Abstract Precise position and geometry of the subducted slab are crucial for deciphering subduction zone volcanism. This is particularly important in the southern Costa Rican subduction zone, where the Cocos Ridge subducted at ∼2–3 Ma, coincident with the uplift of the Talamanca Range but later than the arc volcanism cessation (∼5–8 Ma). Here, we apply a refined Dip Direction Searching method to teleseismic receiver function waveforms from 17 broadband stations in this region. A northeast‐dipping interface is imaged deep to ∼110 and ∼60 km in the northwest and southeast of the subduction zone, respectively, interpreted as the Moho of the Cocos slab that has possibly undergone tearing. A flat interface is identified at ∼40–60 km depth exclusively beneath the Talamanca Range, which is most likely the Moho of the Nazca plate that has stagnated there since ∼8 Ma, blocking melt upwelling and consequently stopping the arc volcanism.

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