Japan Geoscience Union Meeting 2016

Presentation information

International Session (Oral)

Symbol M (Multidisciplinary and Interdisciplinary) » M-TT Technology & Techniques

[M-TT05] Cryoseismology - a new proxy for detecting surface environmental variations of the Earth -

Thu. May 26, 2016 1:45 PM - 3:15 PM 202 (2F)

Convener:*Masaki Kanao(National Institute of Polar Research), Seiji Tsuboi(JAMSTEC, Center for Earth Information Science and Technology), Takeo Ito(Earthquake and Volcano Research Center, Graduate School of Environmental Studies, Nagoya University), Douglas Wiens(Washington University in St Louis), Sridhar Anandakrishnan(Penn State University), Jeremy Winberry(Central Washington University), Kent Anderson(Incorporated Research Institutions for Seismology), Chair:Seiji Tsuboi(JAMSTEC, Center for Earth Information Science and Technology), Masaki Kanao(National Institute of Polar Research)

2:15 PM - 2:45 PM

[MTT05-07] Seismic-infrasound monitoring of a tidewater calving glacier (Bowdoin, Greenland)

★Invited papers

*Evgeny A. Podolskiy1, Shin Sugiyama2, Martin Funk3, Riccardo Genco4, Masahiro Minowa2, Fabian Walter3, Shun Tsutaki2,5, Maurizio Ripepe4 (1.Arctic Research Center, Hokkaido University, Sapporo, 2.Institute of Low Temperature Science, Hokkaido University, Sapporo, 3.Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zurich, Zurich, 4.Dipartimento di Scienze della Terra, Università di Firenze, Florence, 5.Arctic Environment Research Center, National Institute of Polar Research, Tokyo)

Keywords:Greenland, tidewater glacier, icequake, seismic, infrasound, calving

Greenland is the second largest ice-covered area worldwide, where recent dramatic recession of outlet glaciers is known to be a key driver for accelerated ice-sheet mass loss. Bowdoin Glacier in northwestern Greenland (~120 km from Thule) is a grounded tidewater calving glacier that has been rapidly retreating since 2008. An observational seismic-infrasound network was installed in July 2015 near the 3-km-wide calving front of the glacier to enable near-source monitoring of frontal dynamics.
One Güralp CMG40T triaxial broadband seismometer was installed on the rocky coast in advance of the calving front, together with a time-lapse camera and a water pressure sensor in the fjord (for recording micro-tsunamis generated by calving). Four Lennartz LE-3D short- and long-period seismometers were arranged on the glacier ice in a triangle-shaped array, ~250 m from the marginal ice cliff, where icebergs are discharged into the fjord. An infrasound array comprising four pressure sensors was installed on a hill located ~3 km behind the calving front. Another two infrasound sensors were collocated with the central station of the on-ice seismic array and the broadband station. The aperture of both arrays was ~150 m. Additionally, three GPS on-ice stations with an on-rock reference station were established along the longitudinal profile of the Bowdoin Glacier to record ice-flow speed. Finally, an automatic weather station was used to record meteorological parameters near a base camp east of the glacier.
Multiple seismic and infrasound events were recorded and linked to surface crevassing, calving, presumably hydrofracturing, iceberg rotations, teleseismic earthquakes, helicopter-induced tremors, etc. Using classic seismological and array approaches (i.e., “Short Term Averaging / Long Term Averaging” and “f-k” analysis), as well as image processing, we explore and inter-compare this unique dataset. The most striking feature of the records is the temporal variability of microseismic events, which were continuously recorded over a period of two-weeks. The results show a double-peak diurnal oscillation in the number of events (up to 600 events per hour). Using high-resolution surface displacement GPS measurements, we show that the correlation between the number of events and tides is relayed through strain-rate variation. The strain rate corresponds to local extensional stretching of the glacial surface, mainly in response to increases in air temperature and falling tide velocity, which reduces back-pressure on the ice cliff.