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On Shaky Ground

Mark Zoback

Earthshaking Science: What We Know (and Don't Know) about Earthquakes. Susan Elizabeth Hough. xviii + 238 pp. Princeton University Press, 2002. $24.95.

In Earthshaking Science, Susan Hough, a research scientist at the U.S. Geological Survey, offers a basic primer on a range of topics related to earthquake science and engineering. Her objective is to explain current research and controversies to the lay reader—a formidable task, in which she succeeds admirably: A reader with no background in earth science or seismology can easily absorb the material presented.

Hough begins by describing the history of the theory of plate tectonics and follows with some basic information about earthquakes (how they are located, what magnitude means, and so forth). She then goes on to discuss topics that range from the prediction of ground motion (if an earthquake of expected magnitude occurs on a known fault, what factors affect how strongly the ground will shake at a given site?) to seismic hazard analysis and, predictably enough, what she refers to as "The Holy Grail of Earthquake Prediction."

For obvious reasons, nonexpert readers who live in earthquake-prone areas will be interested in the chapters on ground motions and the mapping of seismic hazard. Those who must accept the inevitability of earthquakes are concerned with the way in which anticipated strong ground shaking is calculated. Hough does a very good job of introducing the various factors that affect such calculations. The chapter on mapping seismic hazard is not as effective, however. Probabilistic earthquake forecasts are now the standard technique for communicating earthquake information to the public, so it is important for readers to understand the methodologies used in such analyses—paleoseismic data, earthquake recurrence models, long-term slip rates, fault segmentation and so on. These subjects are not as thoroughly discussed as they should be. Although Hough attempts at the end of the chapter to enumerate the degree of uncertainty inherent in such estimates, she hasn't explained the basic methodologies sufficiently for readers to fully understand those uncertainties.

The illustrations (black-and-white maps, crude cartoons and line drawings) are disappointing. The quality of the figures in the chapter on ground motions is particularly poor, which is surprising given the excellent information on the subject widely available on the World Wide Web and in other places.

Hough's writing style is easy and engaging, and she makes the subject matter entertaining. Sprinkled throughout the text are sidebars on such topics as the historical rivalry between strong- and weak-motion seismologists (something most readers probably don't need or want to know about) and the pedigree (or, more accurately, the lack thereof) of professional geophysicists. Many of these sidebars offer entertaining insights into the everyday lives of earthquake researchers. As Hough points out, those researchers are a unique breed, fascinated by fundamental scientific questions and driven by a desire to help reduce the devastation earthquakes can wreak.

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