The 1906 earthquake shook many of San Francisco's buildings down to their foundations (top). But since then the city has nevertheless been building skyward, as seen in 2003 (bottom).

Scientists estimate that nearly 40 percent of the city's buildings could be destroyed in the next big quake. Among the hardest hit may be San Francisco's housing, more than 80 percent of which was built before the introduction of earthquake-proof building codes in 1970.