Abstract The Ecuadorian margin is a forearc‐arc system shaped by oceanic terrane accretion and Carnegie Ridge subduction, yet the accretion mechanism and ridge subduction extent remain poorly constrained. Using teleseismic P‐wave receiver functions from dense seismic arrays, we image velocity discontinuities within the overriding plate and subducting slab beneath Ecuador. We identify a laterally continuous discontinuity at ∼20–25 km depth across the forearc and two deeper discontinuities at ∼40 and ∼50 km depth beneath the volcanic arc, indicating heterogeneous overriding plate lithosphere associated with terrane accretion. We also image an ∼18–20 km thick layer interpreted as the Carnegie Ridge crust below the margin. This layer thins eastward to ∼8–12 km at ∼50–105 km inland from the coast, marking the eastward extent of subducting ridge. If correct, this suggests that Carnegie Ridge subduction began relatively recently (∼2.9–4.2 Ma). These observations provide new constraints on crustal accretion and ridge subduction along Ecuadorian margin.