Offshore microtremor array measurements for a wind farm site investigation
Year: 2025
Type: article
Abstract: We develop an offshore microtremor array measurement (MAM) system that can easily determine the VS profile below the seafloor that is needed for the design of fixed-bottom offshore wind farms. In our system, four ocean-bottom seismometer sensors are installed at the vertices and circumcenter of an equilateral triangle on the seafloor to measure microtremors. Dispersion curves are calculated from observed microtremors using the spatial autocorrelation method, and the VS profile is obtained by an inverse analysis of the dispersion curves. Exploration using offshore MAM started in earnest in 2019 and has been carried out in more than 250 locations in Japan by the end of 2023. The results of these explorations have been effectively used in the inspections conducted by a wind farm certification society. Because the offshore MAM cannot accurately obtain VS in the shallow layer (20 m or less), we have also developed a triangular miniature array MAM equipment with a base length of 1 m. It is confirmed that an approximate VS value in the shallow layers can be obtained by processing the data obtained using this equipment with the centerless circular array method, but it is considered difficult to put this method to practical use at this time because it is too sensitive to incoherent noise. We develop another offshore MAM (linear array MAM) suitable for floating offshore wind farms, which is installed at a greater depth than the bottom-fixed types. The test measurements conducted at two offshore locations confirm that the linear array MAM can also obtain clear dispersion curves and VS profiles. It is also confirmed that the active surface wave method, which can obtain VS of shallower layers than offshore MAM, is possible by dropping a weight on the extension line of the linear array.
Source: Interpretation
Authors: Yoshikazu Matsubara, Yasuhiro Asano, Mikihiro Imai, Yusuke Inoue, Akeshi Hiraide
Institution: OYO Corporation (Japan)
Language: English
Topic: Seismic Waves and Analysis
Subfield: Geophysics
Field: Earth and Planetary Sciences
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W4410104025