Figure 3: ΔCFS along the Qilian-Haiyuan fault system at a 10-km depth before 2022 induced by: (a) the 1932 Mw 7.5 Changma earthquake (No. 1), (b) the 1954 Mw 7.3 Shandan earthquake (No. 2), (c) the 1954 Mw 7.0 Minqin earthquake (No. 3), (d) the 1937 Tuosuo Lake earthquake (No. 4), (e) the 1963 Alake Lake earthquake (No. 5), (f) the 1990 Mw 7.0 Gonghe earthquake (No. 6), (g) the 1990 Mw 6.2 Tianzhu earthquake (No. 7), (h) the 1986 Mw 6.0 Menyuan earthquake (No. 8), (i) the 2016 Mw 5.9 Menyuan earthquake (No. 9), (j) the 1920 Mw 8.5 Haiyuan earthquake (No. 10), and (k) 1927 Mw 7.9–8.3 Gulang earthquake (No. 11); (l) ΔCFS along the Qilian-Haiyuan fault system at a 10-km depth just after 2022 based on the 2022 Mw 6.6 Menyuan earthquake (No. 12). The red dashed line indicates the 2022 earthquake rupture (segment GH) on the Qilian-Haiyuan fault system (segment BC). The longitude of the 2022 Menyuan earthquake epicenter is marked with a black star. Segments AD, DE, EF, and FB indicate the LLLF, JQHF, MMSF, and LHSF, respectively, in the Tianzhu Seismic Gap (segment AB).
Figure 4 (a) presents the cumulative ΔCFS map at a 10-km depth before 2022 induced by 11 large historical earthquakes (Nos. 1–11). Figure 5 (a) illustrates the cumulative ΔCFS distribution along the Qilian-Haiyuan fault system resulting from these 11 earthquakes. The stress before 2022 was unloaded in the 2022 Menyuan earthquake rupture zone (segment GH in Figures 4 (a) and 5). An ΔCFS decrease of about -15.38 kPa was observed at the 2022 Menyuan earthquake hypocenter. This unloaded stress was mainly controlled by the 1927 Mw 8.3 Gulang earthquake (-18.44 kPa) (No. 11) by comparing Figure 5 (a) with Figure 3.