Constraining the Structure of Ross Ice Shelf by Spectral Autocorrelogram of Teleseismic P-wave Coda

The recent deployment of a broadband seismic array on the floating ice shelf in the Antarctica's Ross Sea, presents a great opportunity to study the shelf structure using broadband seismic data (Bromirski et al., 2015) . Previously, we demonstrated how temporal P-wave coda autocorrelation can be efficiently used to characterize properties of the grounded ice cap in Antarctica. In this study, we employ a further improvement of the P-wave coda autocorrelation method in order to decipher the ice-shelf structures, i.e., the thickness of the overlaying ice and water beneath. Generally speaking, autocorrelation method refers to a class of seismological methods utilizing single-component seismograms, which can either be continuous noise records or earthquake-related segments. Here, instead of ambient noise, we advocate the use of P-wave coda, the seismic record immediately following the P-wave arrival from teleseismic earthquakes, because it offers signals with relatively high frequency-content and steep illumination of subsurface structures. Particularly, we construct the autocorrelation stacks of P-wave coda in the spectral domain, which are equivalent via a Fourier transform to autocorrelograms in the time domain, widely being used in seismological literature. At some stations, the spectral autocorrelations exhibit prominent resonant peaks, which are associated with ice-water configuration of the ice shelf. Consequently, we present an inversion scheme to estimate ice- and water-thickness beneath some pilot stations. In our knowledge, our results are among the first measurements of this type made from seismic data. The measurements are self-consistent among neighboring stations. However, there is a significant discrepancy between these measurements and regularly-gridded models of ice and water thickness in Antarctica. Thus, the method has a great potential to complement the existing ice-shelf model and in future monitoring applications of the ice shelves.

Bromirski, P. D., Diez, A., Gerstoft, P., Stephen, R. A., Bolmer, T., Wiens, D. A., et al. (2015). Ross ice shelf vibrations. Geophysical Research Letters, 42(18), 7589-7597. https://doi.org/10.1002/2015GL065284