The Constituciَn earthquake of 25 March 2012: A large aftershock of the Maule earthquake near the bottom of the seismogenic zone

The Mw 7.0 Constituciَn earthquake of March 2012 is one of the largest interplate aftershocks of the Maule 2010 Mw 8.8 mega-thrust earthquake. This event was recorded by high-rate GPS stations, local seismometers and accelerometers, the Global Seismographic Network and SAR acquisitions by the ENVISAT satellite. We have used these data to perform a kinematic inversion and back projection to identify the principal characteristics of this event. The Constituciَn earthquake nucleated at 39 km depth and then propagated up-dip at subshear speed towards its centroid, with an unusually long initiation phase that lasted almost 6 s. The largest slip of this event was located in the deeper part of the subduction interface, between the region of maximum co-seismic slip of the 2010 Maule earthquake, and the area where rapid afterslip occurred following that event. Features of the Constituciَn earthquake may suggest that larger interplate aftershocks of the Maule event preferentially occur in the deeper part of the plate interface where ruptures are complex, produce high frequencies and involve numerous asperities.