New 2010 Maule aftershock catalog reveals structure of the deep subduction interface

On February 27th 2010, a Mw 8.8 earthquake occurred near Maule in south-central Chile. The subsequent rapid deployment of a dense network of seismic stations on land was able to capture the first year of its aftershock sequence. Here, we revisit this dataset using picking Artificial Intelligence tools, a 3D velocity model of the region and double-difference techniques, to obtain a catalog of 215582 aftershocks, including 146950 well-constrained events. We observe many features first documented by studies using less dense aftershock catalogs, including the presence of important outer rise seismicity in the north, the occurrence of small earthquake sequences in the volcanic arc, the pervasive faulting associated with the Mw 6.9 March 11th 2010 Pichilemu, and the separation of plate interface seismicity into two groups located at 15-40 km depth and 40-55 km depth. We focus on the deeper part of the plate interface seismicity (40-55km depth), located in the transition zone at the bottom of the seismogenic zone, to investigate its structure. In this region, earthquakes tend to occur on juxtaposed planes within a ~1.6 km thick zone. Many of these events form 100m to km scale long streaks aligned along dip, which might be linked to the presence of afterslip in the region. Knowing that the subduction interface at this depth likely has a block-in-matrix structure, we speculate that these small lineations may occur within individual blocks smeared along the subduction, or alternatively that they may occur within aligned chains of blocks jamming the subduction.