EGU2020-851
https://doi.org/10.5194/egusphere-egu2020-851
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Identifying icequakes at ice-covered volcanoes in Southern Chile

Oliver Lamb1, Jonathan Lees1, Luis Franco Marin2, Jonathan Lazo2,3, Andres Rivera4,5, Michael Shore1, and Stephen Lee6
Oliver Lamb et al.
  • 1Department of Geological Sciences, University of North Carolina at Chapel Hill, USA (olamb@email.unc.edu)
  • 2OVDAS-SERNAGEOMIN, Chilean Geological Survey, Chile
  • 3Department of Physical Sciences, University of La Frontera, Temuco, Chile
  • 4Centro de Estudios Cientificos, Valdivia, Chile
  • 5Departamento de Geografia, Universidad de Chile, Chile
  • 6US Army Research Laboratory/Army Research Office, Research Triangle Park, NC, USA

Volcanoes and glaciers are both productive sources of seismic activity which may be easily confused for each other, leading to potential missed warnings or false alarms. This presents a challenge for organizations monitoring active volcanoes with glaciers on or near the edifice. Cryogenic earthquakes (i.e. icequakes) have been studied at only a few volcanoes around the world and there is a ready need to develop robust methods for efficiently differentiating them from volcanic events. Here we present results from an ongoing study of icequakes at active ice-covered volcanoes in the Southern Chilean Volcanic Zone. The primary focus of the project so far has been on seismo-acoustic data collected at Llaima volcano, one of the largest and most active volcanoes in the region. The data, recorded in 2015 and 2019, was analysed using a combination of automatic multi-station event detection and waveform cross-correlation to find candidate repeating icequakes. We identified 11 persistent families of repeating events in 2015, and over 50 families in 2019; the largest family containing over 1000 events from January to April 2019. The persistent, repetitive nature of these events combined with their waveform characteristics and source locations suggest they originated from multiple sub-glacial sources on the upper flanks of the volcano. Low levels of volcanic activity at Llaima volcano since 2009 have allowed this clear discrimination of icequake events. We are also targeting Villarrica volcano in early 2020 with a network of seismo-acoustic sensors and to record icequake activity in concurrence with the ongoing eruptive activity at the summit. Altogether, the results from this project so far suggest icequakes may be more common than previously thought and has strong implications for how seismic data at ice-covered volcanoes may be interpreted.

How to cite: Lamb, O., Lees, J., Franco Marin, L., Lazo, J., Rivera, A., Shore, M., and Lee, S.: Identifying icequakes at ice-covered volcanoes in Southern Chile, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-851, https://doi.org/10.5194/egusphere-egu2020-851, 2019

Comments on the presentation

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Presentation version 1 – uploaded on 29 Apr 2020
  • CC1: Comment on EGU2020-851, Benjamin Lamb, 30 Apr 2020

    Great poster! Will your results need to be re-evaluated as glaciers ever rapidly recede?

    • AC1: Reply to CC1, Oliver Lamb, 01 May 2020

      That's a good question. There are a lot of different ways that receding glaciers can affect the icequake activity.

      We have evidence that some of the potential icequakes at Llaima volcano are coming from near the glacier terminus. It's certainly possible that the locations of these near-terminus icequakes will recede with the glaciers, or cease completely. It's also possible that icequakes located near the top of the glacier will stop as the glacier becomes thinner and slows down. Furthermore, the melting of the glaciers will change how meltwater reaches the base of the glacier where hydrological conditions can have strong effects on icequake activity. Lastly, the nature of the base beneath the glaciers (i.e. soft sediment or solid rock) can affect the prevalence of icequakes. If the receding glacier retreats across different basal geology, then the number of icequakes recorded might vary.

      Cheers!

  • CC2: Comment on EGU2020-851, Johanna Lehr, 07 May 2020

    Hi Oliver,

    I am wondering how exactly you want to distinguish between Ice-quakes and events related to volcanic activity. Do you do is solely by the source location? In that case you would need a very precise location, wouldn't you? At least if they occur close to potential volcanic source. Also, I am wondering why icequakes should be repetitive - maybe you can enlighten me.

    Best regards,

    Johanna

    • AC2: Reply to CC2, Oliver Lamb, 07 May 2020

      Hi Johanna, thanks for the great questions.

      It's pretty difficult to distinguish between volcanic and glacial by simply looking at frequency or waveform characteristics alone. Locations and depths of the source is definitely one of the key pieces of evidence for distinguishing seismicity so yes, we would need very good source locations. You can also look at the focal mechanisms (if possible) to see if shear failure has occured which might be related to slip along bottom of glacier. But this is still not easy to seperate from a source like slow-slip failure. Another line of evidence is to look at the rate of seismicity over time and see if there is any correlation with temperature, snow or rain variations. So, locations is definitely the most useful tool but there are other ways to get clues if accurate locations are not possible.

      Apologies for the confusion, but I don't think all icequakes are repetitive. The reason I look for repeating seismicity is that it is a common characteristic of icequakes that have been recorded at other ice-covered volcanoes such as Rainier and Katla. I believe it is also something seen in non-volcanic glacial regions such as Greenland, Antartica, and the Alps. I simply wanted to see if the same could be detected at Llaima volcano.