Identification of active release planes using ground-based differential InSAR at the Randa rock slope instability, Switzerland 1Geological Institute, Swiss Federal Institute of Technology (ETH), Zürich, Switzerland
2Federal Office for the Environment (FEON), Bern, Switzerland
*now at: Federal Agency for Nuclear Control (FANC), Brussels, Belgium
Received: 10 September 2009 – Accepted: 10 November 2009 – Published: 04 December 2009Abstract. Five ground-based differential interferometric synthetic aperture radar
(GB-DInSAR) surveys were conducted between 2005 and 2007 at the rock slope
instability at Randa, Switzerland. Resultant displacement maps revealed, for
the first time, the presence of an active basal rupture zone and a lateral
release surface daylighting on the exposed 1991 failure scarp. Structures
correlated with the boundaries of interferometric displacement domains were
confirmed using a helicopter-based LiDAR DTM and oblique aerial photography.
Former investigations at the site failed to conclusively detect these active
release surfaces essential for kinematic and hazard analysis of the
instability, although their existence had been hypothesized. The
determination of the basal and lateral release planes also allowed a more
accurate estimate of the currently unstable volume of 5.7±1.5 million m3.
The displacement patterns reveal that two different kinematic
behaviors dominate the instability, i.e. toppling above 2200 m and
translational failure below. In the toppling part of the instability the
areas with the highest GB-DInSAR displacements correspond to areas of
enhanced micro-seismic activity. The observation of only few strongly active
discontinuities daylighting on the 1991 failure surface points to a rather
uniform movement in the lower portion of the instability, while most of the
slip occurs along the basal rupture plane. Comparison of GB-DInSAR
displacements with mapped discontinuities revealed correlations between
displacement patterns and active structures, although spatial offsets occur
as a result of the effective resolution of GB-DInSAR. Similarly, comparisons
with measurements from total station surveys generally showed good
agreement. Discrepancies arose in several cases due to local movement of
blocks, the size of which could not be resolved using GB-DInSAR.
Citation: Gischig, V., Loew, S., Kos, A., Moore, J. R., Raetzo, H., and Lemy, F.: Identification of active release planes using ground-based differential InSAR at the Randa rock slope instability, Switzerland, Nat. Hazards Earth Syst. Sci., 9, 2027-2038, doi:10.5194/nhess-9-2027-2009, 2009.