Abstract
Abstract The Tancheng–Lujiang (Tanlu) fault zone is the most active fault zone in eastern China. In this zone, the Anqiu–Juxian fault represents the most recently active fault and has the clearest surface traces and the highest seismic risk. This study comprehensively analyzes the kinematic characteristics of the Jiangsu segment of the Anqiu–Juxian fault using field geological surveys, trenches, shallow seismic reflection surveys, combined borehole section exploration, and middepth seismic reflection surveys. The results show that the Jiangsu segment of the Anqiu–Juxian fault features a single branch in the bedrock outcrop area, with reverse strike-slip motion near North Maling Mountain and Chonggang Mountain and normal strike-slip motion near South Maling Mountain. The sedimentary zone features two normal strike-slip faults (east and western branches), which represent the synsedimentary boundaries of a half-graben rift basin. The kinematic process is represented by rotational movement along the strike-slip fault with a curved path. The resulting tensile and compressive stresses are accommodated by dip-slip movement at both ends of the strike-slip fault. The activity of the Jiangsu segment of the Anqiu-Juxian fault can be divided into two periods. The first period of activity occurred before the later part of the Late Pleistocene, when movement along this curved segment occurred, forming the western branch of the Xinyi segment and the eastern branch of the Suqian segment. The second period of activity started in the later part of the Late Pleistocene and continues today. It is characterized by activity on the western branch of the Xinyi segment and the western branch of the Suqian segment of the Jiangsu segment, while the eastern branch of the Xinyi segment and the eastern branch of the Suqian segment became inactive and can be considered Late Pleistocene faults. The maximum vertical slip rate of the Jiangsu segment of the Anqiu–Juxian fault since the Pleistocene has been 0.28 mm/a. The Jiangsu segment of the Anqiu–Juxian fault formed via dextral strike-slip faulting, mainly due to the southward movement of the region to the east of the fault.
Highlights
The kinematic characteristics of a fault zone are important parameters for studying the activity and behavior of the fault zone and evaluating the earthquake risk
The natural outcrops, geologic trenches, seismic profiles, and combined borehole sections show that the Jiangsu segment of fault F5 is mainly compressional in the areas of North Maling Mountain, the Xinyi River, and Chonggang Mountain
Along the fault in the uplifted area of North Maling Mountain and Chonggang Mountain, the Wangshi Formation sandstone on the side toward the mountain has been thrust onto the Late Pleistocene loess on the side toward the plain, while the Xinyi River shows that the Late Pleistocene calcareous clay layer has been thrust onto the Holocene blackish-brown clay on the western side
Summary
The kinematic characteristics of a fault zone are important parameters for studying the activity and behavior of the fault zone and evaluating the earthquake risk. The Tancheng– Lujiang (Tanlu) fault zone is an important active fault zone and boundary tectonic zone in eastern China, a worldfamous intraplate strike slip fault within a plate, where several large earthquakes of magnitude 7 or higher have occurred since records have been kept. Regarding the kinematic characteristics of the Anqiu–Juxian fault since the Late Pleistocene, some scholars believe that they have involved a combination of thrusting and dextral. Jiang et al [12] used aerial photographs from 1960 and measured the characteristic meterscale horizontal displacement of a gully since the start of the Holocene and inferred a dextral strike-slip rate since the start of the Holocene of 2.2-2.6 mm/a. Li et al [13] calculated a modern strike-slip rate of 0.9-1.2 mm/a using GPS measurement data
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