A Single-Point Interference Method for Subsurface Structure Estimation Using a Six-Component Seismometer

Seismic surveys commonly use sensor arrays to record wave signals, with methods like noise cross-correlation function and spatial autocorrelation to analyze wave propagation features. However, these multi-station methods require many sensors, leading to high costs and deployment complexities. In contrast, single-station methods utilize constraints among different seismic components at a single location to extract dispersion curves and invert subsurface structures. However, these methods face theoretical limitations, including a lack of a generalized model to determine which components should be used, and problems related to the non-unique inversion of dispersion curves. To address these limitations, we propose the single-point interference method, using a six-component seismometer including an interferometric fiber-optic gyroscope to record rotational motions. This method models wave propagation as a two-port network system, and uses a transfer function to describe wave interference at the measurement point, where specific input-output pairs correspond to distinct subsurface structures. Assuming a single-source plane wave, when the transverse acceleration component serves as the input and the vertical rotation component as the output, the transfer function defines local parameters of Love waves: its amplitude represents the local phase velocity, and its phase represents the back azimuth of the incident wave. By adjusting input-output combinations, this method obtains the subsurface velocity structures for different wave types. For example, with the vertical acceleration component as the input and the transverse rotation component as the output, the local phase velocity of Rayleigh waves can be derived. This method provides an opportunity to cross-validate the inversion results. The term single-point emphasizes the locality of the method, rather than limiting its application to just one measurement point. By applying a six-component seismometer to obtain inversion results at multiple points along a line and interpolating these results, a continuous subsurface profile can be constructed. Expanding the line to a grid of points enables 3-D modeling of the subsurface structure within the grid area. Experiments demonstrate that this method can estimate velocity structures with a single-station seismometer, reducing the costs and deployment complexities of multi-station methods. Experimental seismic records and corresponding local velocity structure estimations will be presented to demonstrate this method’s advantages in seismic surveys.