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Published June 1994 | Published
Journal Article Open

Foreshocks, Aftershocks, and Earthquake Probabilities: Accounting for the Landers Earthquake


The equation to determine the probability that an earthquake occurring near a major fault will be a foreshock to a mainshock on that fault is modified to include the case of aftershocks to a previous earthquake occurring near the fault. The addition of aftershocks to the background seismicity makes its less probable that an earthquake will be a foreshock, because nonforeshocks have become more common. As the aftershocks decay with time, the probability that an earthquake will be a foreshock increases. However, fault interactions between the first mainshock and the major fault can increase the long-term probability of a characteristic earthquake on that fault, which will, in turn, increase the probability that an event is a foreshock, compensating for the decrease caused by the aftershocks.

Additional Information

© 1994, by the Seismological Society of America. Manuscript received 2 August 1993. I would like to thank Andy Michael, Egill Hauksson, Jim Savage, and especially Tom Heaton for careful and thoughtful reviews of this article.

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August 20, 2023
August 20, 2023