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Long aftershock sequences within continents and implications for earthquake hazard assessment


One of the most powerful features of plate tectonics is that the known plate motions give insight into both the locations and average recurrence interval of future large earthquakes on plate boundaries. Plate tectonics gives no insight, however, into where and when earthquakes will occur within plates, because the interiors of ideal plates should not deform. As a result, within plate interiors, assessments of earthquake hazards rely heavily on the assumption that the locations of small earthquakes shown by the short historical record reflect continuing deformation that will cause future large earthquakes1. Here, however, we show that many of these recent earthquakes are probably aftershocks of large earthquakes that occurred hundreds of years ago. We present a simple model predicting that the length of aftershock sequences varies inversely with the rate at which faults are loaded. Aftershock sequences within the slowly deforming continents are predicted to be significantly longer than the decade typically observed at rapidly loaded plate boundaries. These predictions are in accord with observations. So the common practice of treating continental earthquakes as steady-state seismicity overestimates the hazard in presently active areas and underestimates it elsewhere.

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Figure 1: Aftershock sequences following large earthquakes in different tectonic settings.
Figure 2: Aftershock durations and fault loading rates for selected large earthquakes in different tectonic settings.


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We thank Y. Yang for assistance in preparing the figures and Supplementary Information, and H. Wang for providing the Chinese earthquake catalogue. M.L.’s research is supported by NSF/OISE grant 0730154 and a grant from the Chinese Academy of Sciences. We also thank E. Calais, A. Friedrich, R. Smith and R. Stein for discussions, and T. Parsons and Y. Kagan for reviews.

Author Contributions S.S. developed the friction-based model and much of the data set. M.L. developed the Chinese data and the viscous relaxation model. Both authors discussed the results and participated in the writing.

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Correspondence to Seth Stein.

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Stein, S., Liu, M. Long aftershock sequences within continents and implications for earthquake hazard assessment. Nature 462, 87–89 (2009).

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