Tsunamigenic slope failure along the Middle America Trench in two tectonic settings

Slope failure along the Costa Rica convergent margin commonly results from steepening of the continental slope above underthrust relief on the subducting plate. The 50-km-wide prehistoric Nicoya Slump was a big event that was followed by small slides from its headwall. Estimated maximum wave height above the slide is 27 m. The headwall occurs along a tectonized and unstable zone that extends northwest. An expected great earthquake in the adjacent Nicoya seismic gap could trigger future tsunamigenic landslides along this zone. The central Nicaragua slope, where the 1992 tsunamigenic earthquake occurred, has failed from steepening by tectonic erosion and perhaps subducting relief. The steep middle slope displays several large slide scars, each of which had the potential to generate a 6–7-m-high wave. A relation between the youngest slide and the 1992 earthquake is uncertain. Principal causes of landslides off Middle America were tectonic steepening and elevated fluid pressure. A mid-slope tectonized zone off Costa Rica allowed detachment of a huge slump involving the entire lower slope to the plate boundary. It may pose a hazard during rupture of the Nicoya locked zone.