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The emergence of distributed optic fiber sensing has revolutionized the field of marine seismology enabling the transformation of submarine telecommunication cables into a dense array of receivers spaced every few meters over lengths of tens of kilometres. Dynamic strain rate measurements made by Distributed Acoustic Sensing (DAS) have shown to be sensitive to surface waves travelling longitudinally to fibers. Surface wave dispersion curves, extracted by spatial correlation of ambient seismic noise can then be used to determine a shear wave velocity model beneath the fibre optic cable lying on the seafloor. This PhD project aims to develop a novel seismic interferometry methodology optimised for DAS data to produce a shear-velocity tomographic image of an active fault. The project will use data acquired on a cable dedicated for scientific observations which traverses the strike-slip North Alfeo fault located off-shore Catania, Sicily. Results from the high-resolution passive imaging of this fault will be used in earthquake simulations to better understand the role damage zones play in earthquake physics of submarine strike-slip faults.

What will your mission be?

The emergence of the fiber sensing technique is an opportunity to increase our knowledge of offshore faults. The presence of a cable crossing the North Alfeo fault multiple times provides the opportunity to record the ambient noise wavefield with unprecedented spatial resolution by using the DAS technique across an active fault. Your aim during this project will be to optimize a seismic ambient noise processing technique, accounting for the nature of the DAS data in order to achieve a superior image of the subsurface compared to approaches that apply traditional seismological techniques. The first objective of this PhD project is to develop a complete workflow for the production of shear velocity tomography of an active fault area using fiber sensing. The second objective aims at interpreting this tomography for a better characterization and understanding of the North Alfeo strike-slip fault zone by creating a dynamic rupture model of the fault zone based on the tomographic results.

What will your activities be?

You will work on the analysis of DAS ambient noise seismic signals for improving imaging and physical characterization of the subseafloor.

• You will co-develop tools and skills in processing voluminous datasets taking advantage of Datarmor, Ifremer’s HPC facility.
• You will implement a workflow for high resolution surface wave inversion using DAS data with signal selection, data pre-conditioning as well as automatic picking for dispersion curves selections prior to inversion.
• You will implement inversion schemes taking into account 2D and 3D numerical modelling of surface waves propagation.
• You will work with the ALMA team on the interpretation of the inversion results in terms of the fault dynamics, testing the output model within a dynamic rupture model.

How to apply for this position?

Your application file must include:

• an academic transcript (Bachelor + Master 1 and first semester Master 2)

Your application must be compiled into 2 PDF files, up to 2 Mo for each file.

The deadline for applications is May 19th, 2025. Nevertheless, we strongly urge you to let us know as soon as possible of your intention to apply, by contacting the subject supervisor: STEPHAN KER

In parallel, please submit your application to the doctoral school: https://amethis.doctorat.org/amethis-client/

Doctoral students' contracts will start as of October 6th, 2025, subject to the submission of administrative documents authorizing Ifremer to recruit the doctoral student (certificate of completion of the Master 2 or engineering degree + visa for foreign doctoral students outside the EU).

What are the next steps?

• Assessment of CV, cover letter and reference letter
• Interview with the supervising team
• Interview with the University of Brest (UBO)

Who are you?

You have the following skills, knowledge and experience:

• Master 2 in geophysics or physics
• Good knowledge in modelling and signal processing
• Some prior experience in seismology/seismic interferometry is recommended

You have the following qualities:

• Particular interest in seismology and programming
• Rigour and curiosity

How are your activities organised?

• Data: two available DAS datasets acquired in November 2023 (10 days) and July 2024 (1 month) on the MEOC and FOCUS cables during the ERC project FOCUS
• Opportunity to acquire more DAS data in Eastern Sicily during the project
• Presentation of project’s results at national and international workshops/conferences
• Host institution infrastructures: Access to the HPC DATARMOR to perform large-scale data processing and inversion
• Rate of activity: 100%
• Position based at Ifremer, Plouzané
• Remote working (maximum of 8 days per month)

• Contrat: CDD - 3 ans

What are your benefits?

Benefits from the project

You will be part of an active research team focusing on the development of geophysical applications of fiber sensing within Ifremer. The supervising team of four researchers belonging to Geo-Ocean (Ifremer and CNRS) are involved in several ongoing projects that address the France 2030 initiative ‘Deep Ocean” such as Fiberscope and Tamtam. You will also have the opportunity to acquire more DAS data during the project, taking part in additional DAS acquisitions within the ALMA team. As part of the PhD program, you will have opportunities for new training and skills development, with potential participation in data acquisition to gain experience in marine geoscience.

Benefits from the host institution

• This PhD is an opportunity to work on Ifremer's scientific and technological priority themes. It entitles the holder to a gross monthly salary of 2300 euros gross for a period of 3 years, which cannot be combined with other scholarships.
• We have a teleworking agreement and our staff have 12 comp time days and supra statutory leave.
• We allocate a significant budget to developing skills, through individual or collective training actions.
• We have a CSR policy inspired by the purposes of the institute (sustainable mobility allowance, etc.)

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Title

PHD : Seismic Characterisation of Active tectonic Fault with Fiber Optic - Sensing: application to the North Alfeo strike-slip Fault (M/F)*

Published

2025-03-31

2025-05-19 23:59 (Europe/Paris)
2025-05-19 23:59 (CET)

Ifremer conceives and operates tools for observation, experimentation and monitoring, and manage the oceanographic databases.