[S-GD01] Geodesy and Global Geodetic Observing System

[SGD01-12] Crustal subsidence as the elastic response to the SWJ heavy rain in 2020

*Kosuke Heki¹, Syachrul Arief² (1.Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, 2.Indonesia Geospatial Information Agency)

Keywords:vertical crustal movement, SWJ heavy rain, loading

Stationary weather fronts lying along the southwestern Japan (SWJ) often bring disastrous heavy rains in early summer. Here we study three past heavy rain episodes in 2017 July, 2018 July, 2019 August, and the latest episode in 2020 July, and study lithospheric deformation due to the rainwater loads. The water loads depress the land surface and let crust subside, and we study them using the F5 solutions of the GEONET station coordinates using methods used to study the 2019 typhoon Hagibis (Zhan et al., 2021 JGR submitted). After applying a network filter to remove common mode errors, we confirmed subsidence of 1-2 cm in multiple regions where severe flood occurred. Such subsidence was observed to recover with a time constant of 1-2 days reflecting rapid drain of rainwater to ocean due to large topographic slope and proximity to the sea. In Zhan et al. (2021), we estimated the distribution of surface water from crustal subsidence data using the Green’s function for a point load. We then found that topographic concavity of GNSS stations in Japan (tend to be installed along valleys and within basins) causes overestimation of the water mass. In this study, we focus more on the correlation between subsidence of GNSS stations and precipitation at nearby rain gauges in a long time series. We will highlight following issues, (1) time constant of rainwater staying in situ, (2) difference in crustal response to rainwater load between GNSS stations with different topographic and geologic settings, (3) contribution of rain loads to day-to-day variabilities of vertical position of GNSS stations.