The goal of these analyses would be to establish significant risk-reduction measures and operational improvements, including techniques for hardening the infrastructure and procedures for training local responders.
It is clear that the critical infrastructure of the United States—defined as the nation’s systems of electric power, telecommunications, gas and oil production, storage and transportation, banking and finance, transportation, water supply, and emergency services—presents significant targets for terrorists, and recent events show that the number and magnitudes of these threats are increasing. Thus modeling U.S. critical infrastructure vulnerabilities—particularly for such objectives as identifying patterns of anomalous behavior, finding weak points in the infrastructure, training personnel, and helping to maintain continuity of operations following terrorist attack—will be of great national importance.
To achieve efficiencies of production, consumption, and reliability, the critical infrastructure’s large distributed systems are organized into networks of interacting elements, as illustrated in Figure 10.4. Interactions might take the form, for example, of material flows (such as oil or commodities) or information flows (such as sensor readings or command-and-control messages). The links are designed and the systems are operated in such a way that decisions based on local incentives and information lead to collective, networkwide benefits.
But the links that promote collective gains also serve as the conduits through which disturbances, whether initiated by nature, human error, or terrorists, are propagated to neighboring systems. As an example, in January 1991 a fiber cable was accidentally cut, blocking 60 percent of long-distance calls in and out of New York City. This single cut also disabled air-traffic-control functions in New York, Washington, D.C., and Boston, which depend on telephone lines for voice and data, and it disrupted operations of the New York Mercantile Exchange and several commodity exchanges (Neumann, 1995).
Fortunately, most system failures—whether triggered by natural or human-made disturbances—are substantially contained in space and time. On occasion, however, disturbances are amplified as they propagate, leading to a catastrophic failure characterized by cascading faults. The major power failure in the Pacific Northwest on August 10, 1996, is one example of cascading faults leading to such a catastrophic failure. Not surprisingly, these rare but catastrophic events are of great interest to terrorists and to those trying to check the terrorists.