The north Ecuador--south Colombia (NESC) margin has three transverse morphotectonic segments (the Manglares, Tumaco, and Patia segments), each with different tectonic and structural patterns. Following the 1906 subduction earthquake, the NESC margin has been the site of three megathrust events in 1942, 1958, and 1979 for which the rupture zones abut one another. We first investigated variations in heat flow derived from bottom simulating reflectors (BSR) observed along multichannel seismic lines sampling the three morphotectonic segments. Strong along-strike variations of the BSR-derived heat flow, just landward of the deformation front, suggest that each morphotectonic segment has a specific thermal regime. Finite element thermal models show that these variations are mainly produced by changes in the age and the dip of the oceanic plate and local hydrothermal cooling. We then examined the relationship between seismogenesis and thermal structure along the plate boundary. The updip limits of the 1942 and 1979 seismogenic zones, estimated from the aftershock area and rupture zone, reach the trench, where the temperature at the top of the subducting plate appears to be 50¿--60¿C. Between these events the seismogenic zone of the 1958 earthquake is restricted to a region landward of a prominent outer basement high where the temperature appears to be 100¿--120¿C. We propose that on the NESC margin the updip limit of the seismogenic zone is primarily controlled by low-temperature processes except for the 1958 event for which the seismogenic updip limit appears to be related to a structural feature in the upper plate.