PhD student in seismology and luminescence dating (M/F)

Job Description

Thesis Subject

Keywords: Optically stimulated luminescence (OSL) dating of sediments and rocks, palaeoseismology, megaliths, Bayesian chronological modelling, archaeoseismicity, stable continental regions (SCR), Armorican Massif.
Context and description of the thesis topic
Stable continental regions (SCR) are characterised by low to moderate seismicity (Ml < 3) but punctuated by strong events (e.g. the Le Teil earthquake in 2019 or the La Laigne earthquake in 2023, Ml > 5). These events, often associated with the reactivation of inherited faults, leave traces in geological and archaeological structures that are sometimes difficult to identify and date accurately. The ANR FaSiRé project, led by C. Perrin (Laboratory of Planetology and Geosciences, CNAP/Univ. Nantes), aims to fill this gap by combining geomorphological, palaeoseismological and archaeological approaches focused on the Armorican massif in order to shed light on its Quaternary seismic history. To this end, several objects will be studied as part of the FaSiRé project: the deformation of sediments in the vicinity of known faults and earthquakes (e.g., Ritz et al., 2021), megaliths (menhirs, steles, tumuli) that may have collapsed due to ground movements following an earthquake (e.g., Boujot & Cassen 2000), and natural rocks in precarious equilibrium (or 'PBR') that did not fall during past seismic events (e.g. McPhilips & Pratt, 2024). Each analysis will provide important information for estimating the minimum and maximum magnitudes of past regional earthquakes. One of the key challenges of the FaSiRé project is to determine the age of regional deformations, taking into account the possible evolution of the landscape over time due to erosion processes. A robust characterisation relies in particular on the need to have a large number of measurements from several study sites. The objective of this thesis is therefore:
- To carry out a systematic inventory of PBRs based on existing databases, as well as on the analysis of HD LiDAR (IGN) and satellite topographic data. This first step will enable us to target study areas where the density of PBRs is particularly high.
- To carry out optically stimulated luminescence (OSL) dating of the surface of PBR rocks and their substrate in order to determine the maximum age of objects that have not undergone critical seismic shocks. These results will help to better constrain 1) regional seismic hazard, 2) the rates of alteration of PBRs and the evolution of their geometry, and 3) the evolution of the appearance of anthropogenic megaliths since the Neolithic period. The ages obtained will also be compared with existing regional erosion rate datings.
- Participate in archaeological and paleoseismological surveys to date sediments and/or rock surfaces by optically stimulated luminescence (OSL) affected by deformation (faults) or covered by collapsed megaliths. All of the data will be used to build chronological models in order to test, among other things, the hypothesis of contemporaneity between earthquakes and collapses. More generally, the objective will be to better understand the seismicity of the Brittany region over the last few millennia. The PhD student recruited will mainly develop skills in OSL dating, but also in topographic data processing (e.g., LiDAR), with applications at the interface between Earth sciences and archaeology.
The skills sought for this thesis include a master's degree in Earth Sciences, Physics or Archaeology, with an appetite for geochronology, laboratory work, GIS analysis and programming.
Work context
The proposed thesis is part of work package 2 of the ANR FaSiRé (Archeo-seismicity) project, led by C. Perrin. The work will involve:
- image analysis and mapping of the objects studied;
- field missions to carry out observations, in situ luminescence measurements and sampling;
- luminescence and natural radioactivity measurements in the laboratory at the Géosciences Rennes site (Rendal platform);
- chronological modelling using software developed in R language.
This work will be carried out in close collaboration with other PhD students in the FaSiRé project who will be working on geomorphological and seismotectonic analysis, as well as numerical modelling of the conditions of megalith and PBR falls. There will be numerous collaborations and discussions with the project's multidisciplinary team (physicists, seismologists and archaeologists).
Supervision and contact
Guillaume Guérin (Géosciences Rennes): guillaume.guerin@univ-rennes.fr
Philippe Steer (Géosciences Rennes): philippe.steer@univ-rennes.fr
Clément Perrin (Laboratoire de Planétologie et Géosciences, Nantes): clement.perrin@univ-nantes.fr
References
Boujot, C., & Cassen, S. (2000). Tertres et pierres dressées. Eléments d'architecture, Association des Publications Chauvinoises, Chauvigny, 181-206. McPhillips, D., & Pratt, T. L. (2024). Precariously balanced rocks in northern New York and Vermont, USA: ground‐motion constraints and implications for fault sources. Bulletin of the Seismological Society of America, 114(6), 3171-3182. doi.org/10.1785/0120240069 Ritz, J. F., Baize, S., Audin, L., Authemayou, C., Graveleau, F., Kaub, C., ... & Van der Woerd, J. (2021). New perspectives in studying active faults in metropolitan France : the “Active faults France”(FACT/ATS) research axis from the Resif-Epos consortium. Comptes Rendus. Géoscience, 353(S1), 381-412. doi: 10.5802/crgeos.98

Your Work Environment

Géosciences Rennes is a joint research unit (University of Rennes and CNRS) with 150 staff, including 60 researchers and lecturers, specialising in the study of geological and environmental processes.

Compensation and benefits

Compensation

2300 € gross monthly

Annual leave and RTT

44 jours

Remote Working practice and compensation

Pratique et indemnisation du TT

Transport

Prise en charge à 75% du coût et forfait mobilité durable jusqu’à 300€

About the offer

About the CNRS

The CNRS is a major player in fundamental research on a global scale. The CNRS is the only French organization active in all scientific fields. Its unique position as a multi-specialist allows it to bring together different disciplines to address the most important challenges of the contemporary world, in connection with the actors of change.

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