[S-GD02] Geodesy and Global Geodetic Observing System

[SGD02-11] Transient crustal subsidence by the 2024 September heavy rain episode in the Noto Peninsula: Rainwater loads remain in the ocean?

*Kosuke Heki¹, Shuo Zheng² (1.Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, 2.Hong Kong Polytechnic University)

Keywords:GNSS, 2024 heavy rain in Noto Peninsula, rain loading, subsidence

Crustal response to the 2024 September heavy rain episode in the northern Noto Peninsula, Central Japan, was studied using a dense network of global navigation satellite system receiving stations. Regionally integrated subsidence was proportional to the daily rain, i.e., ~0.1 km³ volumetric subsidence occurred in response to 1 Gt daily rain. The subsidence lasted for only a day or so. These findings are consistent with past cases of elastic response of the Japanese Islands lithosphere to rain loading. We also found that a tiny island (Hegura-jima), to the north of the peninsula, also subsided by a few centimeters on heavy-rain days. This cannot be explained by terrestrial water storage loads within the island. Rainwater may have remained partly in the ocean surrounding the island depressing the ocean floor as a surface load. We address this problem comparing tide gauges, atmospheric pressures, precipitations, and crustal movements in nearby areas.