The subsidence is thought to be due to the elastic deformation of the earth due to the load of rainwater, and was particularly remarkable in the heavy rains in July 30 and the heavy rains in July 7.The winter crustal movement of the Japanese archipelago due to snow load was known by precise position measurement using a positioning satellite 2 years ago, but it is difficult to analyze because the crustal movement due to rain continues only for a short period of time, and it has been difficult to detect so far. was.

　This time, the research group uses the GNSS observation network operated by the Geospatial Information Authority of Japan.Careful removal of apparent fluctuations from the GNSS station's vertical position time series, including before and after the flood, reveals a 1-2 cm subsidence associated with the flood load.In this study, the subsidence of the GNSS observation station was compared with the data of the AMeDAS rain gauge operated by the Japan Meteorological Agency, and the proportional relationship between them was found.

　When the amount of rainfall and the amount of sedimentation are calculated as the total of a wide area such as the whole of western Japan, there is a proportional relationship that the ground sinks by a little less than 1 cm when it rains 100 mm a day.It was also found that the rivers in Japan are short and steep, and the speed at which rainwater flows into the sea is high, so these sediments recover and recover in about one day after heavy rains.

　So far, the cause of the anomalous subsidence often seen above and below the GNSS station has been a mystery, but this result shows that a significant portion of the subsidence is due to the load of rainwater, due to the actual deformation of the solid Earth. It has been found.In the future, it is expected that the understanding of detailed position changes of GNSS stations will progress.

Paper information:[Earth and Planetary Science Letters] Trustal response to heavy rains in Southwest Japan 2017-2020