Sea Ice Thickness and Elastic Properties From the Analysis of Multimodal Guided Wave Propagation Measured With a Passive Seismic Array

Abstract

Field data are needed for a better understanding of sea ice decline in the context of climate change. The rapid technological and methodological advances of the last decade have led to a reconsideration of seismic methods in this matter. In particular, passive seismology has filled an important gap by removing the need to use active sources. We present a seismic experiment where an array of 247 geophones was deployed on sea ice, in the Van Mijen fjord near Sveagruva (Svalbard). The array is a mix of 1C and 3C stations with sampling frequencies of 500 and 1000 Hz. They recorded continuously the ambient seismic field in sea ice between 28 February and 26 March 2019. Data also include active acquisitions on 1 and 26 March with a radar antenna, a shaker unit, impulsive sources, and artificial sources of seismic noise. This data set is of unprecedented quality regarding sea ice seismic monitoring, as it also includes thousands of microseismic events recorded each day. By combining passive seismology approaches with specific array processing methods, we demonstrate that the multimodal dispersion curves of sea ice can be calculated without an active source and then used to infer sea ice properties. We calculated an ice thickness, Young's modulus, and Poisson's ratio with values h = 54 ± 3 cm, E = 3.9 ± 0.15 GPa, and = 0.34 ± 0.02 on 1 March, and h = 58 ± 3 cm, E = 4.4 ± 0.15 GPa, and = 0.32 ± 0.02 on 5 March. These values are consistent with in situ field measurements and observations.

Accurate Estimations of Sea‐Ice Thickness and Elastic Properties From Seismic Noise Recorded With a Minimal Number of Geophones: From Thin Landfast Ice to Thick Pack Ice

“…This gives E = 3.8 GPa and ν = 0.35, which is consistent with the values reported in Moreau et al. (2020): E = 3.9 ± 0.2 GPa and ν = 0.34 ± 0.02, which were estimated from a frequency‐wavenumber analysis based on the recordings of 52 geophones. The density is set to 900 kg/m 3 , a common value for sea ice.…”

“…On March 24, the estimated thickness is 63 cm with a standard deviation of 2.7 cm in the PDF when using 5 stations, and 65 cm with a standard deviation of 3 cm in the PDF when using 3 stations. These values are consistent with those found when using active sources, as well as with estimations from the same icequakes when applying the method introduced in Moreau et al (2020), based on an inversion of the wavenumbers of the modes.…”

“…This was also observed in the field from ice drillings and ground penetrating radar acquisitions, which indicated an increase of 10-15 cm. Moreover, the thickness estimates are consistent with the values found when applying the method introduced in Moreau et al (2020). This method is based on a simultaneous inversion of the frequency-wavenumber spectrum of the QS, QS 0 , and SH 0 modes.…”

“…The data processed in this section were recorded in the Van Mijen fjord near Sveagruva, in Svalbard (Moreau et al., 2020). Figure 2a shows the location of the deployment in the fjord.…”

“…The method is first applied to thin landfast ice. Based on a very rich dataset recorded in 2019 in the Van Mijen fjord, in Svalbard (Moreau et al, 2020), we demonstrate its robustness, stability, and accuracy by processing waveforms from many active sources and from icequakes (Section 3.1). Then, the method is applied to icequakes recorded on thick pack ice in the Arctic ocean in 2007 (Gascard et al, 2008;Vihma et al, 2014), indicating ice thickness values that are consistent with in situ measurements and field observations (Section 3.2).…”