Teleseismic Radial Anisotropy Reveals a Sill‐Dominated Magma Reservoir Beneath the Valles Caldera, New Mexico

Abstract The Valles Caldera (VC), one of the largest Quaternary silicic calderas in North America, formed by explosive rhyolitic eruptions. Seismic studies suggest a crustal magmatic reservoir beneath the caldera with low‐velocity anomalies, but resolving the detailed geometry of localized melt requires constraints from seismic anisotropy. To image P‐wave velocity and radial anisotropy using dense nodal array data, we develop a teleseismic tomography method that integrates an eikonal solver with the adjoint‐state approach. Our results reveal a pronounced low‐velocity anomaly (>20% reduction) extending laterally across the resurgent dome and down to 15–20 km depth, consistent with a crustal magma chamber. We also identify a colocated zone showing a previously unrecognized pattern of strong positive P‐wave radial anisotropy (up to 8%) where horizontally polarized P‐waves travel faster than vertically polarized ones. This anisotropy indicates a laterally extensive magmatic sill complex and provides new constraints on magma distribution and reservoir architecture beneath the VC.