Ambient noise tomography of the Popocatépetl volcano using the principal Green tensor components

A 3D shear wave velocity model of the subsurface of Popocatépetl volcano was obtained using ambient noise tomography, employing the principal cross-terms of the empirical Green’s function. Daily cross-correlation waveforms were computed from the data recorded by four seismic broadband stations in 2012. Dispersion curves were estimated from the stack of anti-causal and causal parts for the three ground motion components. In the period ranging between 0.5 and 7 s, the radial component provided the most well-defined group velocity dispersion curves for Rayleigh waves. Dispersion curves for long paths (> 9.5 km) suggested the presence of a layered structure with group velocity values ranging from 0.5 to 3.0 km/s. Dispersion curves for short paths (< 7 km) and close to the volcano showed values similar to those for long paths but with a velocity inversion occurring between 3- and 5-s periods. Despite the scarce ray-path coverage, a tomography inversion provided the means to image an S-wave velocity anomaly (2.5–3.0 km/s) in the northern part of the crater at depths not larger than 6 km. The volcano-tectonic seismicity during 2012–2013 was found to be concentrated in the southern segment of this anomaly, which seems to mark a boundary between a solidified body (possibly a product of ancient volcanic craters) and the softer material.