The Multichannel Analysis of Surface Waves (MASW) method is a seismic geophysical testing technique that relies on the generation and propagation of surface waves (Rayleigh and Love waves) to characterize subsurface stiffness. As MASW has grown in popularity for geophysical and engineering applications, several studies have examined various aspects of the methodology, including effects of seismic source, testing configuration, and data processing methods. Theoretically, Rayleigh and Love waves are best generated using vertical and horizontal impacts, respectively. Angled impacts are capable of generating both Rayleigh and Love waves simultaneously. However, it is unclear the extent with which variations in the impact angle quantitatively affect signal quality for Rayleigh and Love waves. Therefore, there is uncertainty regarding the optimal angle of impact for simultaneous generation of Rayleigh and Love waves. The current paper presents a field case study that was performed using Rayleigh and Love waves generated at various angles of impact. Results indicated that Love wave energy transfer and the corresponding dispersion images had less sensitivity to the angle of impact. In contrast, the quality of the Rayleigh wave dispersion images improved as the impact angle was less vertical despite less relative energy transfer to the ground. In this case, impact angles closer to vertical generated more Rayleigh wave power, but tended to excite higher modes, which obscured the fundamental mode in the dispersion image. The results suggest that simultaneous generation of Rayleigh and Love waves should proceed with impact angles favoring the generation of Love waves (i.e., more horizontal) in order to optimize signal quality. However, at sites with significantly less higher mode excitability, it may be possible to focus more on Rayleigh wave generation (i.e., impacts closer to vertical) and still acquire high quality Love wave data.
Presentation Date: Tuesday, October 16, 2018
Start Time: 8:30:00 AM
Location: 204A (Anaheim Convention Center)
Presentation Type: Oral