The Lenglongling fault (LLLF) is located along the northeastern margin of the Tibetan Plateau and forms a part of the Tianzhu seismic gap along the Qilian‐Haiyuan fault zone. Little is known about the recurrence of large earthquakes along the LLLF nor the associated seismic hazards of the gap. Here the six most recent surface rupturing paleoearthquakes of the LLLF are revealed by measurement of offset landforms, trench excavations, and radiocarbon dating. They are labeled E1–E6 from youngest to oldest, and their timings are constrained to the following time ranges: 636–498 to present, 2951–1155, 4016–3609, 5325–4476, 7284–6690, and 8483–7989 years BP, respectively. The LLLF displays evidence of fresh, recent surface rupture, and the trench sections reveal that the fault ruptured to the ground surface during the most recent event. Based on this fresh surface rupture and historical earthquake records, the latest event E1 was most likely the 1927 M8.0 Gulang earthquake. In conjunction with previous studies, Gulang earthquake might be a complicated event characterized by the combined rupture of both strike‐slip and thrust faults. The average recurrence interval of the six paleoearthquakes is 1643 ± 568 years, and the coefficient of variation is 0.34, indicating that the LLLF follows a quasiperiodic recurrence model. Based on this new understanding of the last event, the LLLF may not be a part of the Tianzhu seismic gap. However, an earthquake of up to M_W7.6 could still rupture the gap sections composed of the Jinqianghe, Maomaoshan, and Laohushan faults.

The tectonic crosscutting relationship between the two most tectonic important Xianshuihe-Xiaojiang fault system (XFS) and the Red River fault zone (RRF) is a key basic problem but it is controversial now. These obscure further leads to a hot argument about the geodynamic model of the southeast margin of the Tibetan Plateau. In order to answer whether the XFS has cut across the RRF and extended southwardly, multiple seismological methods, including seismic relocation, b-value analysis, seismic energy, density study, focal mechanism inversion, and regional stress field research, are applied in the Yunnan Province area, China, where the XFS and the RRF intersects with each other. The results comprehensively demonstrate that the southern segment of the XFS has not been affected by the RRF, and it has continued for a length after crossing the RRF, but the Dian Bien Phu fault zone should not be an extension fault of the XFS. Along the SW direction, starting from the middle segment of the XFS, and cutting across the Qujiang fault, Shiping-Jianshui fault zone, RRF, Ailaoshan fault zone, Wuliangshan fault zone, and the southern section of the Daluo fault, the belt should be treated as the eastern boundary of the clockwise rotational in geodynamics model of the Tibetan Plateau in this study area. Based on these conclusion above and previous recognitions, a new geodynamic evolution model is proposed.

Seismic activity frequently occurs in the North China Plain seismic belt. Historical earthquake records for the fault southwest of Beijing are sparse, with only one significant event: the 1057 M 6 earthquake. This study focuses on the southern extension of the Nanyuan-Tongxian Fault. Using dynamic numerical methods, we simulate the rupture process of this earthquake to investigate its impact on strong ground motions in Beijing and surrounding areas. First, on the basis of the fault geometry and hydraulic fracturing stress data, we set the dynamic parameters of the fault plane and construct a curved fault model. Numerical simulation of the dynamic rupture process yielded the following results: a maximum slip of 0.75 m, an average slip of 0.49 m, a rupture duration of approximately 10 s, and a moment magnitude (M_w) of 6.5. The rupture propagated bilaterally; influenced by fault geometric bending, the peak slip rate reached 0.7 m/s on the SW side, whereas the slip rate on the NE side was smoother. The strong ground motion distribution showed a maximum intensity of VIII, which was concentrated along the fault trace with a significant hanging wall effect. Notably, owing to the combined effects of rupture directivity and fault bending, anomalously high-intensity zones appeared in areas distant from the epicenter, such as Shunyi and Tongzhou. This pattern differs significantly from the historical seismic impact pattern of the Sanhe-Pinggu Fault on the northeastern side. Further simulations of the epicenter within the fault indicate that if a future earthquake’s epicenter is located west of the fault center, Tongzhou would still face high-intensity ground motion risks. The results from both planar-fault and 3-D velocity-model simulations further demonstrate that strong ground-motion characteristics are influenced by multiple factors. This study reveals the unique seismogenic mechanism of the Nanyuan-Tongxian Fault, providing a key basis for seismic hazard assessment southwest of Beijing.