Seismic interpretation has been used to provide crystalline basement estimates where drillhole stratigraphy is limited or unavailable. The base of a sedimentary basin unconformity is picked at the base of seismic facies characteristic of a sedimentary succession. The horizon is a high amplitude reflection in part, and can be irregular as is characteristic of an erosion surface. The seismic data below the base of a sedimentary basin unconformity horizon is noisy and reflection free, as is characteristic of highly deformed metamorphic and igneous rocks. To enable estimation of basement depths by this method, a checkshot survey is acquired from a deep drillhole within a given basin. A checkshot-generated time versus depth curve is used to depth-convert the time-domain base of a sedimentary unconformity horizon into a depth horizon.