Adobe structures in many highly seismic parts of the world (e.g., eastern Turkey, Iran, Pakistan, Latin America) not only have collapse-prone walls but also very heavy roofs (68,69). When collapsing, these heavy walls and roofs tend to kill many of the people in the homes (70,71). In the United States, unreinforced masonry buildings abound throughout earthquake-prone regions of the central United States (e.g., the New Madrid seismic zone). Most of these unreinforced masonry buildings also remain without any degree of earthquake retrofit for seismic safety.

Concrete-framed houses are generally safer (i.e., less likely to collapse), but they are also vulnerable, and when they do collapse, they are considerably more lethal and kill a higher percentage of their occupants than masonry buildings. In the second half of this century, most of the earthquakes striking urban centers have involved collapses of reinforced concrete buildings, and the proportion of deaths due to the collapse of concrete buildings is significantly greater than earlier in the century (Figure 8-6). Reinforced concrete requires sophisticated construction techniques; however, it is often used in communities around the world where either technical competence is inadequate or inspection and control are lacking. Catastrophic failures of modern reinforced, concrete-slab buildings caused by the collapse of their supports have recently been described in Mexico City (1985), El Salvador (1986), and Armenia (1988) (72-74). Whereas the debris of buildings of adobe, rubble masonry, and brick can be removed with primitive tools, reinforced concrete poses grave problems for rescuers, particularly if not enough special and heavy equipment is available (48).