Writing about seismic risk is frustrating: The experts know that big earthquakes are going to happen, but not exactly when and where. The ensuing articles are laced with hypotheticals. There is an airy, foamy quality to these stories; as a writer, you long for solid facts and certainties, and wonder whether any of this stuff makes a difference on the ground, in lives of actual human beings who are at risk. For example, here’s a story I wrote five years ago: The next Big One could strike Tokyo, Istanbul, Tehran, Mexico City, New Delhi, Kathmandu or the two metropolises near California’s San Andreas Fault, Los Angeles and San Francisco. Or it could devastate Dhaka, Jakarta, Karachi, Manila, Cairo, Osaka, Lima or Bogota. The list goes on and on …

For years, earthquake scientists have shouted their warnings about the strong likelihood that a major quake would level an impoverished city and kill hundreds of thousands of people. They have said, for example, that Kathmandu, where masonry structures expand so haphazardly that some eventually cantilever over narrow city streets, is every bit as vulnerable as the surrounding Himalayas are majestic.For years, scientists have talked to me about the very high likelihood of a Kathmandu earthquake. It happened Saturday. The experts called it. But being right hasn’t made them any less horrified and saddened by this disaster. In fact, they sounded dismayed, as if overcome with a sense of powerlessness. Tectonic forces are massive and implacable, and human societies are often poor and fragile. MORE