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[SGD02-05] On the detection of step-like crustal subsidence due to heavy snowfall events
Keywords:GNSS, surface load, crustal subsidence, heavy snowfall event
Temporary subsidence signals of GNSS stations in Japan by the 2019 typhoon Hagibis and 2018-2020 summer disastrous rainfall episodes in SW Japan have been detected by Zhan et al. (2020 JGR) and Heki & Arief (2021 EPSL), respectively. Such crustal subsidence due to rainwater loads in Japan lasts for only a day or so reflecting rapid run-off of rainwater to ocean. Hence, rainwater load does not much contribute to seasonal crustal movements. On the other hand, winter snow remains on the ground for months as snowpack and brings seasonal crustal movements in snowy regions (Heki, 2001 Science).
Large snowfall events in winter would make step-like crustal subsidence over a large region, and vertical position time series during a winter would include multiple signatures of such episodes. However, crustal movements due to snow load have been studied mainly in seasonal timescales, and subsidence steps associated with heavy snowfall events have never been detected even after correcting for common mode errors. This is due to several difficulties such as, (1) cancellation of subsidence by snow loads by the negative change of atmospheric loads often associated with such events, and (2) occurrences of fake subsidence signatures due to snow accretion to radomes of GNSS stations.
The first problem could be solved by correcting for subsidence due to atmospheric load changes using a GFZ product called NTAL (non-tidal atmospheric loading). Regarding (2), we could remove such fake subsidence signals by using changes in signal-to-noise ratio (SNR) of microwave signals from GNSS satellites, which are found to be proportional to the amounts of fake subsidence (Heki & Jin, 2023 Sat. Nav.). Here we report a few examples of large snowfall events in 2022 January and February in Hokkaido and successful detections of step-like subsidence of GNSS stations by these new approaches.
Large snowfall events in winter would make step-like crustal subsidence over a large region, and vertical position time series during a winter would include multiple signatures of such episodes. However, crustal movements due to snow load have been studied mainly in seasonal timescales, and subsidence steps associated with heavy snowfall events have never been detected even after correcting for common mode errors. This is due to several difficulties such as, (1) cancellation of subsidence by snow loads by the negative change of atmospheric loads often associated with such events, and (2) occurrences of fake subsidence signatures due to snow accretion to radomes of GNSS stations.
The first problem could be solved by correcting for subsidence due to atmospheric load changes using a GFZ product called NTAL (non-tidal atmospheric loading). Regarding (2), we could remove such fake subsidence signals by using changes in signal-to-noise ratio (SNR) of microwave signals from GNSS satellites, which are found to be proportional to the amounts of fake subsidence (Heki & Jin, 2023 Sat. Nav.). Here we report a few examples of large snowfall events in 2022 January and February in Hokkaido and successful detections of step-like subsidence of GNSS stations by these new approaches.