it should be emphasized that each of these earthquakes was only moderate to strong in size, less than magnitude-7, and that the impacted areas were limited in size. How well would these communities cope with a magnitude-8 earthquake? What lessons can be drawn from the resilience demonstrated for a moderate earthquake in preparing for a great one?

Perhaps experience in dealing with hurricane disasters would be instructive in this regard. In a typical year, a few destructive hurricanes make landfall in the United States. Most of them cause moderate structural damage, some flooding, limited disruption of services—usually loss of power—and within a few days, activity returns to near normal. However, when Hurricane Katrina struck the New Orleans region in 2005 and caused massive flooding and long-term evacuation of much of the population, the response capabilities were stretched beyond their limits. Few observers would argue that New Orleans, at least in the short term, was a resilient community in the face of that event.

Would an earthquake on the scale of the 1906 event in northern California or the 1857 event in southern California lead to a similar catastrophe? It is likely that an earthquake on the scale of these events in California would indeed lead to a catastrophe similar to hurricane Katrina, but of a significantly different nature. Flooding, of course, would not be the main hazard, but substantial casualties, collapse of structures, fires, and economic disruption could be of great consequence. Similarly, what would happen if there were to be a repeat of the New Madrid earthquakes of 1811-1812, in view of the vulnerability of the many bridges and chemical facilities in the region and the substantial barge traffic on the Mississippi River? Or, consider the impact if an earthquake like the 1886 Charleston tremor struck in other areas in the central or eastern United States, where earthquake-prone, unreinforced masonry structures abound and earthquake preparedness is not a prime concern? The resilience of communities and regions, and the steps—or roadmap—that could be taken to ensure that areas at risk become earthquake resilient, are the subject of this report.

EARTHQUAKE RISK AND HAZARD

Earthquakes proceed as cascades, in which the primary effects of faulting and ground shaking induce secondary effects such as landslides, liquefaction, and tsunami, which in turn set off destructive processes within the built environment such as fires and dam failures (NRC, 2003). The socioeconomic effects of large earthquakes can reverberate for decades.

The seismic hazard for a specified site is a probabilistic forecast of how intense the earthquake effects will be at that site. In contrast, seismic risk is a probabilistic forecast of the damage to society that will be caused by earthquakes, usually measured in terms of casualties and economic losses in a



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