[U-03] Cryoseismology - a new proxy for detecting surface environmental variations of the Earth -

[U03-03] Ambient seismic noise at a Himalayan debris-covered glacier

*Evgeny A. Podolskiy¹、Koji Fujita²、Sojiro Sunako²、Akane Tsushima³、Rijan Bhakta Kayastha⁴ (1.Arctic Research Center, Hokkaido University、2.Graduate School of Environmental Studies, Nagoya University、3.Research Institute for Humanity and Nature, Kyoto, Japan、4.School of Science, Kathmandu University)

キーワード：debris-covered glacier, thermal stress, seismic noise

Seismic data was collected during autumn 2017 at a debris-covered glacier in the Himalayas to provide a wide-scale characterization of its cryo-seismic wavefield. Here, we analyze ambient noise at the glacier and find a strong diurnal variation of seismicity. We show that the air temperature is pacing the intensity of broadband noise (0.1-100 Hz) and that its polarity depends on an existence or a lack of a debris-mantle. Debris-covered area has the highest activity in the afternoon, while debris-free area at night. We consider debris-modulation of thermal stress, leading to near-surface tensile fracture, melt-related rock motion, and wind as the main mechanisms. Debris dampens the diurnal amplitude of the temperature and thus protects the ice from a cyclic mechanical damage, which cracks exposed ice most intensively early in the morning. Together with a well-known thermal insulation effect of debris, such property should protect weathering crust of glaciers from fast degradation.