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 10 M/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

8. 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.

9. GPS Tracking

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

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

12. 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

13. 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)