Interseismic loading and slow slip events in the Mexican subduction zone : quantification using satellite SAR interferometry time-series analysis

6 months, Starting January or February 2023

Subduction zones host the world largest earthquakes, and understanding how stresses accumulate and release along these plate boundaries is thus essential for a better assessment of the seismic hazard. 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 two modes of slip is important to understand the seismic potential of faults.

In this project, we propose to focus on the Mexican subduction zone, which frequently hosts large damaging earthquakes, as illustrated by the recent 19 September 2022 Mw=7.6 earthquake in the Michoacan region, but it is also the place of large and frequent slow slip events (SSEs) that are mostly aseismic (Radiguet et al 2012).

One way to study aseismic slip is to measure the surface deformation using geodetic techniques like GPS or InSAR (satellite SAR interferometry). Here, in complement to work being done on GPS data in our team, we propose to exploit InSAR observation from the Sentinel-1 satellites. Previous studies done by our team have shown the feasibility of the approach (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 will start at the autumn 2022 to massively generate thousands of interferograms and associated products over the whole Mexican subduction (1000 km x 500km area), which will provide an homogeneous set of the data needed to generate the time-series of surface displacement.

In this project, the student will focus on a limited 250 km x 500 km area, covering the Guerrero region where several SSEs occurs during the 2016-2022 period. A first part of the work will be to establish a methodology to perform the post-processing of the FLATSIM InSAR data, that is to create corrected InSAR time-serie from the interferogram using the NSBAS methods (Ho Tong Minh et al. 2022). The second part will consist in the time-series analysis to separate the different sources of signal that are mixed in the InSAR time-series (deformation signals related to the seismic cycle, hydrological signal or residual atmospheric effect) in order to better quantify the interseismic loading and slow slip events contributions to the seismic cycle in the Mexican subduction zone.

This internship will be part of an exciting starting project called 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