Study on the Heterogeneity of the Stress Field in the Maduo Earthquake Fault Zone

The 2021 Maduo earthquake sequence occurred on the Jiangcuo fault zone in Qinghai, China. However, the earthquake sequence did not occur along a straight fault. Aftershocks in the southeast section deflected the aftershocks in the southeast section to the east, when the aftershocks in the northwest section bifurcated. To investigate the relationship between these eastward deflections, aftershock bifurcations, and fault activity, 150 focal mechanism solutions of the Maduo earthquake sequence are collected and processed, and then the stress fields in the subregion and whole region are subsequently determined by partitioning the sliding window from southeast to northwest. The results show that the overall tectonic stress field of the Maduo earthquake sequence exhibits northeast–southwest compression and northwest–southeast extension due to the northward compression of the Indian plate, causing rupture of the Kunlunshankou-Jiangcuo fault, which straightened the curved Maduo-Gander fault. The stress field at the deflection of the southeastern section of the source area differs significantly from the overall stress field. The plunge angle of the extensional stress axis in the southeastern deflection area is close to vertical, which is speculated to be due to the effect of the crack tip and the adjustment of local stress after the earthquake. The extensional stress axis at the bifurcated distribution of aftershocks in the northwestern section of the source area is slightly greater than of the overall stress field, indicating that the activation of the bifurcated hidden fault was triggered by the high rupture intensity and the adjustment of local stress. The reactivation of the hidden bifurcated fault results in local stress and causes decreasing seismicity west of the bifurcation area.