural hazards are complex phenomena that cannot be forecasted precisely. Allegedly one of the most descriptive manners to describe the risk types attached to natural hazards, including uncertainty aspects, was developed by the German Advisory Council on Global Change – WBGU (2000). WBGU risk types are based on prominent figures from the Greek mythology, and most natural hazards fall into the “cyclope” type risks. Cyclopes are mighty giants with only one eye, meaning that the extent of damage is well known but that the perspective is lost, that is, the probability (or timing) of occurrence. Beyond this, uncertainty is a concept that includes imperfect knowledge, inaccuracy, lack of reliability and inconsistency, and so on of the data (Pang, 2008). Uncertainty is mainly grouped into two types: (1) Aleatory (external) uncertainty is the unpredictability and
randomness of the precise moment of an event or process (rock fall, climate change), and (2) Epistemic (internal) uncertainty is the inaccuracy of data and the shortcomings in the understanding of complex processes (models). According to this distinction epistemic uncertainty can be encountered by improving data sets and models. Aleatory uncertainty is subject to probability analysis (e.g., return periods) and epistemic uncertainty is encountered by expert knowledge. The complexity of uncertainty plays a vital role in the design and estimation of mitigation and adaptation efforts. The cost-benefit analysis of measures to minimize risks related to natural hazards, or the potential impacts of climate change, is greatly dependent on data accuracy. The higher the uncertainty the higher is the potential to invest in inappropriate measures or to take unsustainable decisions. There are several approaches to visualize uncertainty in hazards to better inform about the complexity of the problem and ultimately to support decision making (Pang, 2008). The integration of uncertainty in hazard maps has direct effects on, and may be used to support, the delineation of hazard zones (zoning (further reading: Bostrom et al., 2008), Hoffmann & Hammonds, 1994). Traditionally hazard maps have sharp borders between for instance, “high” and “medium” hazard areas. Since natural events seldom follow strict borders introduced by human concepts, the introduction of uncertainty concepts into hazard maps assists the perception of the potential sp
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