Revealing firn structure at Dome A region in East Antarctica using cultural seismic noise

Abstract. Antarctica is mostly covered by snow, firn, and glacier ice, and the transformation from snow to firn and glacier ice influences energy transfer and material transport in polar regions. In this paper, we deployed three linear seismic arrays near Dome A in East Antarctica during China's 39th Antarctic scientific expedition and used seismic ambient noise to reconstruct the firn structure nearby. The result shows that the ambient noise mainly comes from the Kunlun Station and is related to human activities. We resolved empirical Green's function that contains abundant multi-modal surface waves from 3 to 35 Hz, and reconstructed the shallow S-wave velocity, density, and radial anisotropy structures by inverting them. The reliability of the structure was validated by the ice-core data, which demonstrates the effectiveness of using cultural seismic noise for the reconstruction of shallow structures in Antarctica. The result shows that the S-wave velocity increases rapidly with a negative radial anisotropy (SH wave travels slower than SV wave) in the top 28 m, which corresponds to the transformation from snow to firn. The firn layer shows a fairly strong positive radial anisotropy (SH wave travels faster than SV wave) between 40 m and 70 m in depth, which corresponds to the recrystallization of firn. The radial anisotropy vanishes to zero at around 84 m in depth, denoting the transformation from firn to glacier ice. Overall, the multi-parameter results clearly show the transformation from snow to ice, and the internal evolution of firn at Dome A region. Furthermore, we compared several existing S-wave velocity profiles of firn structures in West and East Antarctica and found a relatively shallower transformation depth from firn to ice in West Antarctica, which indicates a faster accumulation rate of snow in West than in East Antarctica.