Seismic attenuation in Antarctic firn

Abstract. We estimate the P- and S-wave seismic attenuation in polar firn from spectral analysis of diving-wave first-breaks of three-component active-source seismic observations carried out in 2010 on the Whillans Ice Stream (WIS), a fast-flowing ice stream in West Antarctica. The resulting quality factors are then successfully modeled using a rock-physics theory of wave propagation which combines White's mesoscopic attenuation theory of interlayer flow with that of Biot/squirt flow. The first theory describes an equivalent viscoelastic medium of a stack of two thin alternating porous layers of thickness much larger than the pore size but smaller than the wavelength. On the other hand, in the so-called Biot/squirt-flow model, there are two loss mechanisms, namely the Biot global-flow one and local flow from fluid-filled micro-cracks (or grain contacts) to the pore space and back, where the former is dominant over the latter. The fluid saturating the pores is assumed to be fluidized snow, which is defined as a mixture of snow particles and air, like powder, having zero rigidity modulus.