Abstract
The Mufushan-Jiaoshan fault (MJF) is a hidden active fault located on the north side of the Ningzhen Mountain Range and developed along the Yangtze River in Zhenjiang area, China. In this paper, the structure of MJF is detected and studied using group-velocity ambient noise tomography. In the study area (18 km × 25 km), 47 short-period seismic stations were deployed with the average station spacing of about 3 km and 24 days (from 27 February to 22 March 2019) of continuous ambient-noise recordings were collected. And 510 group velocity dispersion curves in the period band 0.5–5 s were extracted using the vertical component data. And then the three-dimensional shear-wave velocity structure was inverted using group dispersion data by the direct surface-wave tomographic method. Our results are consistent with the geological background of the study area, showing that in the depth range of 0.6–1.5 km, the north side of MJF presents a relatively high velocity, and the south side presents a distribution pattern of high and low velocity. While in the depth range of 1.5–2.0 km, the shear-wave velocity (Vs) model is relatively simple with relatively low velocity on the north side and relatively high velocity on the south side. And the gradient zone of Vs may be the location of the main fracture surface of MJF. The good correspondence between the Vs model and the fault structure indicates that the ambient noise tomography method can be used as an effective method for detecting hidden faults in urban environments.
Highlights
The Mufushan-Jiaoshan fault (MJF) is a hidden active fault located on the north side of the Ningzhen Mountain Range and developed along the Yangtze River in Zhenjiang area, China
In order to detect the structure of the Mufushan-Jiaoshan fault (MJF), which is located in the urban area of Zhenjiang, China, and the location of its main fracture surface, 47 stations were installed across the Yangtze River and continuous ambient-noise data for 24 days were collected
Taking MJF as the boundary, the Vs on the north side is distributed in the near north–south direction with relatively low velocity, which may be related to the Yizheng depression, while on the south side, it is distributed in the near east–west direction with relatively high velocity, which could be related to the Ningzhen Mountain Range (NMR); (2) Starting from the depth of 1.0 km, two high-velocity anomalies with a velocity of about 3.3 km/s began to appear in the northwest and southeast of the study area, and extended to the center forming a whole at a depth of 1.6 km
Summary
The Mufushan-Jiaoshan fault (MJF) is a hidden active fault located on the north side of the Ningzhen Mountain Range and developed along the Yangtze River in Zhenjiang area, China. Using ambient noise tomography (ANT) with a reasonable array design, we can get the highresolution subsurface structure in a certain depth range without conducting active source experiments and may obtain the structure of the hidden faults before earthquakes occur. In order to detect the structure of the Mufushan-Jiaoshan fault (MJF), which is located in the urban area of Zhenjiang, China, and the location of its main fracture surface, 47 stations were installed across the Yangtze River and continuous ambient-noise data for 24 days (from 27 February to 22 March 2019) were collected. The Zhenjiang area has a complex terrain, with the new Yangtze River Delta plain in its northern and eastern parts, low mountains and hills in its central part, and landform in its southern part (Fig. 1)
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