Seasonal crustal movements in Northeast Japan revisited

Abstract

Seasonal movements of global navigation satellite system (GNSS) stations in Northeast (NE) Japan are mainly driven by elastic loading of snow, reaching a few meters deep along the western flank of the backbone range. Here we study them in a comprehensive manner to solve remaining problems. GNSS stations in the inland area show sharp and strong subsidence peaks in winter and remain flat in other seasons, a response consistent with the snow loading. On the other hand, those close to coasts show broad and weak winter subsidence peaks. This needs additional loads in spring to retard the rapid decay of snow loading. We propose that rice fields work as natural reservoirs until early summer and evaluate quantitative consistency of the hypothesis. We also found that some stations show abnormally large winter subsidence that cannot be explained by snow loading alone. Here we examine two factors, i.e., groundwater extraction in winter for melting snow on roads, and snow accretion onto GNSS antenna radomes. We also evaluate seasonal ocean water mass changes in the Japan Sea using GRACE satellite gravimetry data. We found its role in seasonal crustal movements in NE Japan quite small.