Editor's Summary

1 October 2009

Earthquakes find fault

A 20-year seismological record of from the Parkfield area of the San Andreas fault has been used to identify two occasions when long-term changes in fault strength seem to have been induced remotely by large seismic events — the 2004 Sumatra–Andaman and the 1992 Landers earthquakes. In both cases, two changes occurred that are consistent with variations in fault strength: variation in the properties of seismic scatterers with time (reflecting stress-induced migration of fluids) and systematic variation in the characteristics of repeating-earthquake sequences. These findings suggest that the largest earthquakes have a global influence on the strength of the Earth's fault systems. In support of that hypothesis, an unusually large number of M 8 earthquakes occurred in the three years following the 2004 Sumatra–Andaman earthquake.

Letter: Remote triggering of fault-strength changes on the San Andreas fault at Parkfield

Taka'aki Taira, Paul G. Silver, Fenglin Niu & Robert M. Nadeau

doi:10.1038/nature08395

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