4.1. The delayed 2022 Menyuan earthquake
In order to investigate the relation between the three Menyuan earthquakes: the 1986 (Mw 6.0) (No. 8), 2016 (Mw 5.9) (No. 9), and 2022 Mw 6.6 (No. 12) earthquakes, we demonstrated the stress change on the 2022 Menyuan earthquake rupture induced by the 1986 and 2016 Menyuan earthquakes before 2022. We found that the 1986 earthquake decreased the ΔCFS of -2.886 kPa on the 2022 earthquake hypocenter. However, the 2016 earthquake increased the ΔCFS of 0.208 kPa on the 2022 earthquake hypocenter, which supports the previous proposal by Peng et al. (2022) that the 2022 earthquake was triggered by the 2016 earthquake due to stress loading on the 2022 earthquake rupture.
However, the entire 2022 Menyuan earthquake rupture located in a stress shadow with a negative stress (before 2022) of -15.38 kPa on the 2022 Menyuan earthquake hypocenter by considering the cumulative ΔCFS resulting from 11 historical earthquakes (Nos. 1-11) during the period from 1920 to 2022. Generally, earthquake activity in stress shadow zone is prohibited by unloaded stress from the perspective of earthquake interaction (Mallman and Parsons, 2008). This method has been successfully used to investigate the role of earthquake-induced negative stress on the decreased seismic activities related to the 1857 Fort Tejon and 1906 San Francisco earthquakes in the San Andreas Fault system (Simpson et al., 1988; Harris and Simpson, 1996; Harris, 1998; Freed and Lin, 2001; Mallman and Parsons, 2008) and low seismicity in the Bhutan Himalaya (Gahalaut et al., 2011). Based on this finding, we suggest that the 2022 Menyuan earthquake was delayed because of the unloaded stress on the earthquake rupture resulting from historical earthquakes interactions in northeastern Tibet during the past century. By comparing the stress change on the 2022 Menyuan earthquake hypocenter individually by 11 historical earthquake (Nos 1-11), we found that this stress shadow was mainly controlled by the 1927 Mw 8.3 Gulang earthquake.