Geodetic Measurements of the Guerrero Slow Slip Events: Implications for Large Earthquakes in the Guerrero Gap

Abstract:

Estimates of elastic strain accumulated in the Guerrero seismic gap, Mexico, have conceived a potential for Mw 8.0-8.4 subduction thrust earthquake. While several large slow slip events (SSEs) have occurred in the area it remains unclear how the SSEs change the stress field in the Guerrero seismic region, and what their implications are for future devastating earthquakes. On 18 April 2014, the Mw 7.2 Petatlan earthquake, followed by two Mw 6.4 and 6.1 events on 8 and 10 May 2014, occurred on the western edge of the Gap, while a new large slow slip event was ongoing, suggesting that it may have triggered the earthquakes.

Slow slip studies have mainly relied on GNSS. In Guerrero the low station distribution restricts their ability to resolve the spatial extent of the SSE. We apply a time-series Interferometric Synthetic Aperture Radar (InSAR) analysis to estimate the spatial extent and magnitude of deformation caused by a slow slip event in 2006, and jointly invert GNSS and InSAR for slow slip on the subduction interface. We assume rectangular dislocation patches, and use Markov chain Monte Carlo sampling to obtain a full error distribution of the model unknowns. Correlation between our estimated slow slip region and the location of non-volcanic tremor, as well as an ultra-slow velocity layer, supports the hypothesis of a common source potentially related to high pore pressures. We find slow slip extends up to 7 km depth, well within the Guerrero Gap. We observe a spatial correlation between slow slip and a high slip deficit region. Even accounting for the stress released by SSEs, we find the Guerrero Gap still has a potential for Mw ~7.8-8 earthquake.

We also present results for the 2014 SSE, using RADARSAT-2 data. We analyse whether slow slip could triggered the recent earthquakes, by investigating the spatial extent of the SSE and its relationship to the coseismic slip. Our results have implications for the timings of megathrust earthquakes in other subduction zones.