Geodetic remote sensing constrains moment release from 2017/18 combined SSE and earthquakes near Guerrero, Mexico

The Guerrero seismic gap in Mexico has hosted several geodetically-observed slow slip events (SSEs), with the most recent event beginning in July 2017 and ending in 2018. Several earthquakes occurred during the same time and in the general region as the SSE: the Mw 8.1 Chiapas and Mw 7.0 Puebla earthquakes in September 2017, and the Mw 7.1 Oaxaca earthquake in February 2018. The combined SSE and postseismic deformation from these earthquakes lasted until approximately June 2018. We use observations from the ALOS-2 and Sentinel-1 SAR satellites and regional Global Navigation Satellite System (GNSS) stations in combination with time-series analysis to separate the interseismic from the coseismic and slow slip processes, and assess the associated stress changes to investigate potential triggering relationships between the SSE and the earthquakes. We generated InSAR time-series for three ALOS-2 tracks (152, 153, and 155) and two Sentinel-1 tracks (78 and 41) covering the complete Mexican subduction zone between March 2015 and January 2019 and correct these for both ionospheric and tropospheric noise. From the InSAR and GNSS time-series we estimate cumulative offsets for the slow slip event and the 2018 Oaxaca and 2017 Puebla earthquakes. We jointly invert InSAR and GNSS cumulative offsets to solve for slip on the subduction zone in southern Mexico, accounting for the full covariance of the InSAR observations. We apply a Bayesian analysis with MCMC sampling to obtain full posterior distributions for slip, rake, and a smoothness hyperparameter. We find a total moment release from the SSE equivalent to M W 7.3, a total co-/post-seismic moment release of M W 7.3 during the 2018 Oaxaca earthquake , and a total co-/post-seismic deformation during the 2017 Puebla earthquake of Mw 6.9. We find peak cumulative slip of 24 cm associated with the SSE, with the general extent similar to past events. Finally, we show the impact of the SSE on the local stress field through coulomb stress change analysis and discuss possible triggering relationships between SSEs and earthquakes on this part of the Mexico subduction zone.