Dense coverage of high-resolution topographic measurements from the Lunar Orbiter Laser Altimeter (LOLA) now allows for a global survey of the long-wavelength morphology of lunar grabens, with important implications for the geologic processes that form them. Comparing model ground displacements for grabens that arise solely from faulting, and from faulting involving a dike at depth, with topographic measurements across some of the most prominent and best-preserved grabens shows that many of them are underlain by a dike. Matching ground displacement models to topographic observations is the only way to detect, and also provide specific geometric information about, dikes too small to be resolved in available gravity and magnetic measurements, and thus allows for quantitative assessments of magma source depths and required magma overpressures. Dike-forming magmas are likely mantle derived, originating from depths greater than 20 km, with dike widths exceeding 100–500 m. Such dike geometric properties are only plausible if a mechanically weak lunar lithosphere was under extension at the time of dike emplacement.

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