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ICEQUAKES

ICEQUAKES. Mathieu Doucette EPSC 330 – Term Presentation. Glacial Earthquakes. What are they? EQ spatially related to glaciers Regions with low tectonism How are they different? Radiate less energy Duration is NOT proportional to 10 M/2 Where are they found?

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ICEQUAKES

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  1. ICEQUAKES Mathieu Doucette EPSC 330 – Term Presentation

  2. Glacial Earthquakes • What are they? • EQ spatially related to glaciers • Regions with low tectonism • How are they different? • Radiate less energy • Duration is NOT proportional to 10M/2 • Where are they found? • Areas of heavy glaciation: Alaska, Antarctica, Greenland

  3. Initial Detection • Ekström et al, 2003 • Produced algorithm for detection • Manipulation of seismic data, 1999-2001 • Located 7292 events • 42 glacial EQs

  4. How do they occur? • Two theories (Tsai et al, 2008) • Calving • Basal flow • Radiation patterns? • Double coupling vs. Centroid Single Force • Need to fit the parameters

  5. Model Constraints • Proximity to calving fronts; accelerating outlet glaciers • Mechanisms follow direction of flow • Magnitude range 4.6-5.0 • Most energy between 20-100 s • Events are seasonal • Amplitude usually characteristic for each glacier

  6. Model Parameters • Viscoelastic deformation of ice • Weakening of ice by fracturing • Basal shear • Unconstrained friction-like parameter • Calving styles • Partially grounded, not partially grounded, buoyant • Subglacial water pressures • Effect of till • All of these need to factor in = produce EQ with long period signal

  7. Movement of Ice • Massive movement through calving, basal-slip • Studying ice movement • GPS trackers • Outlet glaciers • Combination of both theories? • Tsai et al, 2008, « Possible Mechanisms for Glacial Earthquakes » • Most parameters have to be estimated, models are uncertain.

  8. GPS Tracking

  9. Seasonality • Glaciers are affected by temperature • More melt = More calving • Change in friction below glacier • Most occur April-December

  10. Climate Change • Melting of glaciers • Meltwater on base = higher water pressure • Crevassing and Calving increase • Increasing EQ from 2000-2005 in Greenland • More EQ

  11. Conclusion • Discovered in 2003 • Long period, 35-150 s • Greenland, Alaska, Antarctica • Basal flow and/or Calving • Models require too many parameters • Hard to analyze and study • Affected by season and climate

  12. References • Ekström, G., Nettles, M., Abers, G.A., ‘’Glacial Earthquakes’’, Science, Vol.302, 622 (2003) • Ekström, G., Nettles, M., Tsai, V.C., ‘’ Seasonality and Increasing Frequency of Greenland Glacial Earthquakes’’, Science, Vol. 311, 1756 (2006) • Ekström, G., Nettles, M., ‘’Glacial Earthquakes in Greenland and Antarctica’’, Annual Review of Earth and Planetary Sciences, Vol. 38, 467-491 (2010) • Tsai, V.C., Rice, J.R., Fahnestock, M. ‘’Possible mechanisms for glacial earthquakes’’, Journal of Geophysical Research, Vol. 113, F03014 (2008)

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