ICEQUAKES
Mathieu DoucetteEPSC 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 10M/2
• Where are they found?– Areas of heavy glaciation: Alaska, Antarctica,
Greenland
Initial Detection• Ekström et al, 2003• Produced algorithm for detection• Manipulation of seismic data, 1999-2001• Located 7292 events• 42 glacial EQs
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
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
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
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.
GPS Tracking
Seasonality
• Glaciers are affected by temperature• More melt = More calving• Change in friction below glacier• Most occur April-December
Climate Change
• Melting of glaciers• Meltwater on base = higher water pressure• Crevassing and Calving increase• Increasing EQ from 2000-2005 in Greenland• More EQ
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
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)
