Stress interaction between the two M>6 earthquake since 2016 and its implication on the seismic hazard along the Qilian-Haiyuan fault zone

Qilian-Haiyuan fault zone, the boundary fault zone of the northeastern margin of the Tibetan plateau, regulates the northeastward spreading of the Tibetan plateau and the eastward movement of the Alxa block. Previous work indicates that its effective friction coefficient can be as low as 0.05, which is much less than 0.4 usually assumed and employed in Coulomb stress related seismic hazard analysis. In this paper, we analyzed the Coulomb stress trigging between the 2016 M6.4 Menyuan earthquake and the 2022 M6.9 Menyuan earthquake, as well as the related seismic hazard implication on the northeastern margin of the Tibetan plateau. Our results show that, with the decrease of the effective friction coefficient, the maximum Coulomb stress on the rupture plane of the 2022 M6.9 Menyuan earthquake can reach 0.013 MPa. The result indicated that the 2016 M6.4 Menyuan earthquake could enhance the seismic risk in the hypocenter of the 2022 M6.9 Menyuan earthquake, and the low effective friction coefficient of the Qilian-Haiyuan fault zone have made positive contribution in the stress triggering between the two earthquakes. Our simulations further point out two high Coulomb stress accumulation segments, the Tuolaishan fault in the western and the Tianzhu gap in the central, on the Qilian-Haiyuan fault zone. The high Coulomb stress accumulation segments agree well with the seismic gap and high fault locking, manifests that these segments are at high seismic risk and deserve more attention in the future.