Quantifying interseismic deformation along the Mexican subduction zone from Sentinel-1 InSAR time series

Understanding how stresses accumulate and release along subduction zones, the regions hosting the world largest earthquakes, is essential for a better assessment of seismic hazard. Monitoring the surface deformation of the upper plate allows to infer processes taking place along the subduction interface during the different phases of the seismic cycle. Here we focus on the Mexican subduction zone, where large damaging earthquakes frequently occur. This subduction zone also hosts large and frequent slow slip events (SSEs) that are predominantly aseismic. Using geodetic techniques (InSAR and GNSS) along the 1000 km of the Mexican subduction zone allows different modes of slip mode to be investigated (interseismic, post-seismic, slow slip), but is challenging. Previous studies have shown the slow slip event and interseismic signal can be extracted from InSAR observation 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 analyze the extended Sentinel-1 InSAR dataset, processed through the French national FLATSIM facilities (The ForM@Ter LArge-Scale Multi-Temporal Sentinel-1 InterferoMetry Service) covering the 2016-2022 period. The post-processing of the FLATSIM data includes several steps. First, the noisy pixels (i.e., affected by low-coherence, unwrapping errors) or non-tectonic signals (strong subsidence) are masked using the quality indicators of the FLATSIM products. Then, we correct the InSAR time from co-seismic offsets using a parametric model, since several earthquakes occurred during the study period, and estimate for each pixel a linear trend corresponding to the interseismic deformation. We finally adjust the different tracks in a common reference frame, by correcting, for all the tracks, from ramp to adjust (1) the InSAR signal to the GNSS estimate for the same time period and (2) the coherency between the overlap zones of adjacent tracks. The result is a homogeneous map of interseismic deformation over the whole Mexican subduction zone for the period 2016-2022. Some areas are affected by post-seismic deformation and large slow slip events (in Guerrero and Oaxaca region), that should be taken into account when analysing coupling map of the subduction.