Activity variations of the Shanzuokou-Sihong fault within the Jiangsu segment of the Tancheng-Lujiang fault zone and their origins

The Shanzuokou-Sihong fault, having undergone the entire evolutionary process of the Tancheng-Lujiang fault zone (also referred to as the Tancheng-Lujiang fault zone), exhibits segmentation during the latest activity epoch. Determining the location and origin of its activity segmentation will provide a significant reference for exploring the activity variations of its branch faults and their origins. This study investigated the activity of the Shanzuokou-Sihong fault using a three-dimensional approach combining field geological surveys, shallow seismic exploration, and crosswell stratigraphic correlation. The results show that the Shanzuokou-Sihong fault is a Late Pleistocene active fault on the east side of the North Maling Mountain and a Middle Pleistocene fault in Xinyi City. Moreover, a Late Pleistocene-Early Holocene active fault has been discovered recently at the Zhangcang Primary School in Xinyi City (also known as the Zhangcang Primary School fault). With the intersection of this newly discovered fault and the Shanzuokou-Sihong fault (northeast of Zhangcang Village) as demarcation, the Shanzuokou-Sihong fault can be divided into northern and southern segments, which are a Late Pleistocene active fault and an Early-Middle Pleistocene fault, respectively. Since the Late Pleistocene, the northern segment has extended southward to the Zhangcang Primary School fault due to fault activity. The North Maling Mountain is a bedrock massif within the Tan-Lu fault zone, distributed along the strike of the fault zone. Its continuous uplift since the Quaternary has a certain coupling relationship with the activity variations of the Shanzuokou-Sihong fault. This study will provide a valuable reference for understanding both the activity variations of other branch faults and the formation mechanism of hills and mountains in the Tancheng-Lujiang fault zone.