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Constraints on the size of the smallest triggering earthquake from the epidemic-type aftershock sequence model, Båth's law, and observed aftershock sequences
Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
Laboratoire de Physique de la Matière Condensée, UMR 6622, CNRS, Université de Nice Sophia-Antipolis, Nice, France
Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California, USA
The physics of earthquake triggering together with simple assumptions of self-similarity imply the existence of a minimum magnitude m 0 below which earthquakes do not trigger other earthquakes. Noting that the magnitude m d of completeness of a seismic catalog is not, in general, the same as the magnitude m 0 of the smallest triggering earthquake, we compare observed aftershock sequence parameters with the predictions made by the epidemic-type aftershock sequence model to constrain the value of m 0. In particular, we use quantitative fits to observed aftershock sequences from three previous studies, as well as Båth's law, to obtain four estimates of m 0. We show that the branching ratio n (average number of triggered earthquakes per earthquake, also equal to the fraction of aftershocks in a seismic catalog) is the key parameter controlling the estimate of the minimum triggering magnitude m 0. Conversely, physical upper bounds for m 0 estimated from rate and state friction indicate that at the very least, 55% of all earthquakes are aftershocks.
Received 11 November 2004; accepted 22 April 2005; published 6 August 2005.
Citation: (2005), Constraints on the size of the smallest triggering earthquake from the epidemic-type aftershock sequence model, Båth's law, and observed aftershock sequences, J. Geophys. Res., 110, B08304, doi:10.1029/2004JB003535.
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