Thermal segmentation of mid‐ocean ridge‐transform faults

3‐D finite element simulations are used to calculate thermal structures and mantle flow fields underlying mid‐ocean ridge‐transform faults (RTFs) composed of two fault segments separated by an orthogonal step over. Using fault lengths and slip rates, we derive an empirical scaling relation for the critical step over length ( LS˜), which marks the transition from predominantly horizontal to predominantly vertical mantle flow at the base of the lithosphere under a step over. Using the ratio of step over length (LS) to LS˜, we define three degrees of segmentation: first‐degree, corresponding to type I step overs ( LS/LS˜ ≥ 3); second‐degree, corresponding to type II step overs (1 ≤ LS/LS˜