jats:titleAbstract</jats:title>jats:pImaging and resolving the lateral continuity of 3‐D crustal structures enhance our ability to interpret seismicity and to understand how orogens are created. We apply a Bayesian, hierarchical inversion approach based on a transdimensional trees‐structured wavelet parameterization to recover phase velocity maps at 2–40 s periods. We then invert phase velocity dispersion to constrain a 3‐D shear velocity model of the crust beneath south‐central Iran. Together with accurate earthquake centroid depths and focal mechanisms, the pattern of 3‐D velocity variations supports recent suggestions that most large earthquakes in the Zagros occur within the lower sedimentary cover or close to the sediment‐basement interface. Furthermore, we find evidence for Arabian basement underthrusting beneath central Iran, although only in one location does it appear to generate earthquakes. Our new 3‐D tomographic model clarifies and throws new light on the crustal structure of the SE Zagros and its relation to seismicity and active faulting.</jats:p>