Using Global Positioning System (GPS) receivers and acoustic transponders, Gagnon et al. (2005) estimate that the measured horizontal surface motion perpendicular to the trench (in western border of the Lima peruvian coastal region) is consistent with a model having no slip along the thrust fault between 2 and 40 km depth. These results suggest that the updip limit of the seismogenic zone is relatively shallow giving rise to potentially larger tsunamis.
A tsunami in 1996, 200 km north of the locked zone, was interpreted as being the result of an anomalously shallow interplate earthquake (now called Tsunami-Earthquakes). Seismic coupling at shallow depths, such as is observed, may explain why co-seismic events in the Peruvian subduction zone create large tsunamis.