Can the time, location, and magnitude of future earthquakes be predicted reliably and accurately? In their Perspective, Geller et al .'s answer is “no.” Citing recent results from the physics of nonlinear systems “chaos theory,” they argue that any small earthquake has some chance of cascading into a large event. According to research cited by the authors, whether or not this happens depends on unmeasurably fine details of conditions in Earth's interior. Earthquakes are therefore inherently unpredictable. Geller et al . suggest that controversy over prediction lingers because prediction claims are not stated as objectively testable scientific hypotheses, and due to overly optimistic reports in the mass media.

SUMMARY Earthquake prediction research has been conducted for over 100 years with no obvious successes. Claims of breakthroughs have failed to withstand scrutiny. Extensive searches have failed to find reliable precursors. Theoretical work suggests that faulting is a non‐linear process which is highly sensitive to unmeasurably fine details of the state of the Earth in a large volume, not just in the immediate vicinity of the hypocentre. Any small earthquake thus has some probability of cascading into a large event. Reliable issuing of alarms of imminent large earthquakes appears to be effectively impossible.

We study four ML ‐ 2.7 earthquakes on the San Andreas Fault in Central California. The first two events occurred within five minutes of each other in November 1978; the two events in January 1979 occurred within a nine hour period. The CALNET (USGS local array) seismograms of these four events display only some general similarity. However, when low ‐ pass filtered below 5 Hz, the four events have nearly identical seismograms. The similarity is even more striking in the pass‐band below 2 Hz. This suggests that all four events are within a radius of no more than a quarter wavelength, or about 200 ‐ 400 m. Although no definitive conclusion can be reached from a study of only four earthquakes, our results strongly suggest that the following hypothesis should be further tested: Small to moderate earthquakes may commonly be much more tightly clustered in both hypocentral location and depth than is suggested by routine locations from local arrays. The physical basis of this clustering is that the earthquakes represent repeated stress release at the same asperity, or stress concentration, along the fault surface. Identification of such asperities might be useful in understanding the sequence of events leading to the initiation of a larger earthquake.

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