Short term interseismic coupling and lateral variation along the Mexican subduction from remote sensing

Abstract:

The Mexican subduction is a complex region where different deformations behaviors are can be observed. In this region, numerous earthquakes occur with a recurrence time between 30 and 70 years with magnitudes up to Mw 8 (e.g., Michoacán 1985; Jalisco 1995), associated with post-seismic displacements. This region is also affected by large slow slip events documented in the Guerrero and Oaxaca areas. These various observations highlight the complexity of this subduction and the importance to study the interseismic coupling in relation to these different slip behaviors. One of the major challenges of this study is to image the Mexican subduction surface deformation at large scale over a 1,000 km long zone, and evaluate its coupling variability.

In this region, the GNSS network's spatial density does not have sufficient resolution to study and measure the variability of the surface deformation all along the subduction. To improve the spatial coverage of interseismic deformation estimates, we propose to combine InSAR and GNSS data. We use four Sentinel-1 descending tracks covering an important part of the Mexican subduction from Jalisco to Oaxaca, over a period from 2016 to 2019. The InSAR and GNSS time series, over the same 3-year period, are corrected from co-seismic deformations but not from aseismic slip (slow slip event and post-seismic). We present estimates of mean velocities over the study period, representing interseismic and non-interseismic slow slip events velocities. By inverting these velocities, we estimate the instantaneous coupling at the interface, which show large lateral variations along the subduction. InSAR data significantly improves the resolution of the inversion, as we show by comparing it to a model based only on GNSS data. Although not representative of long-term coupling in areas of transient events, the instantaneous coupling estimates highlights the role of transient signals, such as slow slip events, on the coupling variability measured by spatial geodesy. In agreement with GPS times series over longer time period, it also suggest that the Jalisco area (-106° and -104°) is highly coupled with a coupling value higher than 0.8.