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Some Properties of “aftershocks” Some properties of Aftershocks Dave Jackson UCLA Oct 25, 2011

Some Properties of “aftershocks” Some properties of Aftershocks Dave Jackson UCLA Oct 25, 2011 UC BERKELEY. Conclusions. Aftershocks are not clearly defined Whether aftershocks have different magnitude dependence or triggering potential depends upon their definition

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Some Properties of “aftershocks” Some properties of Aftershocks Dave Jackson UCLA Oct 25, 2011

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  1. Some Properties of “aftershocks” Some properties of Aftershocks Dave Jackson UCLA Oct 25, 2011 UC BERKELEY

  2. Conclusions • Aftershocks are not clearly defined • Whether aftershocks have different magnitude dependence or triggering potential depends upon their definition • For most reasonable definition, there is suggestive but weak evidence that triggered earthquakes have different magnitude distributions and triggering potential.

  3. ETAS model of earthquake triggering, from Zhuang et al 2008

  4. Stochastic Declustering

  5. Definitions • Mainshock: largest earthquake in a cluster • Foreshock : An earthquake in a cluster, occuring before the mainshock • Aftershock: An earthquake in a cluster, occuring after the mainshock • Triggered event: An earthquake with a low value of the independence probablityf, independent of its own magnitude • Spontaneous event: An earthquake with a high value of the independence probability

  6. Empirical, So Cal, mt=4.2 plus = triggered, triangle = spontaneous

  7. Synthetic data, same parameters as for empirical study

  8. Synthetic data, triggering of mag 4.2+ by mag 3.7+

  9. Magnitude distributions for spontaneous and triggered quakes, California m4.7+ after 1933

  10. Magnitude distribution after randomizing the independence weightings

  11. Conclusions • Aftershocks are not clearly defined • Whether aftershocks have different magnitude dependence or triggering potential depends upon their definition • For most reasonable definition, there is suggestive but weak evidence that triggered earthquakes have different magnitude distributions and triggering potential. Conclusions depend on clustering model

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