Size and timing of giant Chilean earthquake controlled by rock composition and forearc structure

Abstract

Abstract In 1960, the Southern Chile subduction zone produced the Mw9.5 Valdivia mega-quake, the largest earthquake on record, breaking up the entire seismogenic zone for 1,000 km along the Chile Trench. Crustal deformation in the aftermath involved a combination of fault motion and viscoelastic flow. The region has recovered its seismic potential, as evidenced by the 2016 Mw7.6 Melinka earthquake that only partially affected the 1960 rupture zone below the continental shelf. The succession of such partial and full ruptures at subduction megathrusts controls seismic hazards but remains poorly understood. Here we show how the distribution of frictional and rheological properties within the forearc and the surrounding lithosphere, controls the size and timing of great and giant earthquakes at the Chile Trench. We build numerical simulations of the seismic cycle in Southern Chile using frictional and viscoelastic properties calibrated to geologic, geodetic, and geophysical information. The model explains the recurrence times of great and giant earthquakes from paleoseismic data, but also the fault slip distribution and crustal deformation associated with the Melinka and Valdivia earthquakes. Our synoptic model illuminates the structural and geological controls on seismicity, explaining the typical sequence of blind and trench-breaking ruptures at subduction zones.