Automated Earthquake Detection and Local Travel Time Tomography in the South-Central Andes (32-35°S): Implications for Regional Tectonics

In the South-Central Andes, the crustal structures driving the tectonic evolution of the Andean Cordillera remain unresolved. So far, most seismological studies focused on the subduction interface, leaving crustal seismicity and its relationship with crustal deformation and Andean volcanism mostly unconstrained. However, because of their large number compared to higher magnitude events, the characterization of small-magnitude crustal earthquakes is key to identify active structures and better constrain the tectonic models. In this work, we exploit 53 months of continuously recorded, three-component waveforms from the permanent seismic network in central Chile using a deep-learning approach to improve the detection of small-magnitude earthquakes. To increase station coverage, we also use the seismic phases obtained from a previous temporary seismic deployment. We use the obtained seismicity catalog to refine tomographic models of that region, revealing a more detailed architecture of the Chilean forearc. Travel times calculated in the new 3-D velocity model allowed us to locate similar to 14,000 earthquakes. Refined double-difference relocations of similar to 4,900 events located beneath the West Andean Thrust suggest a large-scale, west-dipping structure which, together with the west-verging tectonic front, likely contributed to the uplift and crustal deformation during the past similar to 20 Myr.

Automated summary

In this study, a deep-learning approach is used to improve the detection of small-magnitude earthquakes in the South-Central Andes. The refined seismicity catalog aids in refining tomographic models and revealing a more detailed architecture of the Chilean forearc. The double-difference relocations of seismic events suggest a large-scale, west-dipping structure beneath the West Andean Thrust, contributing to crustal deformation and uplift over the past 20 million years.