Journal cover Journal topic
Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
Nat. Hazards Earth Syst. Sci., 17, 939-955, 2017
https://doi.org/10.5194/nhess-17-939-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
22 Jun 2017
Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland
Fabian Walter1,2, Arnaud Burtin3,4, Brian W. McArdell2, Niels Hovius3, Bianca Weder1, and Jens M. Turowski3 1Laboratory of Hydraulics, Hydrology and Glaciology, ETH Zurich, Zurich, 8093, Switzerland
2Swiss Federal Institute for Forest, Snow and Landscape Research WSL, 8903 Birmensdorf, Switzerland
3GFZ German Research Centre for Geosciences, 14473 Potsdam, Germany
4Institut de Physique Du Globe de Paris, 75238 Paris, France
Abstract. Heavy precipitation can mobilize tens to hundreds of thousands of cubic meters of sediment in steep Alpine torrents in a short time. The resulting debris flows (mixtures of water, sediment and boulders) move downstream with velocities of several meters per second and have a high destruction potential. Warning protocols for affected communities rely on raising awareness about the debris-flow threat, precipitation monitoring and rapid detection methods. The latter, in particular, is a challenge because debris-flow-prone torrents have their catchments in steep and inaccessible terrain, where instrumentation is difficult to install and maintain. Here we test amplitude source location (ASL) as a processing scheme for seismic network data for early warning purposes. We use debris-flow and noise seismograms from the Illgraben catchment, Switzerland, a torrent system which produces several debris-flow events per year. Automatic in situ detection is currently based on geophones mounted on concrete check dams and radar stage sensors suspended above the channel. The ASL approach has the advantage that it uses seismometers, which can be installed at more accessible locations where a stable connection to mobile phone networks is available for data communication. Our ASL processing uses time-averaged ground vibration amplitudes to estimate the location of the debris-flow front. Applied to continuous data streams, inversion of the seismic amplitude decay throughout the network is robust and efficient, requires no manual identification of seismic phase arrivals and eliminates the need for a local seismic velocity model. We apply the ASL technique to a small debris-flow event on 19 July 2011, which was captured with a temporary seismic monitoring network. The processing rapidly detects the debris-flow event half an hour before arrival at the outlet of the torrent and several minutes before detection by the in situ alarm system. An analysis of continuous seismic records furthermore indicates that detectability of Illgraben debris flows of this size is unaffected by changing environmental and anthropogenic seismic noise and that false detections can be greatly reduced with simple processing steps.

Citation: Walter, F., Burtin, A., McArdell, B. W., Hovius, N., Weder, B., and Turowski, J. M.: Testing seismic amplitude source location for fast debris-flow detection at Illgraben, Switzerland, Nat. Hazards Earth Syst. Sci., 17, 939-955, https://doi.org/10.5194/nhess-17-939-2017, 2017.
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Short summary
Debris flows are naturally occuring mass motion events, which mobilize loose material in steep Alpine torrents. The destructive potential of debris flows is well known and demands early warning. Here we apply the amplitude source location (ASL) method to seismic ground vibrations induced by a debris flow event in Switzerland. The method efficiently detects the initiation of the event and traces its front propagation down the torrent channel.
Debris flows are naturally occuring mass motion events, which mobilize loose material in steep...
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