The following HTML text is provided to enhance online
readability. Many aspects of typography translate only awkwardly to HTML.
Please use the page image
as the authoritative form to ensure accuracy.
ing rapidly (Figure 1.4) and will face risks similar to those of existing megacities, such as Los Angeles, Istanbul, and Singapore. One expert has speculated that the urbanization in earthquake-prone areas of the developing world may result in a four- to tenfold increase in the annual fatality rate over the next 30 years, reversing a long-standing trend (7).
The losses expected from future events (risk) depend on the population and amount of infrastructure concentrated in a given area (exposure) and the vulnerability of the built environment (fragility), as well as the hazard itself. The seismic hazard levels in Alaska and California are both high, but California’s exposure is much greater, which yields a much larger total risk (Figure 1.3). The growth in losses charted in Figure 1.2 comes primarily from the increased exposure, especially in urbanizing regions (8). Exposure can be lowered by a judicious choice of building sites and careful land-use planning; but only by so much—in seismically active regions, all sites face significant hazard. Earthquake risk reduction must thus rely on lowering vulnerability through earthquake-resilient design of new structures and retrofitting or rehabilitating inadequate older structures to improve their seismic safety. Provisions for earthquake design are now an integral part of building codes in most seismically active parts of the United States, although some states with moderate earthquake risk do not have state seismic codes (see Chapter 2). Code improvements and related problems of implementation continue to require scientific guidance to take into account regional and local variations in seismic hazards, as well as uncertainties and improvements in hazard estimates (9).
The fundamental question of how much to invest in seismic safety has become a pressing problem for the national economy. Several hundred billion dollars are currently spent per annum on new construction in seismically active areas of the United States, and about 1 percent of this overall investment is associated with seismic reinforcement (10). Seismic retrofitting is much more expensive; the costs for unreinforced masonry buildings are typically about 20 percent of new construction, and the values for other building types are comparably high. An alarming example can be found in Los Angeles County, where a recent study showed that more than half of the hospitals are vulnerable to collapse in a strong earthquake. The cost for upgrading these facilities to state-mandated levels of seismic safety has been estimated conservatively at $7 billion to $8 billion, which exceeds the entire assessed value of all hospital property in the county and comes at a time when nearly all hospitals are losing money (11). Resolving such economic and political issues is at least as difficult as the engineering and science issues, and it illustrates the need for coordinated planning across all aspects of seismic safety. To facilitate planning, understandable earthquake information must be made avail-