Aftershock zone scaling

We investigate the distribution of aftershock zones for large earthquakes (scalar seismic moment M greater than or equal to 10(19.5) N m, moment magnitude, m greater than or equal to 7). Mainshocks are selected from the Harvard centroid moment tensor catalog, and aftershocks are selected from the Preliminary Determination of Epicenters (NEIL) 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, 1, 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 proportional to l(3)). No observable scaling break or saturation occurs for the largest earthquakes (M greater than or equal to 10(21) N m, m greater than or equal to 8). Therefore, it seems that earthquake geometrical focal zone parameters are self-similar.