The deep subduction earthquake machine: A synoptic view of the Chile Subduction Zone.

In the last 20 years, the Chile Subduction Zone (CSZ) has hosted two deep-located subduction events, the 2007 Mw 7.7 Tocopilla earthquake at the Mejillones Peninsula, and the 2016 Mw 7.6 Melinka earthquake at the south of the Chiloé Island. Interseismic seismicity at the Northern and Southern segments of the CSZ, show that in both cases, the ruptures initiated at the down-dip limit of the seismogenic zone. Locking degree models suggest that hypocenter location of this kind of megathrust earthquakes is spatially related with the transition from strongly to weakly locked areas. There are major differences in fault geometry, temperature-pressure regime, petrology at the plate interface and forearc structure between the North and South of the CSZ, raising the question about how such different tectonic settings allow a similar style of rupture. By constructing geologically and geophysically constrained dynamic numerical simulations, here we show that moderate-to-large deep nucleated earthquakes are controlled by petrology and pressure-temperature conditions at the plate interface, along with the structure of the forearc wedge. Our results explain the occurrence, recurrence times and coseismic upper crust deformation of both earthquakes, suggesting that blind ruptures are not only generated at specific conditions, but a suitable combination of the aforementioned parameters is needed. Since the Northern Chile subduction zone has no sediments at the megathrust, the frictional behavior is controlled by altered basalt at the seismogenic depth, and seismicity shows a strong temperature-dependence. Once altered basalt no longer behaves as a velocity weakening material, blueschist rocks allow slow-slip events to develop. The Southern Chile subduction zone is filled with Pliocene-to-present sediments feeding a quartz-dominated subduction channel that defines the seismogenic limit. Within this framework, basal accretion structures are overlapped with a fluid concentration zone at the Moho depth, where the Melinka earthquake initiated. These synoptic views of the CSZ manifest a strong interaction between fluid-rock and forearc structures, which explains the occurrence of blind ruptures at the subduction seismic cycle.