Slow Slip Events and degree of coupling along the Mexican subduction zone in Guerrero and Oaxaca areas: role of the slab geometry and its lateral variations, spatio-temporal evolution, slip budget, determined from cGPS time series inversion using PCAIM code

Abstract:

Since the first cGPS have been installed in 1997 in the Guerrero-Oaxaca region of the Central American subduction zone in Mexico, several slow slip events (SSE) have been observed there. Further studies showed that the SSE characteristics are disparate in Guerrero and Oaxaca in terms of duration, amplitude and depth. In particular, recent investigations show that the slip during SSE intrudes the seismogenic zone in Guerrero, but barely in Oaxaca. The SSE lateral and depth extent has important implications on the seismic cycle. It affects the redistribution of stress (increasing or decreasing it) within the seismogenic zone, thus the timing and magnitude of future earthquakes.  It is thus important to constrain a degree of coupling on the subduction interface and how the coupling evolves in space and time. This can be achieved by refining coupling models based on the observations and exploring a sensitivity of the models to variations of their main parameters.

To better understand the effect of the SSE on the seismic cycle along the Mexican subduction zone, we analyze cGPS data and invert the time series, using a method based on a principal component analysis: PCAIM (Principal Component Analysis-based Inversion Method). For both Guerrero and Oaxaca areas, we first discuss the geometry of the plates’ interface. Then we investigate in particular the effect of possible lateral and down-dip variations of the subduction interface on coupling models. Subsequent modeling using the PCAIM of the sequential SSEs that occurred in the past decade permitted to compare our results with the inferences of previously published works. We present the first analysis of the latest large SSE that started in January 2014 in Guerrero. We show that the PCAIM allows to describe a complex slip history in space and time of different SSEs and to provide a comparative analysis of behavior of the individual SSEs. We then discuss the potential interplay between SSE in Guerrero and Oaxaca, and the link between them and seismicity. Finally, we interpret our coupling map in terms of slip budget and seismic hazard in Guerrero and Oaxaca areas.