cuador and southwest (SW) Colombia suffered widespread damage during the twentieth century as a result of some of the greatest subduction earthquakes and associated tsunamis ever recorded. In 1906, the Ecuador‐SW Columbia margin, located at the transition between the continent and deep ocean, ruptured over a 500‐kilometer length as a single great (Mw = 8.8) subduction earthquake (Figure 1a) [Kelleher, 1972]. The 1906 rupture zone was partially reactivated in 1942, 1958, and 1979 by earthquakes of Mw 7.7 to 8.2 (Figure 1b), with 100‐200 kilometerlong rupture zones [Beck and Ruff, 1984].

Such considerable variation in earthquake rupture length and magnitude in this area's seismic cycles during the last century has raised questions about the nature and enduring significance of the boundaries that exist between rupture zones and about the long‐term recurrence interval between earthquakes.