Two PhD positions in IPGP Paris : Experimental and numerical modelling of acoustic waves from granular flows
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(1) Experimental acoustic emissions from granular flows
Anne
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Anne Mangeney
Professeur Université Paris-Diderot
Responsable Equipe Sismologie
Institut de Physique du Globe de Paris
et Equipe ANGE INRIA - Jacques Louis Lions - CETMEF
1, rue Jussieu, 75238 Paris cedex 05, France
Tel : +33 183957562, Fax : +33 183957716
website : http://www.ipgp.fr/~mangeney/
Experimental study of acoustic emissions from granular flows
Advisors: MANGENEY Anne, PR, mangeney@xxxxxxx, DE ROSNY Julien, DR, julien.derosny@xxxxxxxx, TOUSSAINT Renaud, CR, renaud.toussaint@xxxxxxxxxx
Host lab/ Team : Institut de Physique du Globe de Paris- Seismology group – UMR7154
The seismic signal generated by rockfalls, landslides or avalanches provides a unique tool to detect, characterize and monitor gravitational flow activity, with strong implication in terms of natural hazards. Indeed, as natural flows travel down the slope, they apply stresses on top of the Earth surface, generating seismic waves in a wide frequency band, associated to the different physical processes involved. As an example, by coupling seismic and video recording of rockfalls on Réunion Island, Hibert et al. [2014] showed the existence of high frequencies generated by impacts of blocs and of low frequencies, associated with granular flows. However, the complexity of natural flows where several effects such as erosion, presence of fluid, complex topography, etc. are mixed up, makes it difficult to distinct between the processes involved and therefore to quantify their relative contribution.
The objective of this PhD is to address this problem by developing laboratory experiments dedicated to the measurement of acoustic waves generated by granular flows. Indeed, the new granular flow experiments that we have carried out in collaboration with Institut Langevin and IPGS show that piezoelectric transducers and accelerometers with an acquisition rate of several MHz, placed on the underlying elastic substrate below an avalanche, record a measurable signal, making it possible to monitor the propagation of seismic waves in the basement during the flow [Farin et al., 2013b]. These waves carry the signature of the source (size, volume, velocity, grain roughness, behavior of the flow, etc.). Using a combination of optical and acoustic methods, we will measure the seismic signal generated by granular flows on different substrates at the laboratory scale. These substrate will be made of plates and blocs of different sizes and characteristics. We will first study the seismic signals associated with the impact and rolling of beads of different properties before investigating the collapse of granular columns over horizontal and sloping substrates. The full waveforms will be recorded continuously using a 64 channels acoustic monitoring system and the source flow itself will be simultaneously imaged by a fast camera (1000 frames/s), synchronized with the acoustic monitoring system. In particular, we will try to identify the seismic wave phases, the characteristics and patterns of the full waveform, the energy partition, and how they depend on the flow properties that can be easily tuned experimentally.
Ultimately, these experiments will guide the recognition of seismic waves generated by selected natural landslides. In particular, we will analyze the impacts of rocks instrumented in Tahiti (collaboration BRGM) and recurrent rockfalls on the Piton de la Fournaise volcano, Réunion Island. These researches will be a basis for future development of operational methods for monitoring gravitational hazards in collaboration with the volcanic and seismic Observatories in la Réunion (OVPF) and Antilles (OVSM).
This PhD, funded by Europe, is part of a large European project ERC SLIDEQUAKES, involving a team of 6 young researchers in complementary domains (geophysics, physics, mechanics and mathematics). This research will be performed in the seismology team of IPGP among reasearchers interested in modelling and monitoring of environmental sources (gravitational flows, volcanoes, oceans, hurricans, glaciers, quarries, etc.). For more information on the research group: http://www.ipgp.fr/~mangeney/Research.html
For more information go to http://ed109.ipgp.fr, section: Offres de these ( PhD offer), You must apply on the Doctoral School website
Numerical modeling of landslides and generated seismic waves
Advisors: MANGENEY Anne, PR, mangeney@xxxxxxx, CAPDEVILLE Yann, CR (LPGN): yann.capdeville@xxxxxxxxxxxxxx
Host lab/ Team : Institut de Physique du Globe de Paris- Seismology group – UMR7154
The goal of the PhD project is to take a major step in improving the detection, prediction and understanding of landslides and their modeling at the field scale through the analysis of generated seismic waves. The seismic signal generated by landslides (i. e. landquakes) provides a unique tool to estimate the properties of the flow and its dynamics and mechanical behavior. Indeed, the fluctuation of the stress applied by the landslide to the ground, which generates seismic waves, is highly sensitive to the flow history and therefore to the physical properties during mass emplacement.
The strategy of the project including this PhD is to
combine a very accurate description of the landslide source, and the simulation
and measurements of landquakes from the laboratory to the natural scale, by
leading an interdisciplinary project involving numerical modeling and
observation. More specifically, during this PhD, the methodology will be to
simulate the seismic waves generated by landslides by coupling granular flow
models to state-of-the-art wave propagation models. An ambitious objective will
be to develop efficient coupling methods. On the other hand the PhD student
will analyze, simulate and invert natural landquakes making use of
underexploited high-quality seismic and geomorphological data, in particular on
volcanoes.
Recent studies have shown that the long
period seismic signal generated by landslides can be simulated numerically by
coupling landslide models with wave propagation codes (Favreau et al.,
2010, Moretti et al., 2012). The comparison of the simulated and recorded
low frequency seismic signal makes it possible to discriminate between
different landslide scenarios, to constrain the physical processes at work in
landslide dynamics, and even the rheological parameters involved (Brodsky et
al., 2003, Favreau et al., 2010, Moretti et al., 2012).
Furthermore, Hibert et al., 2011 showed that the broad-band seismic
energy radiated by landslides can be used to deduce the landslide volume.
However, improvement the methods making it possible to deduce landslide
properties from the generated seismic signal requires better understanding and
quantification of both the effect of Earth heterogeneity and topography on wave
propagation, and of the physical processes at work in landslides. The PhD
student will address these questions by using and developing numerical modeling of
landslides taking into account erosion/deposition processes and fluid/solid
interactions, and couple these models with a hierarchy of wave propagation
methods depending on the period range and source/station distances. The
sensitivity of the seismic signal to landslide characteristics, topography and
physical processes involved will be investigated.
These models will be compared to laboratory
experiments on seismic emission of granular flows performed in collaboration
with Institut Langevin and IPGS and with real seismic data, recorded in
particular on the Dolomieu Crater, Piton de la Fournaise, Réunion Island and on
the Soufrière Hills, Montserrat.
This work will be performed in collaboration with specialists in mathematics for landslide modelling (F. Bouchut, LAMA, Marne-la-Vallée; E. Fernandez-Nieto et G. Narbona-Reina, University Séville) and in seismology (J. P. Ampuero and H. Kanamori, CalTech, Pasadena, USA). This PhD, funded by Europe, is part of a large European project ERC SLIDEQUAKES, involving a team of 6 young researchers in complementary domains (geophysics, physics, mechanics and mathematics). This research will be performed in the seismology team of IPGP among researchers interested in modelling and monitoring of environmental sources (gravitational flows, volcanoes, oceans, hurricans, glaciers, quarries, etc.). For more information on the research group: http://www.ipgp.fr/~mangeney/Research.html
For more information go to http://ed109.ipgp.fr, section: Offres de these ( PhD offer), You must apply on the Doctoral School website
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