3.1.1. Stress change before the 2022 Menyuan earthquake
In this section the ΔCFS was calculated at a 10-km depth (close to the hypocenter depth for the 2022 Menyuan earthquake suggested by USGS) with receiver faults identical to the focal mechanism (strike = 104°, dip = 88°, rake = 15°) of the 2022 Menyuan earthquake (USGSa) induced by 11 historical earthquakes.
Figures 2(a)–2(k) presents the ΔCFS map at a 10-km depth before 2022 individually induced by 11 large earthquakes (Nos. 1–11). Figures 3(a)–3(k) presents the ΔCFS along the Qilian-Haiyuan fault system at a 10-km depth before 2022 individually induced by 11 large earthquakes (Nos. 1–11). All the 11 historical earthquakes increased stress before 2022 in the 2022 Menyuan earthquake rupture zone (segment GH in Figure 3) except for three of them (the 1963 Mw 7.0 Alake Lake earthquake [No. 5], 1986 Mw 6.0 Menyuan earthquake [No. 8], and the 1927 Gulang Mw 8.3 earthquake [No. 11]). The ΔCFS on the 2022 Menyuan earthquake hypocenter before 2022 was changed by -2.886 kPa, 0.208 kPa, 3.957 kPa, and -18.44 kPa by the 1986 Mw 6.0 Menyuan (No. 8), 2016 Mw 5.9 Menyuan (No. 9), 1920 Mw 8.5 Haiyuan (No. 10), and 1927 Mw 8.3 Gulang (No. 11) earthquakes, respectively (Figures 2 and 3). The stress change on the 2022 Menyuan earthquake hypocenter by the other seven earthquakes (Nos. 1–7) was negligible owing to the limited ΔCFS values (between -0.01 kPa and 0.02 kPa) (Figures 2 and 3).