Seismic evidence of the active regional tectonic faults and the Copahue volcano, at Caviahue Caldera, Argentina

Abstract

Understanding interactions between tectonic faults and a nearby active volcano is often realized by combining seismic and field observations. A good example of such an interaction is the Caviahue caldera. It is located in an intra-arc extensional pull-apart basin, within a transition zone joining the northern part of the right-lateral strike-slip Liquiñe-Ofqui Fault System and the thrustfault Antiñir-Copahue fault zone. Most of the active volcanoes in South Chile are related to the Liquiñe-Ofqui Fault System. Some faults located inside the Caviahue caldera were described with reverse mechanisms by some studies whereas they were found to be normal by others. In order to discriminate the actual focal mechanisms, two seismic clusters that occurred in 2017 and 2018 inside the Caviahue rectangular caldera, close to the active Copahue volcano, were studied. Earthquakes (520) were located; focal mechanisms (56) were determined from which an average seismic moment tensor was calculated. The locations and focal mechanisms of the earthquakes allow splitting the seismicity into two main regions, one of tectonic origin (with strike-slip faults) and another one of volcanic origin (with normal faults). The first seismic cluster is located close to Caviahue village, with strikeslip focal mechanisms, in an NNE direction as the nearby Liquiñe-Ofqui Fault strikes. The other part of the seismicity is located close to the northeastern structures of Copahue volcano, in the hydrothermal zone of Anfiteatro, Termas de Copahue, and Maquinitas. It is oriented in an NE direction and is composed of earthquakes with normal focal mechanisms, not reverse as postulated in past studies. The active Copahue volcano lies in the SW prolongation of these normal faults, in agreement with the tectonics of the Caviahue caldera. Then, the two nearby seismic clusters reveal both a tectonic origin, with strike-slip focal mechanisms compatible with the Liquiñe-Ofqui Fault System, and a hydrothermal origin with normal focal mechanisms, compatible with the hydrothermal system of the Copahue active volcano.

Seismic Event Detection in the Copahue Volcano Based on Machine Learning: Towards an On-the-Edge Implementation

“…In this study, we focused on the seismic traces recorded at the HIGI station, since more tectonic events were found in proximity to HIGI, and structural models suggested that the magmatic chamber was also situated to the east of the volcanic cone. Moreover, the data quality of the HIGI station was superior to that of TERM, which was possibly due to the presence of geothermal emanations causing noise [35]. Installed at coordinates 37.851°S, 71.030°W and an elevation of 1637 m above sea level, it was situated in the old Hueney campsite.…”

“…Between December 2017 and March 2018, the National University of Río Negro deployed a temporary network (called CP) of six broadband and two short-period seismic stations [35]. CP covered an area of 12 km in the East-West (E-W) direction and 14 km in the North-South (N-S) direction in Caldera del Agrio.…”

“…The stations were strategically located in quiet areas during a period when there were very few people residing in the region. For the study presented in this paper, the seismological station that performed best according to the approach proposed in [35] was selected.…”

“…These files were in the MSEED format (used in seismology to store and distribute timeseries data from seismic instrument waveforms), and each was 24 h long, composed of 8,460,000 samples. Data quality was evaluated in [35], where the noise levels at each station were juxtaposed with Peterson's global seismic noise models by performing the initial removal of the instrument response. On the other side, the noise levels in all stations remained within the anticipated normal range when no seismic activity was present, as described in [36].…”

Long-duration seismicity and their relation to Copahue volcano unrest

“…A fault-controlled geothermal system located 4 km to the NW of Caviahue town (Fig. 1) (Lamberti et al 2019;Barcelona et al 2019) has shown to be seismically active, producing both volcano-tectonic events (Montenegro et al 2021) and volcanic tremors (Ibañez et al 2008;Melchor et al 2020).…”