The Mw 8.3 Illapel earthquake (Chile): Preseismic and postseismic activity associated with hydrated slab structures

The accumulated stress in subduction zones is discharged with earthquake and aseismic activity; the latter is hosted in rheological complex regions, characterized by high pore fluid pressure, and is often accompanied by repeated earthquakes and earthquake swarms. The spatiotemporal analysis of seismic activity can reveal the presence of aseismic transients associated with large earthquakes. Here we study 20 years of seismicity prior to and after the M-w 8.3 earthquake that occurred in A.D. 2015 in central Chile. We identified several earthquake swarms before the main shock and repeating aftershocks at the border of the main slip area. Spatial clustering of the seismic activity shares similar orientation with the main fracture zones observed on the outer rise of the subducting Nazca plate. Our findings suggest that the fracture zones enclosing the rupture are playing a major role in accommodating the pre and post-main shock stress evolution. We further recognize how fracture regions have acted as barriers to the propagation of large earthquakes in the region.