The shallow three-dimensional structure of Volcán de Colima revealed by ambient seismic noise tomography

Volcán de Colima is one of the most active volcanoes in North America. Even so, it has a poorly constrained upper crustal structure. Here, we present the highest-resolution three-dimensional shear-wave velocity tomography to date of the volcano. We measured group velocity dispersion curves of Rayleigh and Love waves extracted from ambient seismic noise recorded on the Colima Volcanic Complex and regionalised them into 2-D velocity maps. Those were then locally inverted using a neighborhood algorithm to obtain accurate shear-velocity models down to 4 km below sea level. The resulting three-dimensional shear wave velocity model gives us a new insight into the internal structure of the volcano to specifically better understand the shallow magma storage and magmatic plumbing system and, in turn, how it can be placed in a wider geotectonic context. Our results highlight a network of deeply rooted NE-SW low velocity zones oriented along a local fault system. The southward orientation of this low-velocity anomaly also roughly aligns with the north-south trend of the volcanoes that compose the quaternary Colima Volcanic Complex and could be associated with the gradual trenchward shift of the magmatic front of the volcanic complex dating from the formation of the Cántaro Volcano. The low-velocity anomaly overlaps a negative radial anisotropy indicating that magma follows vertically oriented structures, such as interfingered dikes or faults and cracks with a substantial vertical component. The low velocity anomaly under Volcán de Colima contrasts with a distinct high-velocity anomaly under Nevado de Colima that highlights the difference between the former active system, filled with solidified dikes and sills, and the current one, associated with a network of fluid-filled dikes.