Vibroseismics in Glaciology

• Main Author: Eisen, Olaf
• Format: Conference Object
• Language: unknown
• Published: 2011
• Subjects: Antarc*; Antarctica
• Online Access: https://epic.awi.de/id/eprint/23597/; https://hdl.handle.net/10013/epic.36504

Reflection seismics has traditionally played an important part in glaciology since the 1920s. Mostly, explosive seismic source were utilized. One disadvantage is that they have to be deployed in boreholes, which cannot used repeatedly because of destruction by the charge. Moreover, the source signal is very variable and cannot be retrieved for processing purposes. Application of active reflection seismics in Antarctica and on the cold, firn-covered Alpine saddle Colle Gnifetti using seismic vibrators as sources indicate that the vibroseismic technique has several advantages to overcome current shortcomings of explosive seismic sources. Most noteworthy advantages of vibrators are their operation from the surface and the basically destruction-free application, allowing for numerous repeated shots at the same position without signal degradation.The results presented here show that the application of vibroseis in glaciology enables us to detect internal layers, likely caused by changing crystal orientation fabric, determine properties of the ice-bed interface, and image the rock and sediments underneath an ice mass. Our utilized vibrators basically represent the end-members of available devices, from an industrial standard with a peak force of 120 kN in a frequency range of 10-100 Hz to microvibrators with only some 100 N, with a pressure- (30-180 Hz) and a shear-wave (60-360 Hz) version. Comparison of microvibrator data acquired on the firn-covered Alpine saddle Colle Gnifetti with those from non-ice covered surfaces as well as small explosive sources indicate that the data are of very high quality. This is not only attributed to the small employed forces, which keep the structure of the surface firn intact, but to the complete transmission path, yielding a total p-wave penetration depth of some 150 m into bedrock underneath the 60 m thick glacier.