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Aftershock Zone Scaling

Yan Y. Kagan

Published March 2002, SCEC Contribution #603

We investigate the distribution of aftershock zones for large earthquakes (scalar seismic moment M >= 10^19.5 Nm, moment magnitude, m >= 7). Mainshocks are selected from the Harvard CMT catalog and aftershocks from the PDE (NEIC) catalog. The aftershock epicenter maps are approximated by a two-dimensional
Gaussian distribution, the major ellipse axis is taken as a quantitative measure of the mainshock focal zone size. The dependence of zone length, l, on earthquake size is studied for three representative focal mechanisms: thrust, normal, and strike-slip. Although the numbers of mainshocks available for
analysis are limited (maximum a few tens of events in each case), all earthquakes show the same scaling (M propto l^3). There is no observable scaling break or saturation for the largest earthquakes (M >= 10^21 Nm, m >= 8). Therefore, our study suggests that earthquake geometrical focal zone parameters are self-similar.

Kagan, Y. Y. (2002). Aftershock Zone Scaling. Bulletin of the Seismological Society of America, 92(2), 641-655. doi: 10.1785/0120010172.