Tsunami

Tsunami

Tsunamis are gravitational waves generated in the ocean when a detonating phenomenon displaces a large body of water vertically. These waves can travel great distances and impact the coasts of several continents. There are different types of tsunamis which differ mainly in the triggering mechanism that induce them. In this project, only those associated with earth crust tectonic processes, commonly known as tectonic tsunamis, were considered. 

The tsunami hazard model is based on a global model which considers the occurrence rate of earthquakes in major submarine seismic sources. Hazard scenarios for all tsunami-prone regions in the world were defined. The hazard is presented in terms of a set of scenarios, where each one of these is characterized by an annual frequency of occurrence and the intensities are defined in terms of two parameters: the expected value and the standard deviation.

Vulnerability

The vulnerability of infrastructure components is defined using mathematical functions that relate the intensity to the direct physical impact. Such functions are called vulnerability functions and they must be estimated and assigned for each one of the components identified, and for each hazard considered. Vulnerability functions provide the variation of the probability moments of the relative loss with increasing intensity (see Figure below).

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Vulnerability functions allow the transformation from the occurrence of a hazard event and the local intensities caused by it, to  quantification of direct losses on the exposed elements

Risk

The proposed fully probabilistic risk assessment considers multiple events of multiple hazards, which implies the simulation of thousands of possibilities in which those hazards may manifest, under future changing climates. For each simulated event, the damage to the infrastructure system is quantified through the vulnerability functions. Repeating this process for different hazard events results in different damages simulated for the same infrastructure, each rendering some economic loss with a probability of occurrence. Typically, low damage events have a higher probability of occurrence, which means they are more frequent, and high damage events have lower probabilities or are less frequent (see Figure below). This collection of loss amounts and probabilities makes up a truly probabilistic and multi-hazard risk assessment of any infrastructure system. This process will be applied to all infrastructure sectors country-by-country

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Although disaster risk is fully quantified by the set of losses, it is more practical to express it as condensed metrics that summarize the results into curves or point estimates. Two of the most widely used metrics are the Probable Maximum Loss (PML) curve and the Average Annual Loss (AAL). 

The PML curve describes the variation of losses to the return period. It fully integrates all the consequences, even of different hazards, to define the feasibility that large loss amounts occur sometime in the future. 

On the other hand, the AAL is a multi-annual loss average, like an insurance premium, i.e., it quantifies an annual loss that, in the long term, accumulates to the total amount of losses that will be caused by disasters to the infrastructure. It is a multi-hazard metric as well.