Progressive strategies of single-channel seismic survey for geological characterization assessment in urban areas

Abstract The application of geophysical methods in urban underground spaces, where geological complexity and potential disasters coexist, poses a technological challenge for geophysicists. Theoretically, many geophysical methodologies can be employed to investigate shallow subsurface geological structures. However, their usage is restricted by low resolution, shallow penetration depth, as well as the congested urban environment and various interfering factors. With the aim of safeguarding the constructed environment, a progressive single-channel seismic strategy was developed. A comparative experiment was conducted to assess the advantages of the rare earth giant magnetostrictive transducer sources. Subsequently, the spectra and penetration depths were calculated, and a detailed analysis of the profiles obtained from two types of sources was performed. A case study is presented here, focusing on a collapse zone between Jinggang Station and Shazikou Station on Metro Line 4 in Qingdao. This study's results show that the new single-channel approach possesses these traits: (i) higher resolution and greater penetration depth (up to 100 m), (ii) resistance to noise interference, (iii) good consistency among seismic traces, and (iv) ease of operation, high work efficiency, and environmental friendliness. The successful application of our approach clearly reveals subsurface images and showcases its capability, thus offering valuable practical insights for identifying shallow subsurface geological features in complex urban environments.