Quantifying interseismic loading and slow slip events in the Mexican subduction zone at large scale using satellite SAR interferometry time-series analysis

6 months, starting January or February 2024

Subduction zones host the world largest earthquakes, and understanding how stresses accumulate and release along these plate boundaries is essential for a better assessment of the seismic hazard.
In subduction zones, thanks to the monitoring the surface deformation of the upper plate, we can infer the processes taking plate along the subduction interface, during the different phases of the seismic cycle. In particular, during the loading periods (i.e. interseismic), it is possible to characterize the interseismic coupling along the plate interface. Coupling equals 1 when the plate interface is locked, i.e. strain and stress are accumulating, and coupling equals 0 when the interface is slipping freely.
Surface deformation also allows us to characterize the various slip modes that participate to the release of stresses. The slip between tectonic plates along the subduction interface is a combination of seismic (i.e. earthquakes) and aseismic slip (i.e. slow slip events, post-seismic), and understanding the partitioning between these modes of slip is important to understand the seismic potential of faults.
In this project, we propose to focus on the Mexican subduction zone, where large damaging earthquakes frequently occur, as illustrated by the recent 19 September 2022 Mw=7.6 earthquake in the Michoacan region. This subduction zone hosts large and frequent slow slip events (SSEs) that are mostly aseismic (Radiguet et al 2012). We propose to exploit two surface geodetic techniques to monitor the surface deformation : InSAR observation from the Sentinel-1 satellites and GPS. Previous studies done by our team have shown that both slow slip and interseismic signal can be extracted from this dataset (Maubant et al 2020, Maubant et al 2022), but have been limited to the 2016-2019 period, and were not completely homogeneous in term of processing. The large amount of data needed to cover the whole Mexican Subduction zone was one challenging issue.
Here, we would like to extend our analysis to the 2016-2022 period by taking advantage of our previous experience but also of the availability of the national FLATSIM facilities (The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service, https://www.poleterresolide.fr/projets/en-cours/flatsim/). This service massively generated thousands of interferograms and associated products, such as the time-series of surface displacement using the NSBAS methods (Ho Tong Minh et al. 2022). 11 InSAR tracks have been processed and cover the whole Mexican subduction (1000 km x 500km area), which provides an homogeneous set of data.
A first part of the work will consist in post-processing the FLATSIM InSAR data, following the methodology developed during a previous Master project (Meridi, 2023) to mask the regions with processing errors and/or non tectonic signals. Then, the different sources of tectonic deformations present in the deformation time series will be separated. In particular (1) the surface displacement associated with each recent earthquakes in the time series will be estimated and corrected, (2) the interseismic loading velocities will be estimated and (3) when possible, the deformation associated with slow slip events will be extracted. Finally, the extracted surface deformation fields (both InSAR and GPS) will be inverted to infer the interface coupling as well as the slip associated with the SSEs. This work will allow to better quantify the interseismic loading and slow slip events contributions to the seismic cycle in the Mexican subduction zone, over a large spatial scale.
This internship will be part of the ANR project SSDYN “Identifying slow slip dynamics combining seismic and geodetic data”. This project funded by the French Research Agency (ANR) is lead by Mathilde Radiguet. It involves Mexican and French scientists from 5 different research institutions. The student will be hosted at ISTerre a multidisciplinary laboratory, whose research focuses primarily on the physical and chemical study of the planet Earth. This context provides an ideal setting for the students to engage in scientific discussions and to develop skills in various domains.

What can you gain from this internship ?
• Get into exciting scientific questions related to the earthquake cycle working on one of the best-documented subduction zone showing large slow slip events.
• Learning advanced technique in InSAR processing
• Learning tools to separate different source of deformation mixed in time-series of surface displacement signal
• Learning to process large datasets on the intensive computing infrastructure provided by University (GRICAD)
Required Skills :
Curiosity and interest for the earthquake cycle.
Interest for programming and for working on large data sets using computing center.

Bibliography :
Ho Tong Minh, D., Hanssen, R., Doin, M.-P., & Pathier, E. (2022). Advanced Methods for Time-series InSAR. In Surface Displacement Measurement from Remote Sensing Images (pp. 125–153). John Wiley & Sons, Ltd. https://doi.org/10.1002/9781119986843.ch5
Maubant, L., Pathier, E., Daout, S., Radiguet, M., Doin, M.-P., Kazachkina, E., Kostoglodov, V., Cotte, N., & Walpersdorf, A. (2020). Independent Component Analysis and Parametric Approach for Source Separation in InSAR Time Series at Regional Scale : Application to the 2017–2018 Slow Slip Event in Guerrero (Mexico). Journal of Geophysical Research : Solid Earth, 125(3). https://doi.org/10.1029/2019JB018187
Maubant, L., Radiguet, M., Pathier, E., Doin, M.-P., Cotte, N., Kazachkina, E., & Kostoglodov, V. (2022). Interseismic coupling along the Mexican subduction zone seen by InSAR and GNSS. Earth and Planetary Science Letters, 586, 117534. https://doi.org/10.1016/j.epsl.2022.117534
Radiguet, M., Cotton, F., Vergnolle, M., Campillo, M., Walpersdorf, A., Cotte, N., & Kostoglodov, V. (2012). Slow slip events and strain accumulation in the Guerrero gap, Mexico. Journal of Geophysical Research : Solid Earth, 117(B4), n/a-n/a. https://doi.org/10.1029/2011JB008801
Radiguet et al 2022, ANR project proposal SSDYN, “Identifying slow slip dynamics combining seismic and geodetic data
Thollard, F., Clesse, D., Doin, M.-P., Donadieu, J., Durand, P., Grandin, R., Lasserre, C., Laurent, C., Deschamps-Ostanciaux, E, Pathier, E., Pointal, E, Proy, C., Specht, B. (2021). FLATSIM : The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service, Remote Sens. 13 (18), 3734. doi:10.3390/rs13183734, HTML
Meridi A. (2023) Interseismic loading and slow slip events in the Mexican subduction zone : quantification using satellite SAR interferometry time-series analysis ; Master2 internship Fev. Jul. 2023 ISTerre, Phitem UGA