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merce must be maintained. The acts of regulating land use and siting facilities based on potential hazard or the consequences of their failure go right to the heart of how a community functions. Hazard considerations are but a part - often ignored - of the overall decision process. Much remains to be learned about effectively integrating land use strategies into economic development, but experience from many communities shows that even simple restrictions on the use of flood plains, as mentioned above, can reduce the con- sequences of flooding. Controlling building practices offers one of the most effective approaches to limiting the effects of natural hazards. When a structure is designed, constructed, and maintained to resist a hazard, then the hazard has little or no impact. But the design of a structure to withstand a hazardous event is not a simple matter. What forces will the structure encounter, How will its different ele- ments interact' How will the construction mate- rials perform, These are questions the engineer must answer. Many empirical rules have evolved to aid the engineer in constructing buildings that perform well during natural hazards. However, building practices throughout the world are developing rapidly, creating both new dangers and new. opportunities. Some improved construction tech- niques have already proved their worth. For example, using cement mortar rather than lime! sand mortar, using reinforcing steel, and attach- ing diaphragms to walls can reduce the vul- nerability of masonry buildings from almost certain collapse in an earthquake to one of modest or light damage. Similarly, attaching the roof to the walls and the walls to the foundation of a wood frame house can greatly reduce wind de- struction during hurricanes, cyclones, and tor- nadoes. But rapid change in construction practices also poses new dangers. Techniques are often applied far from where they were developed, without regard to their limitations. Further, their perform- ance may be conjectural, not understood from actual experience. Only observations of actual performance in the field - combined with labora- tory research - can validate new methods. Such investigations do not yield results easily or quickly. Among the principal tools for safe construction Like dol/houses slumped ill salld, these reill{orced concrete apartment buildillgs in Niigata, Japan, tilted precipitously, but remailled illtact ill JUlie 1964 whel1 a magnitude 7.5 earthquake "liquefied" the soil bel1eath them, causillg them to subSIde. Durillg strong groulld shakillg, areas with salldy soils alld a high water table call temporarily lose strength alld behave like fluids, a phenomenon known as liquefaction. 23 ~ ~ z ~ " o I ~ " ~ o ~ "