Although the Planchón-Peteroa Volcanic Complex (PPVC) has undergone many hazardous eruptions, only a small number of geological, geochemical, and geophysical studies have been performed to describe this active volcanic system. In order to characterize the subsurface structures present at the PPVC, we applied seismic interferometry to fracture seismicity originating in this volcanic complex and along active geologic faults located nearby. We utilized seismic data recorded by two arrays of stations deployed in Argentina and Chile. Nine of these stations (three in Chile and six in Argentina) recorded data simultaneously and were used for this application. Only seismic events with energy arriving (sub) vertically to the stations were chosen for processing. According to the magnitude and the location of the selected seismic events, relocated seismic sources were used for the Chilean stations while, for the Argentine stations, only seismic sources located near that array were used. We obtained seismic evidence of the location of the subsurface reflectors underneath each station using zero-offset reflection responses retrieved from seismic interferometry by autocorrelation of (time windows extracted from) the selected seismic events. Then, applying a comparative analysis between the seismic results and the available geological information, we imaged the shallow subsurface of the area enclosed by the Chilean stations, and also by the Argentine stations. The results are consistent with the available geological information, provide accurate depth values for several subsurface discontinuities, indicate areas of higher heterogeneity, and support the emplacement of a magma body at ∼4 km depth from the surface. This work shows the first application of a novel variation of seismic interferometry based on autocorrelations to local-earthquake data recorded in a volcanic area.@en

Obtaining detailed images of aseismic parts of subducting slabs remains a large challenge for understanding slab dynamics. Hypocenter mapping cannot be used for the purpose due to the absence of seismicity, whereas the use of receiver functions might be compromised by the presence of melt. Global tomography can be used to identify the presence of the slab, but it does not reveal the structure in detail. We have determined how detailed images can be obtained using global-phase seismic interferometry. The method provides high-resolution (<15km in depth) pseudo zero-offset (i.e., colocated source and receiver) reflection information. We have applied the method to aseismic zones of the Nazca slab in which initiation of possible slab tearing and plume decapitation was identified by global tomography and electrical conductivity, respectively. We have obtained an image of the Moho and the mantle and found an attenuated area in the image consistent with the presence of an aseismic dipping subducting slab. However, our interpretation was not unambiguous. The results confirmed that the method is useful for imaging aseismic transects of slabs.@en

We investigated the applicability of global phases (epicentral distances of ≥ 120° and ≥ 150°) for the H/V spectral ratio to identify the fundamental resonance frequency. We applied the method to delineate a part of Neuquén basin in Argentina without the need for active seismic sources. We obtained fairly identifiable fundamental resonance frequencies in the range 0.15 Hz to 2.5 Hz. Receiver-side resonances were pronounced by stacking the H/V spectral ratio over many earthquake recordings. By doing so, the same fundamental resonances were found by using different window (P and S-phases) as well as different epicentral distances (≥ 120° and ≥ 150°). Our result, assuming average velocity, shows identical features in comparison with both the Bouguer anomaly and the active seismic profile nearby, indicating that our method is reliable. The method we demonstrate here can be applied in the fields particularly when the seismic array of long-term purposes is available.

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