5. Conclusions
To investigate the reason behind the 2022 Menyuan earthquake and the seismic hazards of the Tianzhu Seismic Gap from the perspective of earthquake interaction, we simulated the ΔCFS on the Qilian-Haiyuan fault system by several historical earthquakes in the past century. By demonstrating the spatiotemporal stress variation along the Tianzhu Seismic Gap before and after 2022, we reached the following conclusions:
(1) There is a strong stress contrast among different fault segments in the Tianzhu Seismic Gap, which is mainly controlled by 5 historical earthquakes: the 1920 Mw 8.5 Haiyuan, 1927 Mw 7.3 Gulang, 1990 Mw 6.2 Tianzhu, 2016 Mw 5.9 Menyuan, and 2022 Mw 6.6 Menyuan earthquakes.
(2) The 2022 Mw 6.6 Menyuan earthquake was delayed due to the stress shadow in the earthquake rupture caused by the 1927 Mw 8.3 Gulang earthquake.
(3) The stress shadow also covers the fault segment starting from the east of the 2016 Mw 5.9 earthquake to the middle of the JQHF, which may prohibit the future seismic activity in this fault segment to some extent. By acting as a stress barrier to prevent the whole Tianzhu Seismic Gap being ruptured in one event, it consequently may decrease the possibility of generating a future earthquake of magnitude more than M 7.7 in the Tianzhu Seismic Gap.
(4) The east portion of the Tianzhu Seismic Gap starting from the middle of the JQHF to the east end of the LHSF was also stress loaded due to the 1920 Mw 8.5 Haiyuan and 1927 Mw 8.3 Gulang earthquakes, indicating its increased seismic hazards. More attention should be paid to the future hazards prevention in the east portion of the Tianzhu Seismic Gap, including the eastern portion of the JQHF, MMSF, and LHSF.