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Barruol, G., Cordier, E., Bascou, J., Fontaine, F. R., Legrésy, B., Lescarmontier, L. |
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Tide-modulated Icequakes in the Mertz Glacier Grounding Area, East Antarctica |
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Conference - International - Communication |
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2013 |
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We deployed a seismic network along the Adélie and George V coasts in East Antarctica during the period 2009-2012. This allowed us to monitor the cryo-seismic activity of coastal glaciers and to get new insights on the relationship between tidal cycles and ice-stream flows. Systematic icequake detection was performed and reveals a large micro-seismicity at seismometers installed close to floating ice tongues and particularly at a seismic sensor located on the bedrock in the vicinity of the grounding area of the 35 km-broad Mertz glacier, a major outflow of this region, flowing at more than 3 m/day. We detected a large microseismicity (50,000 events detected within 10 months and up to 100 events/hour) characterized by short duration (<2 s), impulsive waveforms and by a rich frequency content between 1 and 20 Hz. The microseismicity was compared with the sea level variation calculated from the regional TUGO tide model validated with 7 regional tide observations. We demonstrated a clear tidal modulation of the icequakes with dominant semi-diurnal, diurnal and fortnightly variations. Each diurnal tidal cycle is related to two icequake activity peaks: a first peak occurs at mid-rising tide and a second peak of much larger amplitude occurs at mid–falling tide, both corresponding to the maximum of sea-level velocity variation. On a two-weeks cycle, the maximum number of icequakes generally coincides with spring tides whereas neap tides do not generate any significant number of icequakes. We propose that the observed icequake activity close to the Mertz grounding area reflects ice (micro) fracturation induced by the friction of the glacier flowing around the rocky outcrop, but also the accommodation of the bending of the ice slab during the falling and rising tides around the outcrop where the seismometer was installed, close in the grounding zone. |
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yes |
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4773 |
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