Identifying , Understanding , and Analyzing

T he notion that our nation’s critical infrastructures are highly interconnected and mutually dependent in complex ways, both physically and through a host of information and communications technologies (so-called “cyberbased systems”), is more than an abstract, theoretical concept. As shown by the 1998 failure of the Galaxy 4 telecommunications satellite, the prolonged power crisis in California, and many other recent infrastructure disruptions, what happens to one infrastructure can directly and indirectly affect other infrastructures, impact large geographic regions, and send ripples throughout the national and global economy. In the case of the Galaxy 4 failure, the loss of a single telecommunications satellite led to an outage of nearly 90% of all pagers nationwide [1]. From an interdependency perspective, it also disrupted a variety of banking and financial services, such as credit card purchases and automated teller machine transactions, and threatened key segments of the vital human services network by disrupting communications with doctors and emergency workers. In California, electric power disruptions in early 2001 affected oil and natural gas production, refinery operations, pipeline transport of gasoline and jet fuel within California and to its neighboring states, and the movement of water from northern to central and southern regions of the state for crop irrigation [2]-[6]. The disruptions also idled key industries, led to billions of dollars of lost productivity, and stressed the entire Western power grid, causing far-reaching security and reliability concerns [7]-[10].