关键词: 王湖断层, 空间展布, 活动时代, 分段, 盆地边界

Abstract:

The Wanghu Fault is a major geological structure in Jinzhong City, Shanxi Province, traversing the Yuci urban area. Previous studies suggested that the fault originated in the Late Pleistocene, extending approximately 17.0km from Nanguan in the south to Dongshagou in the north, with a NNW strike and SW dip. However, previous research was primarily based on hydrogeological and seismic safety assessments, lacking detailed investigation into the fault’s structural characteristics and activity history—particularly regarding definitive evidence of its active period. This uncertainty has posed challenges for disaster prevention and urban planning in Jinzhong City.

To address this gap, an integrated investigation was conducted combining shallow seismic exploration, field geological surveys, and borehole-profile studies. In the northern section—located in the Yuci urban area where morphological features are indistinct—shallow seismic imaging, borehole profiling, and chronological testing were employed to delineate the fault’s position and assess its activity. In the southern section near Donghao and Liutai villages, where topographic contrast between mountainous and basin terrain is more pronounced, field geological surveys and age-dating methods were used to trace the fault along the geomorphic boundary.

The results reveal that the Wanghu Fault is a complex fault zone composed of multiple strands, forming the eastern boundary of the southern Taiyuan Basin. It extends approximately 27.0km, strikes nearly N-NNW, dips west to southwest at 45°~60°, and is classified as a normal fault with a dextral(right-lateral)slip component. The fault has been active since the late Middle Pleistocene. It comprises two segments:

The northern segment, concealed beneath urban cover, begins at Xiaoyukou Village and connects with the eastern segment of the Tianzhuang Fault. It passes through Sucun, Niedian, Beiguan, and Dadongguan villages, intersecting the Xiaohe Fault. It trends nearly N-S, dips westward, with a minimum displacement of 4.46~4.79m, and spans 16.0km.

The southern segment is exposed in the Loess Plateau area, beginning north of Donghao Village and extending southeast through Beizhao, Yuchengping, and Liutai Villages. It strikes NNW, dips southwest at 60°~75°, with a minimum displacement of 0.7~1.3m, and is about 11.0km long.

Analysis of fault location, activity period, and gravity anomaly data indicates that the Wanghu Fault marks the Quaternary structural boundary at the northeastern margin of the Taiyuan Basin. Together with the Jiaocheng Fault to the west and the Taigu Fault to the southeast, it outlines a semi-fan-shaped fault-controlled basin, deeper in the west and shallower in the east. This finding challenges previous interpretations that the basin’s northeastern boundary was merely a depositional interface between Late Cenozoic fluvial-lacustrine and loess sediments, lacking any associated faulting. Furthermore, it revises the timing of fault activity from the previously assumed Late Pleistocene to the Middle Pleistocene. These findings are critical for earthquake hazard mitigation, urban development, and land-use planning in Jinzhong City. They also provide valuable insights into the tectonic evolution and seismic potential of the Taiyuan Basin.

Key words: Wanghu Fault, spatial distribution, activity age, segmentation, basin boundary