Fractal dimension and b value of the aftershock sequence of the 2008 M S 8.0 Wenchuan earthquake

Abstract

This study analyzed the seismicity of aftershock events recorded around the earthquake fault area following the 2008 Ms 8.0 Wenchuan earthquake (China). We calculated the fractal dimension (D) and b value of the Gutenberg–Richter law for the aftershocks that occurred within one year of the original earthquake. The results showed that the D values of the earthquake fault ruptures reflected the complexities of the fault structures, and that higher D values were obtained for areas with larger fault slip and larger coseismic ground displacement. The b values for the Wenchuan aftershock sequence were relatively small, which indicated that the larger stress changes occurred in the area of the earthquake faults. Generally, b values are associated with the rupture mechanism of earthquake faults. Here, lower b values were correlated with those regions where thrust ruptures occurred and higher b values were found for those areas with strike-slip ruptures. More importantly, medium- and large-sized aftershocks appeared to occur primarily within areas with small D and b values. A positive correlation between b and D was established from the aftershock sequence, which is described by the relation D = 2b.