The three-dimensional structure beneath the Popocatépetl volcano (Mexico) based on local earthquake seismic tomography

This paper presents a new seismic velocity model (P- and S-wave velocities and Vp/Vs ratio) beneath the Popocatépetl volcano to a depth of ~ 4 km below sea level (bsl). This model is based on the tomographic inversion of P- and S-wave arrival time data from earthquakes in the region of the volcano. These data were recorded by the 15 stations of a temporary seismic network that was deployed on the volcano in 1999 and 2000. The recording period was during a relatively quiet period between two strong eruptions, which occurred before and after the experiment. This period is characterized by low levels of volcano-related seismicity. Most of the recorded events occurred across an area much larger than the network. In this study, we conducted several synthetic tests, which validate the use of the out-of-network events to improve the resolution of the tomographic inversion beneath the stations. In the resulting model, we see that the main volcanic edifice is associated with high velocities that have a mushroom shape and that these high velocities are most prominent in the P-wave model. This feature may indicate the presence of overpressured solidified igneous rocks, which comprise the edifice of Popocatépetl. Below the summit of the volcano, we observe a prominent high Vp/Vs anomaly, which reaches a value of 1.9. This anomaly probably indicates the existence of cracks and pores filled with melts and fluids, and it may represent a fracture zone that serves as a conduit feeding the volcano. This model characterizes the interior structure of the Popocatépetl volcano prior to the strong September 2000 eruption, which occurred a few months after the termination of the experiment.