Ultra high-resolution seismic imaging of permafrost, Devon Island, Nunavut
Carlos E. Nieto, Robert R. Stewart
In July-August, 2002, several shallow multicomponent seismic surveys and ground-penetrating radar traverses were conducted near the NASA Haughton-Mars Project camp on Devon Island, Nunavut. Geophones and hammer impacts in three different orientations (vertical, horizontal inline, and horizontal transverse) with different acquisition parameters were acquired successfully. Two different locations were selected to conduct seismic surveying, the Von Braun Valley and the Gemini Hills. The analysis of the ultra-high resolution seismic lines allowed the characterization of the saturated silt layer (top layer).
A compressional velocity of 260 m/s and a shear velocity of 168 m/s were obtained from the first break arrival times. We observe that the direct compressional wave changes its polarity with offset sign and with hammer impact orientation. The direct shear wave does not change polarity with the offset sign but it does with the hammer impact orientation. A more complex situation occurs with the head wave arrival. An estimated velocity of 3050 m/s was obtained from first break arrival times for a pure compressional head wave. Its polarity remains unchanged with offset. Variation of the velocity suggests layering in or over the permafrost, and lateral changes. What appears to be shear wave refraction was identified on the horizontal elements. An average velocity of 2250 m/s was obtained from first break arrival times. It was found that the polarity of this event changes with offset sign.