Splay fault slip during the Mw 8.8 2010 Maule Chile earthquake: COMMENT

Over the past decade, the Isla Santa María (south-central Chile) has provided one of the most exquisitely detailed records of deformation and tectonically controlled sea-level change anywhere along the Andean margin (Bookhagen et al., 2006; Melnick et al., 2006, 2009, 2012). This work has been combined with extensive offshore suites of data, especially seismic reflection profiles and local and regional geophysical studies, to provide an unparalleled view of the offshore portion of the southern Chilean forearc. Melnick et al. (2012) recently postulated the activity of a splay thrust fault, the Santa María Fault System (SMFS), during the 2010 Maule earthquake. This work is timely given current interest in the role of splay faults in contributing to total moment release during great subduction zone earthquakes, local tsunami hazard, and rupture segmentation. Given the importance, one must ask whether their evidence is so compelling as to require the activity of a splay thrust, especially considering that their field observations show only normal fault activity.