P-, S-wave velocity and VP/VS of the Colima Volcanic Complex from local earthquake tomography

The Colima Volcanic Complex (CVC), located in western Mexico, is a complex tectonic area dominated by subduction processes and the deformation and fragmentation of the continental plate. The CVC is characterized by three volcanic structures formed during successive periods of different dynamic and magmatic processes. Several studies have been performed; however, the exact mechanism controlling the internal structure of the CVC is still debated. Therefore, the purpose of this study was to estimate high-resolution P-wave velocity (V-P), S-wave velocity (V-S), and V-P/V-S models to gain new insights into the internal structure of the CVC. To do this, I used P- and S-waves travel times of 383 earthquakes recorded by the Mapping the Rivera Subduction Zone and the Colima Volcano Deep Seismic Experiment. The fast-marching method was implemented to solve the forward problem of travel time prediction and a subspace inversion-gradient-based technique. The robustness of the tomographic results was then assessed through checkerboard and restoring resolution tests. At the southwest of the CVC, approximately at 7-km depth, the resulting models showed a low V-P anomaly with an elliptical shape and a northeast-southwest trend, a low V-S anomaly with an irregular-shape of interconnected lobes, and high V-P/V-S with a similar pattern as the S-wave velocity model but confined to the Central Colima Graben. From the resulting tomographic images, I infer: (i) the presence of a shallow, complex system of magmatic reservoirs; (ii) that the southward migration of volcanic activity as an ongoing process; and (iii) the existence of compositional distinct magma reservoirs.