Mapping discontinuities of Popocatépetl volcano, Mexico, using seismic noise autocorrelations

Popocatépetl is one of the most studied volcanoes in Mexico. Seismic tomography has been a useful tool for obtaining subsurface images and velocity models of the volcano using volcano-tectonic seismicity and ambient noise records. As part of the passive seismic studies, mapping seismic discontinuities is used to complement the seismic tomography studies and detect large impedance variations. In this study, we mapped seismic discontinuities using autocorrelations of seismic ambient noise recorded over 20, 30, and 100 days at 24 broadband seismic stations. The two-way travel times of positive and negative reflections were manually identified using bandpass-filtered strategies. Our observations are compared to a previously reported velocity model and revealed three clusters of reflections categorized by their polarity and depth. The shallow negative polarity cluster is located between 0 and 2 km above sea level (a.s.l.) and correlates with the boundary between older volcanic structures—such as Tlamacas, Ventorrillo, and Nexpayantla—and deeper consolidated materials, including paleo-volcanic flows that follow the regional topographic trend. The positive polarity cluster is located between 0 and 4 km b.s.l. and is associated with a previously mapped low-velocity zone related to limestone and metamorphic basement. The deep negative polarity cluster, situated between 4 and 8 km b.s.l., approximately delimits the upper boundary of a high-velocity zone, indicating a significant velocity increase. We interpreted this as dense magmatic material at depth, potentially with low gas content and confined by lithostatic pressure, which may have favored its accumulation at this depth. Therefore, our observations reinforce the presence of significant seismic anomalies previously reported.