Isoseismal line of Sichuan Changning M_S6.0 earthquake in 2019 based on precisely located aftershocks sequence

The double-difference location method was utilized to determine the locations of the main shock of Changning M_S6.0 earthquake in Sichuan Province and its aftershocks within 24 hours. A magnitude-weighted direction distribution fitting for the relocated aftershocks results in the major axis and the center of aftershock area. A comparison with the major axis and geometric center of the isoseismal line of intensity Ⅶ shows that the directions of major axis between the aftershock area and the Ⅶ intensity area are close to each other （with a difference of 4°）, and the length of the two axes are approximately equal （with a difference of 4 km）. Furthermore, the centers of the aftershock area and isoseismal line both locate northwest of the relocated main shock, and the isoseismal center deviates towards the hanging wall from the center of the aftershock area with a distance of about 3.0 km. The isoseismal map of Changning M_S6.0 earthquake shows visible hanging wall/footwall effects, i.e., the high-intensity area of the hanging wall is almost 2.1 times larger than that of the footwall, and the isoseismal center shifts towards the hanging wall. The fitting result of the aftershocks within 2 hours is consistent with that of 24 hours, and the comparison with isoseismal map results in the same conclusion. The results of this research might provide a new idea for the revision of the pre-assessment intensity map for shallow-source moderate-strong earthquakes.