Marine seismic refraction measurements of near-shore subsea permafrost

Marine permafrost studies have been conducted near shore in Prudhoe Bay, Alaska. Sound velocities, measured in the ocean sediments were used to determine the location of frozen materials. Velocities above 2500 m/s were judged to indicate frozen materials while lesser velocities were associated with non-frozen materials. A study area 1 km by 0.5 km was established, in waters ranging from 0.4 to 3 m deep near shore. Over 100 velocity measurements were made in the area. These measurements show a broad variation in frozen material velocities and a definite trend toward lower velocities with increasing distance from shore. Velocities near 4000 m/s were typically found within a few hundred metres from shore while at 1 km from shore the frozen material velocities were approximately 3000 m/s. No significant variation in frozen material velocities was observed in the direction parallel to the shore-line. The depth to the top of the frozen materials was found to vary widely over the study area suggesting a highly irregular and discontinuous material with little or no continuity to its upper surface. Typical depths to high velocity refractors ranged from about 5 m within 100 m of shore to about 25 m at 1 km from shore.