Earthshaking Science: What We Know (and Don't Know) about Earthquakes

  • Susan Elizabeth Hough
Princeton University Press: 2002. 272 pp. $24.95, £17.95

Seismologists have been grouped, unfavourably, with economists in that they are both great at telling you why an event happens after it has happened. This sentiment reflects frustration with our limited knowledge of earthquake behaviour. Why don't we understand earthquakes better? And why can't we predict them?

Large earthquakes occur infrequently, and the processes that are the key to understanding them are removed from our sight by miles of opaque material. Moreover, the sudden rupture of a fault in an earthquake is a nonlinear process that occurs within materials that vary strongly in their properties and appear to be complex at all spatial scales. Given these challenges, perhaps it is not surprising that we lack a comprehensive understanding of earthquake behaviour.

A more optimistic view of our limited understanding is that the science of earthquakes is not mature. Almost every new well-recorded earthquake seems to have at least some surprising aspect. We are still on the steep part of the learning curve.

Earthshaking Science takes on the difficult task of reviewing the state of earthquake science at a time when the field is evolving rapidly. Its author, Susan Hough, has done an admirable job of clearly and accurately illuminating the boundary between our knowledge and our ignorance. In the process, she outlines some of the major outstanding problems in the field and provides a balanced and insightful view of them from several sides. Time and again as I read this book I thought to myself that she had advocated a particular position too strongly, only to find on the following page that she would offer an equally strong counterargument.

Hough, who has experience of both earthquake research and public outreach, has written a book that is accessible to readers in other disciplines and to a non-technical audience, but provides enough thoughtful commentary and perspectives to hold the attention of specialists.

An important part of any general book on earthquakes is how it treats short-term earthquake prediction — a topic that is central to seismology and foremost in the minds of non-seismologists. In this book there is not a great deal of material on earthquake prediction, which might disappoint readers outside the field. This de-emphasis is not surprising, though, given the lack of success to date. Instead, the discussion focuses on whether or not earthquakes are predictable even in theory (see Nature web debate; http://www.nature.com/nature/debates). As elsewhere, Hough delivers an even-handed and up-to-date treatment of both sides of the issue.

The book excels in its treatment of the prediction of potentially damaging strong ground motion in the near field of an earthquake. The ability to predict strong ground motion is arguably more important than the ability to predict earthquakes. Seismologists use ground-motion prediction in the form of probabilistic seismic hazard analysis (PSHA) to characterize earthquake risk.

PSHA, as used in building codes, for example, is an estimate of the distribution of ground motion with a 10% probability of being exceeded over a 50-year time interval. A lot goes into this estimate, and this book explains it clearly. To my knowledge there is no other accessible treatment of this topic. The test that precariously balanced rocks offer of the validity of PSHA is a nice example of the currency of the material in this book.

Earthshaking Science is not a textbook or a coffee-table book. But it is a readable tour of many key aspects of earthquake science. The author focuses on California but also covers the poorly understood earthquakes in the central and eastern United States. What's missing is a thorough treatment of the many earthquakes in other tectonic environments. One can hardly fault the author for this, because it would require a considerably larger book. Moreover, much of the research knowledge needed to write such a book at the same level does not yet exist. But it soon will.

Recently deployed modern seismic and geodetic monitoring networks in Japan, as well as parallel efforts being contemplated in the United States, have led to the discovery of new phenomena. In the past year, discoveries of large aseismic transients and what appears to be an entirely new type of seismic event deep under Japan are changing our views of fundamental earthquake processes. It is my strong expectation that the author will have a lot of new material to incorporate into the second edition.

More on earthquakes

The Mechanics of Earthquakes and Faulting, 2nd edn by Christopher H. Scholz Cambridge University Press, $130, £90 (hbk); $48, £32.95 (pbk)