Slow slip events in Mexico revised from the processing of 11 year GPS observations

The world's largest observed Slow Slip Events (SSE) occurred in 2001-2002 and 2006 in the Guerrero subduction zone, Mexico. Using an improved GPS processing that accounts for time-varying atmospheric phenomena as well as oceanic, atmospheric and hydrologic loading corrections, the 11 year GPS position time series in Guerrero show a noise reduction of ∼50% with respect to previous studies. Thanks to the improved position time series and, in particular, the simultaneous analysis of the three-dimensional GPS observations, we can provide new information about SSEs in the studied area. First, we detect seven nonperiodic anomalous displacements with subcentimeter amplitude, but no quasi-annual anomalies as proposed previously. The displacements seem to occur simultaneously with the observed peaks of non-volcanic tremor activity in the area. Second, we refine the characteristics of the two major SSEs in terms of timing, duration, and cumulative displacements, and highlight the complex surface spatiotemporal evolution of the displacements during these SSEs. In particular, we observe a clear initiation phase for the 2006 SSE as well as ending phases for both large SSEs. The ending phase shows a strong deceleration of the anomalous displacements with respect to the main displacement phase already observed, for the 2001-2002 and 2006 SSEs. The duration of the SSEs increases by 30-40% including the initiation and ending phases. For the 2006 SSE, the main displacement phase also shows spatiotemporal complexity. Our results demonstrate the need for improved three-dimensional GPS processing technique in order to undertake detailed studies of SSEs.