Measuring Depth to Ice-Bonded Permafrost Using Surface Waves: Challenges and Recommendations from Field Measurements in Eagle Summit, Alaska

The depth to ice-bonded permafrost is a critical piece of information for engineering design in cold regions. The use of non-invasive methods allows depth measurements to be made more rapidly than using traditional invasive methods resulting in project savings. However, while non-invasive methods may be faster than invasive techniques, non-invasive techniques must be carefully analyzed to produce meaningful results. Here we present the analysis of a unique surface wave dataset acquired in August 2023 in Eagle Summit, Alaska. Measurements followed a dynamic data acquisition methodology that resulted in multichannel analysis of surface waves (MASW) data from arrays of different lengths (23 and 2.3 m) and waveforms associated with different surface waves (i.e., Rayleigh and Love) and particle motion directions (i.e., Rayleigh-vertical, Rayleigh-inline, and Love-crossline). The Eagle Summit site (65.4621N, 145.4349W) is of particular interest because of the challenges associated with the data acquisition and interpretation. These challenges include the presence of thick near-surface organic material, obfuscating near-field effects, and ambiguous multi-mode dispersion trends. Yet, despite these challenges, the authors were successful in characterizing the shear wave velocity (Vs) to a depth of 5 m and identifying the top of ice-bonded permafrost at approximately 0.45 m. The authors hope that by presenting this unique and challenging dataset to highlight key challenges and provide recommendations for performing seismic measurements at permafrost sites.