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Thesis on the development of an optical deformation sensor for geophysics and volcanology M/W

This offer is available in the following languages:
Français - Anglais

Date Limite Candidature : dimanche 17 juillet 2022

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General information

Reference : UMR5243-HELOUR-025
Workplace : MONTPELLIER
Date of publication : Monday, May 16, 2022
Scientific Responsible name : Jean Chery
Type of Contract : PhD Student contract / Thesis offer
Contract Period : 36 months
Start date of the thesis : 1 October 2022
Proportion of work : Full time
Remuneration : 2 135,00 € gross monthly

Description of the thesis topic

Since the 2000s, the development of geodetic observation networks (GNSS, InSAR, strainmeters) has made possible to document numerous slow slip events on faults, both in the subduction domain (Dragert et al. 2001; Ide et al. 2007) and on strike-slip faults (Murray and Segall, 2005). High-resolution borehole strainmeters have characteristics (Agnew 1986; Sakata 1981) that make them complementary to GNSS and InSAR measurements. In particular, they allow the observation of the three horizontal components of the deformation tensor (which includes six in total) with a resolution of the order of 1 nano-strain, thus detecting weaker movements than those detected by GPS/InSAR. However, they have a number of drawbacks that limit their use: high price, partial measurement of the deformation tensor, mechanical drift in the borehole. The project team has been building optical sensors for geophysics since 2009 (Seat et al. 2012, Chawah et al. 2015). We have been developing since 2020 at Geosciences and LAAS a 6-component borehole strainmeter prototype that should overcome these drawbacks. A first prototype should be installed in late 2022 or early 2023 on the Larzac hydro-geodetic observatory.
In this context, the PhD student will have a key role just after his arrival in the project. A first stay of 3 months at LAAS will allow him to participate to the optical calibration of the strainmeter with interferometric interrogation by optical fiber. Thereafter, the PhD student will evaluate the performance of the instrument in-situ by performing:
- the analysis of calibration data (in-situ overpressure) and the determination of a mechanical model of involving the strainmeter, the coupling material and the bedrock;
- the study of the adequacy between the 3D deformation tensor produced by the strainmeter and the predictions provided by the terrestrial tide models;
- interpretation and modeling of the transient deformation induced by hydrological phenomena occurring at the observation site, using complementary instrumental data (rainfall, piezometry, seismology, gravimetry, inclinometry) acquired at the Larzac Observatory (OSU OREME and H+ network).
These different elements of the research project will be published in the framework of the Geosciences Montpellier - LAAS INP collaboration.

Références :
Agnew, D. C. (1986). Strainmeters and tiltmeters. Reviews of Geophysics, 24(3), 579-624.
Chawah, P., J. Chery, F. Boudin, M. Cattoen, H.-C. Seat, G. Plantier, F. Lizion, A. Sourice, P. Bernard, C. Brunet, D. Boyer, S. Gaffet, A simple pendulum borehole tiltmeter based on a triaxial optical-fiber displacement sensor, Geophys. J. Int., 203, 1026–1038, 2015.
Dragert, H., Wang, K., & James, T. S. (2001). A silent slip event on the deeper Cascadia subduction interface. Science, 292(5521), 1525-1528.
Ide, S., Beroza, G. C., Shelly, D. R., & Uchide, T. (2007). A scaling law for slow earthquakes. Nature, 447 (7140), 76.
Sakata, S. (1981). On the concepts of some newly-invented borehole three-component strainmeters. Rep. Nat. Res. Center Disaster. Prev., 25, 95-126.
Seat, H.C. Chawah, P, Cattoen, M, Sourice, A, Plantier, G, Boudin, F, Chery, J, Brunet, C, Bernard, P, Suleiman, M, Dual-modulation fiber Fabry-Perot interferometer with double reflection for slowly-varying displacements, Optics letters, 37, 10.1364/OL.37.002886, 2012.

Work Context

The PhD student will be integrated in the Geosciences Montpellier laboratory, and will be affiliated to the GAIA graduate school (Biodiversity, Agriculture, Food, Environment, Land, Water). He will also spend time at the LAAS INP in Toulouse. The supervision team will be composed of Jean Chéry, Cédric Champollion and Michel Peyret (GM), as well as Han Cheng Seat, Michel Cattoen and Olivier Bernal (LAAS).
The PhD student will also collaborate with the ANR X-STRAIN 2022-2025 project team, in the framework of the installation of several strainmeters on the Haiyuan fault in China. This project is the subject of an academic collaboration with the Chinese Academy of Sciences.

Constraints and risks

Position specifics: Geographical mobility (national), including experimental research missions at LAAS Toulouse, and field work at the Larzac observatory (OSU OREME).

Additional Information

Expected Skills:
- Good knowledge in one or more of the following areas: geophysics, scientific instrumentation, optics, interferometric measurements, deformation mechanics, numerical modeling, signal processing, scientific programming;
- Writing skills for the production of scientific papers;
- Ability to work in a team;
- Autonomy and scientific curiosity;
- Critical thinking and synthesis.
Documents to be provided:
2 letters of recommendation to be attached to your cover letter

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