1. College of Geo??Exploration Science and Technology, Jilin University, Changchun 130026, China; 

 To address the challenge of long?duration data collection difficulty in urban geophysical exploration resulted from regulatory restrictions on exploration sites, the authors utilize ultra?short?duration passive source noise data. By employing the phase?weighted stacking of cross?correlation functions, dispersion curves are extracted. The fundamental mode dispersion curves are then inverted to obtain a one?dimensional S?wave velocity profile. Utilizing this profile as an initial model, a second?stage inversion is conducted, which reveals the presence of underground cavities. The results of this study demonstrate the feasibility of using ultra?short?duration passive source surface? wave imaging for cavity detection.