Muographic Detection of Seasonal Variations in Astronomical Tides With Hyper Kilometric Submarine Deep Detector (HKMSDD)

Tidal amplification or tidal reduction as a response to sea-level variations can potentially amplify or mitigate the flood risk associated with future sea-level rise caused by global climate change. Tokyo Bay Seafloor Hyper Kilometric Submarine Deep Detector (TS-HKMSDD), the world’s first detector array located underneath the seafloor, has operated without intermittency for more than one year collecting cosmic-ray muon data, which revealed the seasonal variations in astronomical tides in Tokyo Bay. By comparing onshore tide gauge seasonal mean sea level data with offshore-subseafloor TS-HKMSDD data, it was found that seasonal water level rises in Tokyo Bay played a negative role in the local tidal amplification, indicating that future sea-level rise may potentially mitigate the flood risk in the Tokyo Bay area. With its cosmic sensors, which can monitor aquatic environments without requiring them to be in direct contact with water and in conjunction with the availability of globally increasing urban underground spaces (UUS) for installation (including pre-existing underwater tunnels and commercial buildings that offer reliable utilities in coastal areas) we anticipate that the robustness and versatility of HKMSDD as a long-term stable tide monitor will make it a world standard measurement tool for coastal tide monitoring to complement pre-existing tide gauge stations worldwide