An Assessment of Crustal and Upper­Mantle Velocity Structure by Removing the Effect of an Ice Layer on the P­Wave Response: An Application to Antarctic Seismic Studies

Abstract

Standard P-wave receiver function analyses in polar environments can be difficult because reverberations in thick ice coverage often mask important P-to-S con- versions from deeper subsurface structure and increase ambient noise levels, thereby significantly decreasing the signal-to-noise ratio of the data. In this study, we present an alternative approach to image the subsurface structure beneath ice sheets. We utilize downward continuation and wavefield decomposition of the P-wave response to obtain the up- and downgoing P and S wavefield potentials, which removes the effects of the ice sheet. The upgoing P wavefield, computed from decomposition of the waveform at a reference depth, is capable of indicating ice layer thickness. This simple step removes the necessity of modeling ice layer effects during iterative inversions and hastens the overall velocity analysis needed for downward continuation. The upgoing S wave is employed and modeled using standard inversion techniques as is done with receiver functions at the free surface using a least-squares approximation. To illustrate our proof of concept, data from several Antarctic networks are examined, and our results are com- pared with those from previous investigations using P- and S-wave receiver functions as well as body- and surface-wave tomographic analyses. We demonstrate how our ap- proach satisfactorily removes the ice layer, thus creating a dataset that can be modeled for crustal and upper-mantle structure. Solution models indicate crustal thicknesses as well as average crustal and upper-mantle shear-wave velocities.