Joint inversion of active sources and ambient noise for near-surface structures: a case study in the Balikun Basin, China

The multichannel analysis method of surface waves (MASW) is widely used to image S-wave velocities (V_S) of the near surface. The MASW method can typically image V_S structures at depths down to several tens of meters. However, this investigation depth is insufficient to meet the requirements of some engineering projects. Ambient noise tomography (ANT) is an appealing alternative method to map greater depths due to its ability to obtain low-frequency surface waves from ambient noise. Combining active and ambient noise surface-wave measurements helps to extend the investigation depth of near-surface V_S structures. In this study, we develop a joint inversion method of combining active sources and ambient noise in a near-surface S-wave velocity investigation. We demonstrate the effectiveness of our methods using data from a surface-wave survey project in the Balikun basin, China, as a case study. We extract dispersion curves of fundamental-mode Rayleigh waves from the active source and ambient noise survey, respectively. We combine these two sets of dispersion curves to determine local Rayleigh-wave dispersion curves. Finally, we build a 2D V_S model beneath the Balikun basin by inverting the resulting local dispersion curves. Our results demonstrate that combining these two sets of dispersion curves from active and ambient noise data is an effective approach to increasing investigation depth of near-surface structures.