The influence of pressure ridges on seismic signals due to thermal cracking of sea ice

Thermal stress can fracture sea ice resulting in the radiation of both acoustic energy into the water and seismic waves in the ice. However, the distribution of seismic energy is strongly modified by the presence of pressure ridges which attenuate flexural waves. Observations of thermal stress cracks with an array of geophones and hydrophones on land‐fast first‐year ice provide an opportunity for evaluating this effect. The acoustic measurements allow precise positioning of individual fractures and the geophones allow measurement of the seismic signals. Few of the events occurring behind a pressure ridge result in detection of significant flexural wave energy, whereas most sources at equivalent range without an intervening pressure ridge have strong seismic signals. Attenuation by the ridge is explained with a flexural model of a plate which also includes a change in thickness and porosity representing the pressure ridge.