日本地震学会学, 日本測地学会学長

Basal conditions of the Greenland Ice Sheet (GrIS) are a key research topic in climate change studies. The recent construction of a seismic network provides a new opportunity for direct, real-time, and continuous GrIS monitoring. Here we use ambient noise surface wave data from seismic stations all over Greenland for a 4.5-year period to detect seismic velocity changes beneath the inter-station lines. We observe clear seasonal/long-term velocity changes for many station pairs, and propose a plausible mechanism for the velocity changes. The dominant factors causing these changes might be pressurization of both the GrIS and underlying crust by seasonal/long-term snow accumulation, and depressurization by ice thinning due to GrIS flow and ice mass loss. However, heterogeneity in GrIS basal conditions might impose strong regionalities on the results. An interesting feature is that, even at adjacent station pairs in the inland GrIS, both velocity decrease and increase can be caused by snow accumulations. The former pair might be located on a thawed bed that decreases velocity by increased meltwater due to pressure melting, whereas the latter pair might be located on a frozen bed that increases velocity by compaction of ice and bedrock. The results suggest that surface waves are very sensitive to the GrIS basal conditions, and further observations will contribute to a more direct and quantitative estimation of water balance in the Arctic region.