## 4 Results
### Results of Coulomb Failure Stress Changes
The \(\Delta CFS\) generated by the four events in 2023 reveals a zone of decreasing Coulomb stress in the AB vertical near the B side, but adding the 2020 6.8 \(M\)w earthquake to the calculation reveals that the Coulomb stress turns out to be increasing in this region. Figure 4 illustrates the \(\Delta CFS\) induced by eight earthquakes on the vertical plane at different latitudes (specific calculated values see Table S5 in Supplementary Materials). Column (a) represents the \(\Delta CFS\) induced by four earthquakes during the period 1986-2020; column (b) represents the \(\Delta CFS\) generated by four earthquakes occurring in 2023; and column (c) represents the \(\Delta CFS\) produced by eight earthquakes combined. An observation of the 39\({}^{\circ}\) N vertical plane reveals that the 2023 earthquakes reduced the original stress  
Figure 4: \(\Delta CFS\) in the vertical plane. (**a**) \(\Delta CFS\) generated by earthquakes (\(\geq\)6 \(M\)w) occurring in 1986–2020; (**b**) \(\Delta CFS\) generated by earthquakes (\(\geq\)6 \(M\)w) occurring in 2023; (**c**) \(\Delta CFS\) generated by earthquakes (\(\geq\)6 \(M\)w) occurring in 1986–2023. increasing area in the 39\({}^{\circ}\) E-40\({}^{\circ}\) E range and created a stress-reducing area. The large Coulomb stress change area in the 39\({}^{\circ}\) N vertical plane is concentrated in the 40\({}^{\circ}\) E-41\({}^{\circ}\) E range and was induced by the 6.3 \(M\)w earthquake in 2003. The mean positive \(\Delta CFS\) in the 40\({}^{\circ}\) E-41\({}^{\circ}\) E range of 39\({}^{\circ}\) N vertical plane is about 0.86 bar, and the mean negative \(\Delta CFS\) is about \(-\)0.97 bar. The 2023 earthquake produced enormous Coulomb stress changes in the 38.5\({}^{\circ}\) N vertical over a range of 35\({}^{\circ}\) E-39\({}^{\circ}\) E, with a major Coulomb stress increase induced close to the west and a primary Coulomb stress reduction zone close to the east. However, the more extensive Coulomb stress changes in this vertical plane were induced by the 2020 6.8 \(M\)w earthquake with averaging positive and negative \(\Delta CFS\) values of about 0.47 bar and \(-\)0.36 bar, respectively. The \(\Delta CFS\) map for the 38.35\({}^{\circ}\) N vertical plane is similar to that for the 38.5\({}^{\circ}\) N. However, the \(\Delta CFS\) in the 38.35\({}^{\circ}\) N vertical plane is more pronounced than in the 38.5\({}^{\circ}\) N plane. Because the 38.35\({}^{\circ}\) N plane is closer to the sources of the destructive 7.7 \(M\)w and 7.6 \(M\)w earthquakes of 2023 and the 6.8 \(M\)w earthquake of 2020 than the 38.5\({}^{\circ}\) N plane. Interestingly, this vertical has several distinct dividing lines between increasing and decreasing Coulomb stress. \(\Delta CFS\) are significant on both sides of these dividing lines, the difference being that \(\Delta CFS\) values are positive on one side and negative on the other. The mean \(\Delta CFS\) values in this vertical plane are about 0.78 bar and \(-\)0.76 bar. The range of \(\Delta CFS\) induced by the four earthquakes during 1986-2020 in the 38\({}^{\circ}\) N vertical is not extensive, and the values are small. However, the 7.6 \(M\)w earthquake in 2023 induced tremendous Coulomb stress changes in this vertical plane. There is a region of negative \(\Delta CFS\) values in the 36\({}^{\circ}\) E-38\({}^{\circ}\) E range. Immediately adjacent to this zone of reduced stress is a zone of increased stress. In this vertical plane, the Coulomb stress increment due to the 7.6 \(M\)w earthquake averaged about 3.7 bar, and the Coulomb stress decrease averaged about \(-\)2.9 bar. The areas with large \(\Delta CFS\) values are concentrated within 50 km of the ground surface. The \(\Delta CFS\) values become progressively smaller at depths greater than 50 km. The range of \(\Delta CFS\) induced by the 6.0 \(M\)w earthquake in 1986 in the 37.7\({}^{\circ}\) N vertical plane is not extensive.