Abstract :
[en] The presence of massive Quaternary loess units at the eastern border of the Fergana Basin
(Kyrgyzstan, Central Asia) makes this area particularly prone to the development of catastrophic
loess earthflows, causing damages and injuries almost every year. Efficient disaster
management requires a good understanding of the main causes of these mass movements, that
is, increased groundwater pressure and seismic shaking. This paper focuses on the Kainama
earthflow, mainly composed of loess, which occurred in 2004 April. Its high velocity and
the long run-out zone caused the destruction of 12 houses and the death of 33 people. In
summer 2005, a field survey consisting of geophysical and seismological measurements was
carried out along the adjacent slope. By combination and geostatistical analysis of these data,
a reliable 3-D model of the geometry and properties of the subsurface layers, as shown in
the first part of the paper, was created. The analysis of the seismological data allowed us to
point out a correlation between the thickness of the loess cover and the measured resonance
frequencies and associated amplification potential. The second part of this paper is focused
on the study of the seismic response of the slope by numerical simulations, using a 2-D finite
difference code named FLAC.Modelling of the seismic amplification potential along the slope
confirmed the results obtained from the seismological survey—strong amplifications at the
crest and bottom of the slope where there is a thick loess cover and almost no amplification in
the middle part of the slope. Furthermore, dynamic slope stability analyses were conducted to
assess the influence of local amplifications and increased groundwater pressures on the slope
failure. The results of the dynamic modelling, although preliminary, show that a combination
of seismic and hydrologic origin (pore pressure build-up during the seismic shaking) is the
most probable scenario responsible for the 2004 failure.
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