Seismic surface wave method for subsurface layered soil exploration

Abstract

Subsurface soils in the vadose zone are layered structures. Typically, there are three distinctive layers at the depths of a few meters, featuring as a top rigid layer (due to surface crusting and sealing), a middle soft zone (due to soil moisture), and a region with stiffness increasing with depth (due to increased overburden pressure). The properties of subsurface soils in the vadose zone are often altered by natural events (weather and chemical reactions) or cultural activities (compaction). The exploration of the subsurface soils is required for agricultural, environmental, civil engineering, and military applications. In this talk, a seismic surface wave technique is developed, a so-called high frequency multi-channel analysis of surface wave method (HF-MASW). In the method, an electromagnetic shaker is placed on the ground and serves as a seismic source, a vibration sensor (either a laser Doppler vibrometer or an accelerometer) is used to record surface vibrations at multiple locations alone a straight line. Rayleigh waves propagation theory, layered structural modeling, and spectral analysis are applied for processing received signals and conducting inversion. A soil profile in terms of shear wave velocity is determined from the method. In this talk, several applications using MASW method will be reported, including layering delineation with cross-section imaging, weather effects monitoring, fragipan detection, and surface crusting and sealing evaluation.