Carlos Herrera , Francisco Pasten-Araya , Leoncio Cabrera, Bertrand Potin, Efrain Rivera, Sergio Ruiz, Raul Madariaga, Eduardo Contreras-Reyes

We study the 2020 MW 6.8 Calama earthquake sequence that occurred within the subducting oceanic Nazca plate. The mainshock is modeled via waveform inversion using a dynamic rupture model, while detection and location techniques are used to better characterize its aftershock sequence. We analyze the local seismotectonic and thermal context of the subducting Nazca plate to understand the trigger mechanism of this earthquake and how it compares with other significant earthquakes in the vicinity. The stress drop and the related dynamic rupture parameters of the Calama mainshock are similar to those of the nearby 2007 MW 6.8 Michilla and 2015 MW 6.7 Jujuy inslab earthquakes, which occurred to the west (trenchwards) and to the east (under the back-arc) of the Calama earthquake, respectively. The sequences of these three events were located using a 3-D tomographic velocity model. While the Michilla earthquake sequence occurred within the oceanic crust at temperatures of ~250°C, the Calama sequence occurred within the upper oceanic mantle at ~350°C and exhibited a smaller aftershock productivity than Michilla. Additionally, the 3-D tomographic model shows intermediate Vp/Vs ratios in the region of the Calama earthquake. This indicates a less hydrated environment that would be responsible for the smaller aftershock productivity of the Calama earthquake.