Geodetic slip inversion for the 2017/18 SSE and associated earthquakes near Guerrero, Mexico

In Guerrero, Mexico, slow slip events (SSEs) occur every 3-4 years in a region without M W >8 megathrust earthquakes since 1911. Previous work measuring slip in the SSEs relied primarily on a sparse network of Global Navigation Satellite Systems (GNSS) measurements, which limited ability to fully constrain the spatial extent of slip. We use L-band ALOS-2 InSAR observations to supplement the GNSS network and estimate slip and moment for the most recent (2017/18) event. InSAR provides spatially dense measurements but is challenged by decorrelation and atmospheric noise. The most recent Guerrero SSE began in July 2017 and ended in 2018, with several earthquakes occurring during the time period (the September 2017 Mw 8.1 Chiapas and Mw 7.0 Puebla earthquakes and the February 2018 Mw 7.1 Oaxaca earthquake). The combined SSE and postseismic deformation from these earthquakes lasted until at least June 2018. We generate time-series for three ALOS-2 tracks (152, 153, and 155) covering the period between March 2015 and January 2019. We correct for ionospheric and tropospheric noise and estimate cumulative offsets due to the slow slip event and the 2018 Oaxaca and 2017 Puebla earthquakes. We jointly invert the InSAR offsets with GNSS offsets to solve for slip on the subduction zone in southern Mexico, accounting for the full error covariance of the InSAR observations. The combined dataset resolves additional details of the slip distribution compared to GNSS alone. Aseismic slip occurs outside seismogenic regions of the fault interface, and the SSE was accompanied by extensive afterslip following regional earthquakes. The combined (aseismic) moment release from the SSE + afterslip following the Oaxaca earthquake was equivalent to M W 7.4-7.6.