A lower mantle S-wave triplication with a Scd branch is easily observed beneath Central American and its lateral variations has been studied extensively. Attempts to model Scd depth variations with a phase boundary based on tomography predict smooth variations . Recently, Hutko et al. <2005> presents evidence of a sharper feature with a vertical step-like jump of over 50 km, for paths sampling the western edge of a fast lower mantle structure beneath the Cocos Plate. We present a similar type of very anomalous Scd waveforms sampling the edge further to the east. We are able to model these waveforms by adopting the phase-boundary model but enhancing the existing tomographic anomaly just above the velocity jump, which appears to be a folded-slab.