Splay fault activity revealed by aftershocks of the 2010 Mw 8.8 Maule earthquake, central Chile

Splay faults, large thrust faults emerging from the plate boundary to the seafloor in subduction\nzones, are considered to enhance tsunami generation by transferring slip from the\nvery shallow dip of the megathrust onto steeper faults, thus increasing vertical displacement\nof the seafloor. These structures are predominantly found offshore, and are therefore difficult\nto detect in seismicity studies, as most seismometer stations are located onshore. The Mw\n(moment magnitude) 8.8 Maule earthquake on 27 February 2010 affected ~500 km of the central\nChilean margin. In response to this event, a network of 30 ocean-bottom seismometers was\ndeployed for a 3 month period north of the main shock where the highest coseismic slip rates\nwere detected, and combined with land station data providing onshore as well as offshore coverage\nof the northern part of the rupture area. The aftershock seismicity in the northern part\nof the survey area reveals, for the first time, a well-resolved seismically active splay fault in the\nsubmarine forearc. Application of critical taper theory analysis suggests that in the northernmost\npart of the rupture zone, coseismic slip likely propagated along the splay fault and not the\nsubduction thrust fault, while in the southern part it propagated along the subduction thrust\nfault and not the splay fault. The possibility of splay faults being activated in some segments of\nthe rupture zone but not others should be considered when modeling slip distributions.