Debate in 1999

The contributions to the debate about earthquake prediction research in Nature so far, clearly show that we have hardly scratched the surface of the problem of how earthquake ruptures initiate and how to predict them. This arises from the difficulty of the problem and the lack of a vigorous program to study these questions. As Andrew Michael has said, funding for earthquake prediction research is a small fraction of the seismology program, in the U.S., and seismology is poorly funded compared to disciplines like astronomy.

How well can we predict earthquakes? As suggested in Ian Main's introduction to this forum, we can easily predict the behaviour of populations of earthquakes and we clearly cannot completely predict the behaviour of individual earthquakes. But where is the boundary between the easy and the impossible? In search of this boundary let us take a tour through Ian Main's four levels of earthquake prediction.

There has been a recent recrudescence^1,2 of the long debate on the feasibility of short-term earthquake prediction, namely, the prediction, with a lead time of days to weeks, of the time, location and magnitude of a future event. This type of earthquake prediction is inherently difficult to research and has a chequered past, with many intriguing but fragmentary observations of possibly precursory phenomena but no scientifically based and verified successes³.

The recent earthquake in Colombia (Fig. 1) has once again illustrated to the general public the inability of science to predict such natural catastrophes. Despite the significant global effort that has gone into the investigation of the nucleation process of earthquakes, such events still seem to strike suddenly and without obvious warning. Not all natural catastrophes are so apparently unpredictable, however.

Unfortunately, it is typical for debates about earthquake prediction research to be based in part on incorrect assertions^1,2. The first two sentences in the moderator's introduction follow this tradition. Contrary to his suggestion, the recent earthquake in Colombia has done nothing to show the inability or ability of science to predict earthquakes, because this problem simply has not been studied in Colombia.

For the public, the main question that seismologists should ask themselves is, "Can earthquakes be predicted?". Nature's earthquake prediction debate follows this simple line of inquiry, although presented in a slightly more subtle form by Ian Main: "How accurately and reliably can we predict earthquakes, and how far can we go in investigating the degree of predictability that might exist?" This is still, however, a question formulated under social pressure. I argue that this question should be left to one side by scientists to allow progress in a more general and comprehensive framework, by studying the whole set of crustal instabilities — or 'transients' — and not only earthquake precursors.

Because large earthquakes release huge amounts of energy, many researchers have thought that there ought to be some precursory phenomena that could be consistently observed and identified, and used as the basis for making reliable and accurate predictions. Over the past 100 years, and particularly since 1960, great efforts, all unsuccessful, have been made to find such hypothetical precursors. For further details see my review¹, which includes eight pages of references (in 6-point type, to save space) to this vast body of work.