Linking Environmental Controls to Seismicity at Ojos del Salado Volcano

The Ojos del Salado volcano is the highest active volcano in the world, located in the southern Puna Plateau in the high Andes, and at the southern end of the Central Andean Volcanic Zone. Ojos del Salado has erupted in the Holocene and appears to be geothermally active as it is the most likely source of the hot springs that feed into the nearby Laguna Verde. Despite the Ojos del Salado’s size and recent activity, it is not closely monitored and little is known about the current state of this quiet giant. To remedy this, we deployed a passive network of 29 geophones on the flanks of Ojos del Salado and down to the Laguna Verde to record seismic activity at and near the volcano for the month of February, 2024. This data provides insight into the level of seismic activity, and from this we can draw some conclusions about the volcanic activity present at Ojos. We used machine learning techniques to detect events, these were then manually checked and compiled into a SEISAN catalogue. Initially 345 local events and 129 regional events were detected. Taking only events that were recorded on at least eight stations and could be relocated within the network we found that there remained 152 local events within the network. These relocated events formed two main clusters, one on the western flank of the summit and one just north of the summit, between the Laguna Verde and the Ojos del Salado. The magnitude of completeness of this relocated catalogue was -0.3ML, and the local magnitudes ranged from -1ML to 2.8ML. The locations and fault plane solutions of the events at the summit suggest north south extension and generally follow mapped faults in the area, and agree with the main regional stress axes. The smaller cluster just north of the volcano are oriented differently, we suggest that this cluster, which mainly occurred as a swarm on February 8th following two days of heavy rainfall, may be due to stresses caused by an increase in geothermal fluids supplied in part by the heavy rains joining the geothermal system and increasing the local pore pressure. The passive data collection has also allowed us to analyze the continuous seismic signal which shows a periodicity of 12 hours and 24 hours in frequency bands from 1 to 10Hz. This could be an indication of the effect of solid earth tides, temperature, or even rainfall on the seismicity at the Ojos del Salado volcano.