13/07/2021

Geophysical characterization using optical fiber measurements


  • ORGANISATION/COMPANY
    University Cote d Azur and CEA Bruyères-le-Châtel
  • RESEARCH FIELD
    GeosciencesOther
    PhysicsAcoustics
  • RESEARCHER PROFILE
    First Stage Researcher (R1)
  • APPLICATION DEADLINE
    31/01/2022 23:00 - Europe/Brussels
  • LOCATION
    France › Valbonne
  • TYPE OF CONTRACT
    Temporary
  • JOB STATUS
    Full-time
  • HOURS PER WEEK
    35
  • OFFER STARTING DATE
    31/01/2022

OFFER DESCRIPTION

Optical fiber measurements have proven to be useful to assess geophysical near-surface parameters and to detect seismological events in newly accessible regions (cities, ocean floor, highways...) by leveraging the existing fiber-optic infrastructure. In particular, laser interferometry performed with DAS systems (Distributed Acoustic Sensing) allows measuring the cable axial strain related to passing seismo-acoustic waves, at any point along the cable and over tens of kilometers of cable.

The goal of this Ph.D. project is to further develop and quantify the potential of DAS technology for geophysical characterization of the shallow subsurface.

The first part of the Ph.D. will be dedicated to the evaluation of optical fiber measurements to provide a high-quality assessment of near-surface geophysical parameters (i.e. geological layers imaging and shear wave velocities). These data are of primary interest to evaluate local site effects for seismic hazard assessment, detect potential blind faults, allow temporal monitoring with fiber cables left in place. A first acquisition site will be the area surrounding the Rouvière fault, responsible for the 2019 Le Teil earthquake (Ardeche, France). This earthquake, characterized by a moment magnitude of 4.9 and a local magnitude of 5.4, is the largest earthquake to have occurred in metropolitan France for 16 years. The data acquired during the Ph.D. will provide valuable information on the fault geometry at depth. A second acquisition site will be in a CEA center which has been previously characterized with standard geophysical methods. In both cases, the goal will be to invert the geometry of the geological layers, to identify and characterize the presence of faults, and to invert the geophysical parameters of interest for seismic hazard assessment, such as shear wave velocity.

The second part of the Ph.D. concerns the ability of optical fiber measurements to characterize seismological sources and the associated elastic wave field. The main goal will be to extract the physical parameters of seismic wave propagation along a branch of optical fiber for comparison with traditional and calibrated seismic sensors. An active seismic experiment (PREMISE2) was recently carried out in southeastern France in an underground laboratory, the LSBB tunnel (Laboratoire Sous-terrain Bas Bruit, https://lsbb.cnrs.fr/), in 2020. Multiple active shots were recorded both with a 4 km long underground optical fiber and with traditional seismic sensors. Different optical fiber cables and different coupling methodologies were tested along the 4 km optical fiber. Furthermore, using a pre-installed vertical fiber the Ph.D. student will be able to work on a 500 m aperture 3D optical fiber sensor.

The Ph.D. is a joint program between the geophysical division of CEA in Paris region and the Geoazur lab of University Côte d’Azur, in the south of France. The candidate will spend the working time shared between the two institutions. She/he will be part of a broader group working on optical fiber measurements in Geoazur (Ph.D. students, Post-doctoral and senior researchers). This Ph.D. includes some fieldwork for the geophysical acquisition campaigns in the pilot sites The data of the PREMISE2 experiment are already acquired. Conferences fees, visits to the different institutions, and fieldwork costs will be supported by the CEA.

 

 

More Information

Selection process

Please send your letter, cv, and contact information of up to 3 referees to Amaury Vallage.

Offer Requirements

  • REQUIRED EDUCATION LEVEL
    Geosciences: Master Degree or equivalent
    Physics: Master Degree or equivalent
  • REQUIRED LANGUAGES
    ENGLISH: Good

Skills/Qualifications

Graduated students in Geophysics, Earth Sciences and/or Physics.

Specific Requirements

Strong skills in signal processing are necessary, and in seismic and/or acoustic propagation preferred. Hands-on experience in programming is also requied. For this project, the student will most likely work with Python and/or Matlab.

Work location(s)
1 position(s) available at
University Cote d'Azur and CEA Bruyères-le-Châtel
France
Valbonne
06600
250 avenue Albert Einstein
1 position(s) available at
CEA
France
Bruyères-le-Châtel

EURAXESS offer ID: 663622

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