Recurrence Time and Down-Dip Size of Chilean Earthquakes Influenced by Geological Structure

Abstract

Abstract In 1960, the giant Valdivia earthquake (Mw 9.5), the largest earthquake ever recorded, struck the Chilean subduction zone, rupturing the entire depth of the seismogenic zone and extending for 1,000 km along strike. The first sign of new seismic energy release since 1960 occurred in 2017 with the Melinka earthquake (Mw 7.6), which affected only a portion of the deepest part of the seismogenic zone. Despite the recognition that rupture characteristics and rheology vary with depth, the mechanical controls behind such variations of earthquake size remain elusive. Here, we build quasi-dynamic simulations of the seismic cycle in Southern Chile including frictional and viscoelastic properties, drawing upon a compilation of geological and geophysical insights, to explain the recurrence times of recent, historic, and paleoseismic earthquakes and the distribution of fault slip and crustal deformation associated with the Melinka and Valdivia earthquakes. The frictional and rheological properties of the forearc, primarily controlled by the geological structure and distribution of fluids at the megathrust, govern earthquake size and recurrence patterns in Chile.