Introduction

Infrastructure networks can experience both component failures and disruptions. The failure or disruption can be accidental or intentional. These incidents can have both economic and human costs. During large disasters, a large number of critical infrastructures are susceptible to damage and disruption. A disaster is usually referred to as an extreme event if it can disrupt a whole system of interdependent infrastructures such as water supply, transportation, telecommunication, and electric power systems. However, a resilient system has the capacity to adapt to the hazard by resisting or changing in order to reach and maintain an acceptable level of functioning. In most cases, this is determined by the degree to which the social system is capable of organizing itself and its functions, based on the experience and lesson from previous disasters (O'Rourke 2007). During disaster one can identify the following categories of causes: (1) Physical destruction of infrastructure network components, (2) disruption in supporting network infrastructure, and in some cases (3) infrastructure network congestions. Furthermore, most critical infrastructure—for example, telecommunication networks—does not have high degree of redundancy (this will be explained in chapter 4, graphs and networks). Also there are interdependencies between critical infrastructures, and some of them lack acceptable levels of resilience under various conditions. For example, electric outages can cause disruption in transportation systems. Furthermore, depending on how self-healing the interacting systems are, there can be varying degrees of costs involved in restoring appropriate functions and serviceability of each system (Townsend and Moss 2005).

Branscomb (2006) discussed three classes of disasters:

1. • Natural disasters

2. • Man-made disasters

3. • Technogenic disasters resulting from human error and failing infrastructure

Societal hazards include political violence, infectious disease pandemics, industrial and transportation accidents, and fraud catastrophes. A major characteristic of societal hazards is that the community or society tends to be organized to deal with those threats. For example, during the September 11, 2001, terrorist attack and Hurricane Katrina in 2015, the U.S. federal government provided the restoration and recovery.