Spatial and temporal evolution of a long term slow slip event : the 2006 Guerrero Slow Slip Event

P>The Guerrero 2006 Slow Slip Event (SSE), Mexico, one of the world's largest observed SSEs, was recorded at 15 continuous GPS stations. This event provides the opportunity to analyse in detail the spatial and temporal evolution of slip at depth, and to constrain the characteristics of a large SSE. We perform an inversion in two steps. First, we invert the cumulative GPS displacements to retrieve the total slip amplitude. Second, we invert for the initiation time and duration of the slip, using a linearized least-squares inversion procedure and assuming a functional form for the slip function. Our results show that the slip is located on a patch of 300 km x 150 km (parallel and perpendicular to the coast, respectively), and extends from the bottom of the seismogenic zone to the transition zone. This slow slip event has an equivalent moment magnitude of 7.5. The maximum slip over a length scale of 25 km is 15 cm and the mean slip is 5.5 cm. Its lateral extension coincides with the segmentation of the subduction. Our inversion scheme allows us to analyse the spatial variability of the rise time, rupture velocity and slip function. We obtain a continuous image of the spatial and temporal variations of slip on the fault plane. The rupture initiated at a depth of 40 km (transition zone), in the western part of the Guerrero gap. The rupture then propagated from the western to the eastern part of the Guerrero segment with an average velocity of 0.8 km d-1. Our results show that a slip dislocation pulse, characterized by a symmetric ramp function, can model the 2006 SSE. The rise time (local duration of slip) does not show large spatial variations and is equal to about 185 d. The local slip duration is compared to the total duration (11-12 months) of the event, suggesting a large interaction of a large part of the fault during the dynamic process. We find that our inverted slip model is well resolved on the shallow part of the fault and in the central section of the fault