Shallow S-Wave Velocity Structure from Ambient Seismic Noise at Planchón-Peteroa Volcanic Complex, Argentina-Chile

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.