As the human population of our planet rises to hitherto unprecedented levels, we find ourselves wondering whether the half-century from 1990 to 2040 might be remembered not so much as the age when the oil ran out, as the age of construction. Never before have we built so many dwellings, roads, dams, and civic structures than will be constructed during the span of this half-century. A little reflection suggests that in our (allegedly) highly evolved society, with our sophisticated knowledge of the forces of nature and the strengths of materials, we would be stupid to commit the unforgivable sin of knowingly constructing buildings that will crush and maim our descendants. Yet in many parts of the world this is indeed what we are doing. Homo sapiens decided long ago to live in houses. Other animals do it, but rarely do they build such precarious structures as do humans. The nests of birds are woven to be resilient, mammals and reptiles live in caves selected for their permanence, burrows are dug by animals content with the knowledge that a little more burrowing is all that’s needed to keep the walls in place, or the driveway clear. Only humans spend at least eight hours of every turn of the planet within a dwelling assembled from a variety of materials that are often close to the point of structural failure, and often without considering the consequences of constructing permanent dwellings in regions subject to geologically extreme events. The shift from Homo the hunter-gatherer to Homo urbanensis means that many of the remaining 16 hours of each day are spent in another structure, more often than not also assembled with an eye on thrift —maximum volume for minimum cost. Even the journey to and from these different structures can expose humans to seismic risks—as is evident from the collapse of bridges and overpasses in recent earthquakes. The damage done by an earthquake is caused by shaking, either directly or indirectly (via landslides, etc.). Shaking involves accelerations: the rate at which speed changes or, in qualitative terms, what can be thought of as “jerkiness.”
