The Planchón-Peteroa Volcanic Complex (PPVC) is located in the Central Andes, Argentina-Chile. Even though this active volcanic system is considered one of the most dangerous volcanoes in the region, with more than twenty modest (VEI < 4) Holocene eruptions, knowledge of its subsurface structures, internal processes, dynamics, and their relation, is still limited. Seismic interferometry (SI) is a high-resolution technique based on analyses of the interference of the propagation seismic energy at one or many stations. SI can be used to characterize the subsurface properties of a target area. In particular, previous SI studies performed in the area of the PPVC describe specific ranges of depth; therefore, more information is required for a thorough description of the subsurface features in the area and for a better understanding of the PPVC dynamics. We apply SI based on autocorrelations of selected regional and teleseismic events to image the subsurface structures below stations located in Argentina and Chile during 2012. The selection of the events is performed according to their location, magnitude, angle of incidence of P-wave seismic energy, and signal-to-noise ratio in the records. For each station, we extract time windows and we process them using two ranges of frequency, which are sensitive to different depth ranges. This work describes depths and zones previously not analyzed in the area using SI methods. The results not only complement the available geological, geochemical, and geophysical information, but present new information for depths between 10 and ~750 km depth, increasing the general knowledge of the subsurface features in the PPVC. Finally, we also propose a model for the subsurface down to the Moho, which indicates the crustal structure and the likely distribution of magma bodies in depth.@en

We applied the seismic interferometry technique to characterize the subsurface velocities of the Planchón-Peteroa Volcanic Complex, Argentina-Chile, down to a depth of about 350 m. Ambient seismic noise data were recorded by an array of six stations deployed in the eastern flank of the current active volcano of this volcanic complex—the Peteroa. To ensure retrieval of accurate surface-wave Green’s functions, we analyzed the directivity of the recorded ambient noise and then selected the noise windows containing source directions in line with the stationary-phase area for each station pair. Then, we obtained dispersion curves and further utilized them for the estimation of the S-wave velocity profile for the area enclosed by the stations. We inferred two layers above the investigation depth limit. In the first 70 m, a lowvelocity layer (300–400 m=s) is present, which is followed by a higher velocity layer (450–570 m=s) down to, at minimum, a depth of about 350 m. Higher velocities are observed at the northeast and the very southwest of the area under investigation, and lower velocities are observed between these areas. The S-wave velocity structure is consistent with the known near-surface lithologies of the area. The results along the western side of the area corroborate previous results obtained from geochemical studies. Velocity variations in the area are potentially caused by changes in lithology, porosity, and water saturation. This work contributes to the understanding of the subsurface of Peteroa volcano and provides useful information to the authorities for decision- making. Furthermore, these results are expected to be used by studies preceding risk analysis and hazard-assessment investigations. @en

Seismic interferometry (SI) retrieves virtual seismic signals from measurements at two receivers from surrounding sources. Studies have demonstrated that SI can image subsurface reflectivity. Claerbout (1968) showed that the reflection response can be obtained by autocorrelating the transmission response assuming a 1-D acoustic medium. Migration techniques using primary and multiple reflections in the autocorrelogram effectively imaged the subsurface structure (Schuster et al., 2003; Yu et al., 2003). This research aims to contribute to the knowledge of the subsurface structure at Planchón-Peteroa Volcano Complex (PPVC) by using SI. Inspired by the theory and applications in Wapenaar (2003) and Ruigrok and Wapenaar (2012), this work applies SI to fracture seismicity originated at PPVC or in active geologic faults located nearby this volcanic complex. Autocorrelating an extracted time window for selected events, zero-offset reflection responses were retrieved for each station. This response is further used to image shallow subsurface reflectors underneath each station. This application uses seismic data recorded by stations deployed in Argentina and Chile. The Argentine data was recorded by a temporary array of six 2-Hz 3-component stations deployed in 2012 on the eastern flank of the volcano. The Chilean data is provided by OVDAS-SERNAGEOMIN (South Andes Volcanic Observatory, Chile). OVDAS has a permanent array of six 30-seconds 3-component stations. Three of these stations recorded data simultaneously with the Argentine stations and were used for this research. Very local seismicity is required for this study, therefore event selection procedure is of great importance. The two arrays were initially used independently to locate fracture events (Casas, 2014; RAV-SERNAGEOMIN, 2012). In order to obtain accurate locations, the two datasets were used together to relocate the detected events (Casas et al., 2016; Olivera Craig et al., 2016). This preprocessing step enhances the resolution of the subsurface images obtained by application of SI at PPVC since appropriate wave paths are selected for processing @en