Abstract

The diverse tectonic characteristics in northern Chile, with large megathrust earthquakes M>8.5; the long-term seismic gap; slow slip events, repeating earthquakes and seismic swarms; and large-scale fault systems extending up to 1000 km in the continental crust, offer a great opportunity to perform seismic experiments to better understand the subduction process in highly erosive margins. In particular, even though the Antofagasta region (22°S and 25°S) has a notable scientific attention, the past studies have put their focus mainly in the coastal areas affected by the M8.0 Antofagasta earthquake in 1995 and the M7.8 Tocopilla earthquake in 2007, leaving unattended the Taltal segment (25°S-27°S) and the processes in the overriding plate from the coastline to the volcanic arc. This area shows interesting features such as the subducting Taltal ridge; large-scale crustal faults; and a high rate of seismicity along the plate interface down to ~100-150 km and also at shallow depths in the overriding plate. By benefiting from a large temporary network of 88 short-period sensors from the KIT-AMTC Mobile Seismic Array that recorded the seismicity in the region between March and October 2020, we automatically detected local earthquakes using the Regressive ESTimator (REST) autopicker package. Subsequently, we performed a local earthquake tomography and derive 3D seismic velocity models for Vp, Vs and Vp/Vs for the Taltal segment to address three main questions: How do the bathymetric features coming from the oceanic plate interact with the subduction process and affect the regional seismotectonic? What are the in-depth extents of the long-scale structures observed at surface? and What is the role of the fluids coming from the oceanic plate in the seismotectonic of the upper crust? This work shows the preliminary results from the passive seismic experiment and the main findings so far.