The super-interseismic phase of the megathrust earthquake cycle in Chile

Abstract

Along a subduction zone, great megathrust earthquakes recur either after long seismic gaps lastingseveral decades to centuries or over much shorter periods lasting hours to a few years when cascadingsuccessions of earthquakes rupture nearby segments of the fault. We analyze a decade of continuous GlobalPositioning System observations along the South American continent to estimate changes in deformation ratesbetween the 2010 Maule (M8.8) and 2015 Illapel (M8.3) Chilean earthquakes. Wefind that surface velocitiesincreased after the 2010 earthquake, in response to continental-scale viscoelastic mantle relaxation and toregional-scale increased degree of interplate locking. We propose that increased locking occurs transientlyduring a super-interseismic phase in segments adjacent to a megathrust rupture, responding to bending of bothplates caused by coseismic slip and subsequent afterslip. Enhanced strain rates during a super-interseismicphase may therefore bring a megathrust segment closer to failure and possibly triggered the 2015 event.