Abstract:
As part of the ONR sea-ice mechanics initiative (SIMI) experiments in the spring of 1994, arrays of high-resolution seismic sensors were deployed in areas of high seismicity identified by real-time processing of acoustic emission events recorded by a wide, horizontal aperture hydrophone array. A major episode detected by the surveillance array was a new major lead opening up 2 km north of the ice camp. Two seismic arrays, each consisting of five three-component geophones in an 80-m aperture pentagon, were deployed 400 m apart on the edge of the lead. One of the methods employed for analysis of these data was the 2-D horizontal wave-number estimation of the recorded time series using plane wave beamforming. This procedure determined the propagation directions of arrivals of different wave types along with their dispersion characteristics. This analysis revealed a large number of events, corresponding to ``edge waves'' propagating in opposite directions along the lead. The analysis revealed that these waves behaved differently from the edge waves of bending-gravitational nature, predicted theoretically in the literature. Also, the broadband nature of these waves is inconsistent with floe resonances. To explain the nature of these waves, a simplified elastic model has been developed for the lowest-order modes of a floating, semi-infinite plate. The characteristics of the edge waves and the comparison with the simplified model are discussed. [Research supported by ONR.]