Ice Properties Derived from Reflection Seismics at a Cold Alpine Saddle and a Local Antarctic Dome
Creators: name: Diez, Anja
Publisher: name: Karlsruhe
Year: 2010

description: For paleoclimate reconstructions or to predict future changes in sea level rise the dynamics of ice need to be known. This knowledge can be gained by a better understanding about the physical properties of ice. To derive these ice properties reflection seismics can be carried out. Up to now it is not very common to investigate internal structures of glaciers with the help of seismic measurements. 
For this purpose data from Colle Gnifetti, Monte Rosa, Switzerland and Halvfarryggen, Dronning Maud land, Antarctica were analyzed. Colle Gnifetti, an alpine saddle, resembles very well polar ice conditions and is thus an excellent test area close by. The shallow glacier (60 m) and the thick firn pack (30 m) made it impossible to filter out internal reflections. Further Problems during filtering occurred due to parasitic resonances of the geophone. Nevertheless the diving wave could be used to derive a density profile of the firn and ice. At Halvfarryggen, a local dome of 900 m thickness, internal reflections could clearly be observed below the firn transition zone down to the bed. It was the first time that internal reflections could be observed at an ice dome. The changes in seismic velocity, which caused the reflections, could then be linked to changes in crystal orientation fabric (COF) by the analysis of the reflection coeficient and partly by an amplitude versus angle (AVA) analysis. The results thus support ice-dynamic modeling studies which indicate the presence of strongly oriented crystal fabric and their changes over depth.For paleoclimate reconstructions or to predict future changes in sea level rise the dynamics of ice need to be known. This knowledge can be gained by a better understanding about the physical properties of ice. To derive these ice properties reflection seismics can be carried out. Up to now it is not very common to investigate internal structures of glaciers with the help of seismic measurements. For this purpose data from Colle Gnifetti, Monte Rosa, Switzerland and Halvfarryggen, Dronning Maud land, Antarctica were analyzed. Colle Gnifetti, an alpine saddle, resembles very well polar ice conditions and is thus an excellent test area close by. The shallow glacier (60 m) and the thick firn pack (30 m) made it impossible to filter out internal reflections. Further problems during filtering occurred due to parasitic resonances of the geophone. Nevertheless the diving wave could be used to derive a density profile of the firn and ice.
At Halvfarryggen, a local dome of 900 m thickness, internal reflections could clearly be observed below the firn transition zone down to the bed. It was the first time that internal reflections could be observed at an ice dome. The changes in seismic velocity, which caused the reflections, could then be linked to changes in crystal orientation fabric (COF) by the analysis of the reflection coeficient and partly by an amplitude versus angle (AVA) analysis. The results thus support ice-dynamic modeling studies which indicate the presence of strongly oriented crystal fabric and their changes over depth.