In the Atosanupuri volcanic complex in the Kussharo caldera, eastern Hokkaido, Japan, short-term uplift followed by subsidence around 1994 was detected using interferometric SAR (InSAR) analysis. In this study, an InSAR time series analysis from 2014 to 2022 using the ALOS-2 satellite revealed continued long-term subsidence of the entire Atosanupuri volcanic complex. The subsidence followed an exponential trend, with a relaxation time constant of several decades. However, long-term data are required to determine future displacement convergence due to frequent temporary and unsteady stagnations and uplifts. In contrast, the northwestern part of the Rishiri lava dome showed a constant subsidence rate without fluctuations. The results of the InSAR time-series analysis from 2016 to 2020 demonstrated that a horizontal sheet-like crust (sill) located 5.3 km below the surface of the Atosanupuri volcanic complex is shrinking at a rate of −1.44 million m3/year, whereas another sill at a depth of 700 m below the surface of the northwestern part of the Rishiri lava dome is shrinking at a rate of −21,000 m3/year. Although the residuals after subtracting these pressure source models indicate displacements of a few millimeters per year, these are most likely systematic errors inherent in InSAR. The InSAR time series analysis proved to be highly accurate in capturing temporal changes and spatial distribution, even when the displacement is less than 1 cm per year, and the results were not easily confounded by various errors. Therefore, data accumulation is crucial for InSAR time-series analysis.
