[M-TT36] 雪氷圏地震学: 地震動の解析を通じた雪氷圏における変動の理解

[MTT36-P07] Tidally modulated ice fracture and calving of Langhovde Glacier in East Antarctica

*箕輪 昌紘¹、Podolskiy Evgeny A.²、杉山 慎^1,2 (1.北海道大学・低温科学研究所、2.北海道大学・北極域研究センター)

キーワード：氷震、カービング、南極氷床

Iceberg calving accounts for approximately half of the ice mass loss from the Antarctic ice shelves and floating tongues. Therefore, knowing the triggering mechanisms of ice fracturing and calving is important. Glacier fracturing is a multi-temporal scale process ranging from multi-years to seconds due to glacial stress, tides, waves and hydrofracturing. We measured icequakes with a seismic array composed of three seismometers on the terminus of the ice shelf of Langhovde Glacier in East Antarctica to understand better the tidal fracturing mechanisms of ice shelves and floating tongues. Observed signals were clustered into four waveforms, and their occurrences varied with the tidal variations. Icequakes that occurred during the high tide were the most common, and they had wider frequency ranges between 15 and 100 Hz. Icequakes were also observed during the falling tides, with waveform frequencies centered at around 10 Hz. A beamforming localization suggests that the former icequakes occurred near the ice front, surface depression, and the ice shelf's base. The latter icequakes were more scattered in space, and most of them were located at the ice surface. GPS-derived ice motion was used to model stress distribution along the ice shelf. Near the terminus of the ice shelf, the tide lifted the glacier, resulting in the positive largest principal stress along the base of the glacier near the front. Our analyses highlight that the tidally modulated vertical ice motion is an important mechanism for basal ice fracturing and iceberg calving of ice shelves and floating tongues.