Sudden alteration in the seismic behavior of the Domuyo volcanic complex in the southern volcanic backarc zone, Argentina

The Domuyo volcanic complex (DVC) and its geothermal field in the retroarc zone of the southern Central Andes of Argentina present reduced seismicity according to different catalogs (USGS and INPRES). However, in 2015/ 2016, a local project was carried out in the area to describe its seismo-volcanic activity, registering a large number of volcano-tectonic (VT) events (538 VT). Considering there is scarce information on these events, this study focuses on analyzing the Domuyo Volcanic Complex (DVC) to assess its seismicity. Therefore, we installed a local seismological network in the study area and compared results with data registered by other authors. Four seismological networks were used, to obtain a more precise location of the seismic events and calculate the focal mechanisms of earthquakes with magnitudes greater than 2. For the first record of crustal seismicity detected by INPRES the September 10th, 2016 with a Ml 3.3, we calculated the focal mechanism with two possible solutions: a thrust solution with a strike component and a favored normal solution with a strike component. Additionally, we relocated the largest event in the Domuyo region on March 27th, 2019, with a magnitude of 4.4 (NEIC - USGS) and focal mechanism with a normal solution and a small strike component, obtaining a shallower depth of 3.9 km instead of 10 km. The new seismological data used in this paper, correspond to September 10th 2016, and two different time periods, the first comprising continuous data from March to April 2019, when the largest registered earthquake occurred in the Domuyo region, and the second from December 2019 to January 2021. At these periods, registered seismicity had magnitudes Ml between 1.9 and 2.8, and focal depths between 1.8 and 5.2 km. Four of these events count with focal mechanisms with extensional and limited strike-slip components that are tentatively linked to the known neotectonic structures affecting the western slope of the DVC. This seismic sequence agrees with previous proposals in which degasification from a magmatic body at shallow depths constitutes the trigger factor.