Characteristics of Background Noise on Regional Seismic Measurement Stations in Ports

The Ministry of Oceans and Fisheries of Korea has installed port seismic monitoring stations, mainly at major domestic trade ports, to enable rapid response to unpredictable earthquakes. Currently, 27 stations operate across 13 ports, including 10 along the West Coast, 10 along the South Coast, and 7 along the East Coast. This study analyzed regional background noise levels using continuous microtremor data collected from 2022 to 2024, based on the Probabilistic Power Spectral Density method. Owing to the soft ground typical of port sites, each seismic station is configured as a paired system consisting of a surface station and a vertically aligned borehole rock station. Results show that surface stations exhibit higher and more variable noise levels within the artificial noise band characteristic of industrial ports compared with borehole stations. Additionally, noise levels remain consistently high across all sites in the mean-period frequency band. The Incheon Port bedrock station demonstrated the lowest and most stable noise characteristics, suggesting its suitability as a reference station for future Horizontal-to-Vertical Spectral Ratio analyses. These findings highlight the importance of quantitative background noise assessment to ensure high-quality seismic data and provide a basis for evaluating site response and long-term noise variability at port facilities.