Thermally induced icequakes detected on blue ice areas of the East Antarctic ice sheet

Abstract

Over a year of seismic observations, ~5000 short duration icequakes were detected by a permanent broadband station installed at the Princess Elisabeth base, located ~180 km inland in eastern Dronning Maud Land, East-Antarctica. Icequake detection via seismic waveform pattern recognition indicates the presence of two dominating clusters of events, totalizing ~1500 icequakes. The corresponding icequake locations point towards two distinct zones of outcropping blue ice areas (BIAs) located respectively at 4 and 1 km from the seismic station, both on the leeward side of a nunatak protruding through the ice sheet. The temporal occurrence of these icequakes suggests a close genetic link with thermal contraction of ice caused by significant surface cooling controlled, in summer by variations in diurnal solar radiation and in winter by strong cooling during cold katabatic regimes. Further analysis demonstrates the dependence of these icequakes on the absolute surface temperature and on its temporal change. Besides providing information on the ice fracture mechanics and rheology, investigations of thermal icequakes may be regarded as a ground-based proxy for the monitoring of the thermal state of BIAs, and characterization of ice-sheet ablation zones.

Wind-induced seismic noise at the Princess Elisabeth Antarctica Station

“…The origin of the diurnal activity could come from thermal icequakes resulting from diurnal temperature difference as observed and studied at ELIS (Lombardi et al, 2019). On all stations but especially at ANT5 and ANT6, there is a greater diurnal activity during A4 and A5, which correlates from a sudden drop of temperature and a greater temperature difference between the daytime/night-time ( Figure 6).…”

“…There seems therefore to be a small under-correction of the wind effect on the noise, caused either by slightly stronger local winds, or a slightly steeper relationship between wind and noise caused by coupling or installation settings. Stronger continuous cryoseismic activity could also explain the observations but based on Lombardi et al (2019) we would expect to see more diurnal variation if this activity was thermally induced.…”

“…In addition to the activity spanning over several days, the six stations show a strong diurnal activity which has been shown to be linked to temperature variation that induces thermal icequakes (Lombardi et al, 2019). Its intensity is larger at ANT6 throughout the deployment period.…”

“…We applied a similar model to each station of the temporary seismic network (ANT). Finally, we used these models to evaluate the impact of the wind-noise on the detectability of icequakes The seismic data at the PE comes from the broadband seismic station (ELIB) installed in February 2012 (Camelbeeck et al, 2019;Lombardi et al, 2019). This station worked irregularly up to the end of 2016 due to difficulties 100 providing continuous power supply during the austral winter, but recordings are continuous for the years 2017, 2018, and partly 2019 and 2020.…”

Continuous monitoring of the 2015–2018 Nevado del Ruiz activity, Colombia, using satellite infrared images and local infrasound records

“…There are multiple proposed mechanisms that cause icequakes especially on volcanoes covered by icecap, which include ice falling, ice surface cracking, resonant water-filled ice cavities, sudden changes in water flow rate (St. Lawrence and Qamar 1979;Métaxian 2003), stick-slip sliding (Allstadt and Malone 2014), and crevasse (Neave and Savage 1970). On the other hand, icequakes on volcanoes can be triggered by volcanic activity (Delgado et al 2015) and/ or thermal stress (Lombardi et al 2019). The icequakes induced by thermal stress happen when the air temperature decreases during clear nights (no clouds).…”