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- Title
Analysis of large rock slope instabilities using frequency domain decomposition modal analysis.
- Authors
Häusler, Mauro; Michel, Clotaire; Burjánek, Jan; Fäh, Donat
- Abstract
Seismic ambient vibrations are increasingly used to investigate the stability of rock columnsand unstable mountain slopes. The seismic wavefield amplification and polarization within anunstable rock mass can be compared to a stable reference outside the instability and canprovide a rapid estimate of its extent and geometry. Especially low-activity landslidesshow small surface displacements, so that geodetic and radar based techniques areunable to detect unstable volumes within a reasonably short time. Here, ambientvibrations provide a promising alternative. In addition, recording ambient vibrationsis of great importance when assessing the response of the site to an earthquake,potentially leading to coseismic slope failure. On slopes exhibiting deep cracksseparating the instability into individual subvolumes, seismic normal modes can beobserved, representing standing waves trapped in different compartments of theinstability. We performed an operational modal analysis using the Frequency DomainDecomposition (FDD) technique on ambient vibration data acquired with a temporary arrayconsisting of twelve 5s seismometers and two permanently installed short-period 1sseismometers on a large unstable rock slope near Preonzo in southern Switzerland(>150’000 m3). We compare the normal mode shapes based on FDD to results fromwavefield polarization analysis and site-to-reference spectral ratios (SRSR) anddemonstrate that FDD is a suitable tool to analyse and monitor large landslides. Especiallythe capability of FDD to identify higher and close modes are significant benefitscompared to simpler techniques such as SRSR or picking peaks on power spectra.Furthermore, the enhanced FDD provides an estimate of the damping of the modesthat could be a critical parameter related to the geometry of the unstable slope.
- Subjects
SWITZERLAND; ROCK slopes; ROCK analysis; MODAL analysis; MODE shapes; STANDING waves; OPERATIONS research; EFFECT of earthquakes on buildings; SATELLITE geodesy
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article