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| Titel |
Micro-seismic precursory cracks prior to rock-fall on coastal chalk cliffs: a case study at Mesnil-Val, Normandie, NW France |
| VerfasserIn |
G. Senfaute, A. Duperret, J. A. Lawrence |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Science ; 9, no. 5 ; Nr. 9, no. 5 (2009-10-02), S.1625-1641 |
| Datensatznummer |
250006984
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| Publikation (Nr.) |
 copernicus.org/nhess-9-1625-2009.pdf |
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| Zusammenfassung |
| Erosion of rock cliffs has been considered to be relatively unpredictable.
This perceived stochastic nature of the erosional processes often occurs
through collapses along fractures in the rock-mass. The prediction of
catastrophic cliff failures and collapses remains very difficult. For
advancing in this field, it is important to understand the processes through
which a crack is initiated, how it develops and propagates until the final
failure. This paper examines the micro-seismic signals recorded 15 h
prior to a rock-fall located at Mesnil-Val, France. The results lead to the
hypothesis that several phases of failure mechanisms contribute to rock-fall
occurrence. The most important phases were associated with micro-seismic
event families identified by multiplet selection. Each event family
contained one specific frequency spectrum showing a progressive decrease of
the frequencies as the rock approached failure suggesting the following
phases: 1) the micro-seismic events recorded 15 h before the rock-fall
were characterised by the highest frequencies in a large spectrum-band,
between ~100 and 1000 Hz (family 1), suggesting a crack initiation
mechanism or the opening of existing fractures; 2) the micro-seismic events
recorded several minutes before the rock-fall were associated with a clear
decrease in the highest frequency components (family 2) suggesting that the
mechanism was related to the growing and development (or coalesce) of
existing micro-cracks into larger fractures; 3) micro-seismic events recorded
just before the rock-fall were associated with a lower frequency spectrum
than families 1 and 2, the highest frequency components were absent (family 3),
the frequency emission source mechanism could be related to the shearing
or opening of the existing large fractures permitting the complete
detachment of the blocky rock-mass; 4) finally, micro-seismic events with a
very low frequency spectrum (lower than 100 Hz) characterized the rock-fall
impact on the ground. These encouraging results offer the possibility of
using the micro-seismic system to monitor high risk sections of coastline
and to advance understanding of cliff failure mechanisms. |
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