Institut de physique du globe de Paris - CNRS

The work will be carried out between IPGP and the GIEC experiemental lab., which is located about 1h from IPGP.
IPGP has been a leading research institution in earth sciences for more than 100 years. Most of the field of earth sciences are covered at IPGP.
The tectonic lab. of IPGP is very experienced in studying active faults and earthquakes in continental setting.
IPGP includes about 150 faculties including 10 faculties in tectonics.
The GIEC has an unique expertise in analogue modeling. It has been conducting collaborative work with IPGP for several years now.
This project is part of the ERC BE_FACT project led by Y. Klinger that is focussed on the earthquake cycle and the mutual interaction between earthquake rupture dynamics and fault geometry evolution.

Homepage: https://www.ipgp.fr

Strike-slip fault system and earthquakes in 4D, an analogue approach

Keywords: active strike-slip faults, 3D deformation distribution, analogue modelling.

Context and Objectives
Large-magnitude earthquakes (e.g. the 2023 Mw 7.8 Turkey earthquake doublet) produce spectacular sur-face deformations along active fault systems. In order to improve the assessment of seismic hazard and reduce the impact of such events, it is necessary to develop a finer understanding of the dynamics of earthquakes. However, the current state of knowledge regarding the physical processes governing earth-quake ruptures, the relation between rupture propagation, slip distribution and fault geometry, and the evolution of the fault geometry through successive earthquake cycles remains limited.
The project “BE_FACT”, funded by the European Research Council (ERC), aims to address this knowledge gap by leveraging machine learning (ML) and computer vision methodologies to derive earthquake source models and, thus, to provide new insights into the physics of earthquake rupture processes and the evolu-tion of the fault geometry trough earthquake cycles. To apply these new innovative strategies, the key is to produce a complete dataset to be used as learning dataset for the ML.
Hence, in the framework of BE_FACT we propose to conduct experimental analogue modelling of strike-slip faults, including earthquake cycles, to improve our understand of fault evolution and earthquake phys-ics and, at the same time, to populate the learning dataset.
The proposed approach combines X-ray scanning techniques (CT scan) with image-processing tools used for petroleum data analysis (Schreurs et al., 2003; Zwaan et al., 2021) to image the evolution of the fault system geometry through time. This approach will enable the imaging of structural growth and the quan-tification of 3D deformation during the temporal evolution of the strike-slip fault system.
This experimental approach will be first applied to conventional sandboxes, providing an accurate infor-mation on the temporal evolution of the fault geometry in 3D. Then, thanks to the development of innova-tive earthquake laboratory-scaled physical model for strike-slip faults, the same experimental approach will be used to study the evolution of the 3D geometry of the fault system subjected to series of earth-quakes. This new experimental approach will enable to address fundamental questions, such as: How does the geometry of the fault evolves during successive seismic cycles? What is this geometry at depth? How the geometry of complex fault systems impacts the earthquake rupture processes (location of earth-quake initiation and end for example)?
Eventually, all these experimental simulations will be combined with numerical simulations (another work package of the BE_FACT project) to constitute a large learning database to train the ML and enhance its efficiency for subsequent applications to real data.
This postdoctoral project will allow us to fully exploit the potential of these models by producing high resolution observations of surface deformation and 3D fault geometry through time, a key ingredient to better understand earthquake mechanics and rupture evolution in a continental faulting context.

Methods and work program
The present study in earthquake ruptures and fault deformations is to be conducted within the following three work packages.
(i) To obtain high-resolution data in both time and space of the surface displacements during seismic events.
In order to enhance the data base on surface displacement, a series of experiments must be conducted by varying boundary conditions both in terms of geometry and stress. This series of experiments can be carried out with conventional sandboxes (long-term deformation). It can be supplemented by recent seismogenic sandbox developed at the ISTeP lab. By employing optical image correlation and stereo-photogrammetry, the horizontal and vertical surface displacement field of various strike-slip fault systems will be measured.
(ii) To measure 3D fault geometry.
The objective is to model the evolution of an analogue strike-slip fault system within a non-destructive X-ray Computed Tomography (XRCT) system. Applying Digital Volumetric Correlation (DVC) technique, we will obtain the 3D strain evolution through time (Adams et al, 2013). In parallel, we will measure the dis-tribution of the surface deformation of models in high resolution, using PIV techniques on surface models in the XRCT system (Zwaan et al, 2021). Thus, for each experience we will be able to characterize the full 4D evolution of the fault system (space and time). Repetition of experiments with different boundary con-ditions will provide us with a large experimental dataset about 3D fault-geometry time evolution and its relation with surface deformation. We plan to carry out this series of experiments in an institute equipped with a medical scanner (Institute of Geological Sciences of Bern University (Switzerland), IFPen, …).
(iii) 3D geometry of faults through seismic cycles.
Once the previous experimental protocol will be validated for conventional sandbox experiments, a similar setup will be used to image our experimental earthquake model. Those new experiments should give us a unique insight to determine how earthquake-rupture propagation and fault geometry are related in 4D to better understand the geometrical complexity of real earthquake ruptures.

Yann Klinger (klinger@ipgp.fr) and Pauline Souloumiac (pauline.souloumiac@cyu.fr). The candidate will be based in IPGP and will conduct the experiments at CY Cergy Paris University. The applicants are expected to send their curriculum and a brief summary of their past research experience and scientific results The names and contact information of two referees will also be provided.