Combined active-passive surface wave measurements at five sites in the Western and Southern US

Abstract

Generally, two types of sources, active and passive, are used in surface wave tests. Typical examples of active sources are a hammer, dropped weight, and harmonic shaker. A reasonably portable active source is often limited in its ability to sample deep soils due to the difficulty in generating low-frequency energy. Passive surface waves such as those of microtremors and cultural noise may be utilized as an alternative to overcome this limitation because passive waves typically contain greater energy at low frequencies than most active surface waves. In addition, active and passive measurements may be combined to enable shear wave velocity (VS) profiling to greater depths without sacrificing near-surface resolution. In this study, surface wave tests with active and passive sources were performed at five different sites in the western and southern US by using different test parameters. Dispersion curves from the active and passive measurements at each site were compared and combined to develop a composite dispersion curve. The composite dispersion curve was then inverted to obtain the VS profile. The results show that combined active-passive measurements significantly enhance the capabilities of the surface wave method in its deeper soil sampling.