Determination of the major axis direction and macroseismic epicenter of the assessed intensity map based on relocated aftershock sequences

The rapid assessment of an intensity map following a strong earthquake forms the foundation for risk and emergency response in Chinese mainland. determination major axis direction assessed depends on various factors, including nearby active faults, instrumental intensities, distribution aftershocks. To evaluate effectiveness promptly determining based early aftershock distribution, we relocated analyzed sequences occurring within 2 h eighteen aftershock-rich earthquakes with magnitude M s ≥ 6.0 mainland from 2012 to 2021. HypoDD was used relocation, standard deviational ellipse fitting technique employed analysis. Comparing ellipses resulting our analysis macroseismic maps obtained field surveys reveals high level agreement, average difference approximately 9° directions meizoseismal zones. For majority earthquakes, regardless focal mechanisms, lengths axes closely correspond VIII scale. Additionally, spatial aftershocks aids distinguishing seismogenic fault two planes distinctly different dips as indicated by mechanism solution. Moreover, distance between center epicenter systematically increases dip decreases. These findings hold significant scientific value they contribute prompt provide effective guidance response.