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| Titel |
Early Warning at the Gradenbach Mass Movement |
| VerfasserIn |
Werner Lienhart, Erich Lang, Stefan Mertl, Ulrike Stary, Ewald Brückl |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250076648
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| Zusammenfassung |
| The Gradenbach mass movement (GMM) is an example of a deep seated gravitational slope
deformation in the crystalline rocks of the Eastern Alps (12.85Ë E, 47.00Ë N). The main body
of the GMM covers an area of 1.7km2 and comprises a volume of 0.12km3. The main scarp is
located below the mountain crest at an elevation of 2235m. The toe is at 1200m elevation in
the Gradenbach valley. The GMM became active during the second half of the 19th
century according to historic documents. Quantitative data about the movement
are available since 1962. Quasi-stationary phases of creep or slow sliding were
interrupted by accelerations in 1965-1966, 1975, 2001, and 2009 yielding a total
displacement of about 20m. The cumulative displacement during the high velocity phases
was about 8m in 1965/66 and about 1m in 2001 and 2009. A transition to rapid
and catastrophic sliding cannot be excluded during the acceleration phases in the
future.
The early warning system of the Gradenbach Observatory at the GMM consists of a
geodetic, a hydro-meteorological, and a seismological component. The geodetic component
comprises a GPS network with stations distributed over the whole GMM and two
wire-extensometers recording the displacement at the toe of the landslide relative to the
opposite slope. The GPS data are available in real time. The extensometer data are currently
transmitted in weekly intervals. The hydro-meteorological component comprises the real time
registration and data transmission of precipitation and temperature at one station on the
GMM. The water equivalent of the snow cover is weekly determined at 15 profiles. Snow
melt and infiltration into the GMM are estimated from this data. The hydrostatic water level is
measured at two borehole gauges. A proxy of the hydrostatic water level at the
surface of rupture is derived from the hydro-meteorological data and related to the
velocity of the GMM by a power law. Investigations show that a variation of the
hydrostatic water level at the surface of rupture is delayed to the actual input of
precipitation and snow melt. The velocity of the GMM can therefore be predicted more
than one month in advance. The seismological component at the GMM is based on
measurements of the seismic activity with a local seismic monitoring network with near
real time data transmission. The acceleration phase in 2009 was preceded by an
increase of the ambient noise and the occurrence of micro-earthquakes which also
continued during the acceleration phase. The noise analysis can be supplied in near real
time.
The backbone of the early warning system at GMM is the geodetic component. However,
the hydro-meteorological prediction and the seismic precursors enhance the preparedness and
allow for a better judgement of an incipient acceleration. So far the early warning
system is based only on the experiences from a relatively short monitoring period.
Continued monitoring will further improve its performance and reliability in the future. |
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