Journal Article

Structural Characterization of the Taltal Segment in Northern Chile Between 22°S and 26°S Using Local Earthquake Tomography

Leon‐Rios, Sergio, Maksymowicz, Andrei, Rietbrock, Andreas, Reyes‐Wagner, Valentina, Comte, Diana, Calle‐Gardella, Daniela, Roecker, Steven

2024

Overview

Recordings of earthquakes by a temporary deployment of 84 short period seismometers in northern Chile were used to derive regional 3D seismic velocity models for the Taltal segment. We used the Regressive ESTimator (REST) package for event detection and automatic onset estimation of P‐ and S‐wave arrival times to create an earthquake catalog with 23,985 hypocenters. We followed standard acceptability criteria (i.e., azimuthal gap and residual cutoff) to create a high‐quality data set and inverted for 3D Vp, Vs and Vp/Vs models using local earthquake tomography. Plots of hypocenters from the catalog, comprising 16,349 earthquakes, reveal active structures in the upper crust, dip changes along the slab and fracturing within the oceanic crust. Moreover, the wavespeed models illuminate anomalies in both the Nazca and South American plates that correlate with the observed seismicity distribution, including variations from low (1.75) to high (>1.80) Vp/Vs near the Atacama fault system on the coastline and the Domeyko Fault System in the forearc. The seismic velocity models also provide evidence for fluid circulation caused by the subducting Taltal ridge on the coast and partial melting feeding a volcanic complex close to the Andes. Finally, the observed low Vp/Vs ratios (∼1.75) are associated with copper mining operations in the area, suggesting that this kind of imaging can be used to characterize the distribution of potential ore deposits in the area. Plain Language Summary We recorded earthquakes in northern Chile with a network of 84 seismometers and used the arrival times of P and S waves to generate 3D wavespeed models of the region. These models reveal several structures in the area, including changes in the angle of the subducting Nazca plate and fractures in the oceanic crust. Among features observed in both the Nazca and South American plates are the Atacama and Domeyko fault systems. We also infer fluid circulation caused by the subducting Taltal ridge and partial melting that feeds a volcanic complex near the Andes. Low values of the Vp/Vs ratio are associated with copper mining operations in the area and could be used to identify new ore deposits. Key Points Seismic catalog reveals forearc activity and slab dip variations. Vp anomalies in the oceanic plate are related to mid‐depth seismic events Velocity models uncover anomalies in Salar de Atacama and Taltal ridge that might influence seismicity distribution and hydration changes Shallow low Vp/Vs (<1.75) correlate with ore deposits; deep high Vp/Vs (>1.80) suggest fluids and melting for the Lastarria volcanic complex

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: 3D velocity models / Catalogues / continental forearc / Copper / Earthquakes / local earthquake tomography / Melting / northern Chile / Oceanic crust / Plates / Seismic activity / seismic catalog / Seismic velocities / Seismicity / Seismometers / tectonic processes / Tomography