Characterizing granular flows using associated seismic signal
Gravitational flows (avalanches, rockfalls) represent a major hazard for population in mountainous, seismic and volcanic areas.
They are however very dangerous to observe on the field.
Recent studies showed that avalanches and rockfalls can be detected, localized and characterized (volume, duration) from their seismic signals.
They are however very dangerous to observe on the field.
Recent studies showed that avalanches and rockfalls can be detected, localized and characterized (volume, duration) from their seismic signals.
LABORATORY EXPERIMENTS (2012-2015)
OBJECTIVE: obtain scaling laws relating the flow characteristics to the seismic parameters that can be exported to field problems.
Two types of laboratory experiments have been conducted:
(1) Individual beads were dropped on different hard supports to investigate the influence of the bead's radius and fall height on the generated seismic signal characteristics (duration, amplitude, frequency content...).
Can we characterize a simple impact (mass, speed of the impactor) from the generated seismic signal ?
(2) Granular columns of steel beads were first held with a magnet and then released from rest onto a hard support.
What are the relations between the column's characteristics (volume, aspect ratio (height over length), beads diameter) and the seismic metrics (energy, frequencies) ?
Two types of laboratory experiments have been conducted:
(1) Individual beads were dropped on different hard supports to investigate the influence of the bead's radius and fall height on the generated seismic signal characteristics (duration, amplitude, frequency content...).
Can we characterize a simple impact (mass, speed of the impactor) from the generated seismic signal ?
(2) Granular columns of steel beads were first held with a magnet and then released from rest onto a hard support.
What are the relations between the column's characteristics (volume, aspect ratio (height over length), beads diameter) and the seismic metrics (energy, frequencies) ?
The following video shows a granular column collapse with its associated seismic signal. The different phases of the collapse (main column collapse and the following individual bead impacts and rolling) have a different temporal/frequency signature.
Play the video below to ear the acoustic signature of the collapse:
KEY REFERENCES
Farin, M., Mangeney, A., De Rosny, J., Toussaint, R., Sainte-Marie, J. and Shapiro, N. (2016). Experimental validation of theoretical methods to estimate the energy radiated by elastic waves during an impact. J. of Sound and Vib.
Farin, M., Mangeney, A., Toussaint, R., De Rosny, J., Shapiro, N., Dewez, T., Hibert, C. Mathon, C., Sedan, O., and Berger, F. (2015). Characterization of rockfalls from seismic signal: insights from laboratory experiments. J. of Geophys. Res.: Solid Earth.
Farin, M., Mangeney, A., De Rosny, J., Toussaint, R., Sainte-Marie, J. and Shapiro, N. (2016). Experimental validation of theoretical methods to estimate the energy radiated by elastic waves during an impact. J. of Sound and Vib.
Farin, M., Mangeney, A., Toussaint, R., De Rosny, J., Shapiro, N., Dewez, T., Hibert, C. Mathon, C., Sedan, O., and Berger, F. (2015). Characterization of rockfalls from seismic signal: insights from laboratory experiments. J. of Geophys. Res.: Solid Earth.
THEORETICAL MODEL AND FIELD WORK (2015-2017)
During my postdoc at Caltech, I developed a theoretical model for the high-frequency (> 1 Hz) seismic signal generated by block impacts in debris flows, a strongly agitated mixture of rocks and water propagating rapidly (1-10 m/s).
Example of debris flow:
Example of debris flow:
OBJECTIVE: Determine an expression for the seismic power generated by particle impacts at a given distance from a debris flow.
This require us to evaluate the rate of particle impact and the force per impact at the base of debris flows.
I also installed a monitoring system (camera, seismic stations, lasers,...) to measure the dynamics and the seismic signal of debris flows generated by rainfalls in the San Gabriel mountains, near Pasadena, CA.
Here is a documentary about a field campaign I participated in 2016 with people from the USGS to install seismic stations along the legendary USGS debris flow flume [Iverson, 1997].
KEY REFERENCES
Farin, M., Tsai, V.C., Lamb, M.P. and Allstadt, K. (in prep.). Towards a physical model of the high-frequency seismic signal generated by debris flows.