Observation and inversion of seismo-acoustic waves in a complex arctic ice environment

Abstract

The propagation of low-frequency seismoacoustic waves in the arctic ice canopy is examined through the analysis of data collected during the 1987 PRUDEX ice camp. Study of the geophone time series generated by under-ice detonations reveals not only the expected longitudinal and flexural waves in the ice plate, but also unexpected horizontally polarized transverse (SH) waves. The travel paths of all three wave types are found to be refracted in the horizontal plane along a known ridge line locally separating the ice canopy into two distinct half-plates of thin first-year ice and thicker multi-year ice. The need to determine both the origin of the SH wave and location of each detonation from the received time series highlights the dramatic superiority of geophones over hydrophones in this aplication. Inversion of the geophone data for the ice sheet’s low-frequency elastic parameters is conducted initially by modeling the ice as a single homogeneous isotropic plate using SAFARI. A modified stationary phase approach is then used to extend SAFARI modeling to invert for the parameters of the two ice half-plates simultaneously. The estimated compressional/shear bulk wave speeds are comparable to previously obtained values; however, the compression/shear attenuation values are up to four times greater than earlier estimates.