The Triple Junction of the North America, Cocos, and Caribbean Plates: Seismicity and tectonics

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Abstract
The triple junction of the North America, Cocos, and Caribbean plates is ambiguously defined, mainly because the North America‐Caribbean plate boundary does not clearly continue beyond its known surface trace (the Motagua fault zone) in western Guatemala to intersect the Middle America trench. Well‐located regional shallow earthquakes (h≤70 km) show that there is no intermediate or large‐magnitude seismic activity associated with a presumed extension of the North America‐Caribbean plate boundary to the west, beyond its well‐defined surface trace. There is, however, a clear zone of shallow seismic activity from the western section of the fault system through southern Mexico. Fault plane solutions for these events indicate a left‐lateral strike‐slip displacement, which is in good agreement with surface faulting. We suggest that these strike‐slip faults, together with the Salina Cruz fault in the isthmus of Tehuantepec, mark the boundaries of a broad zone of deformation in southern Mexico and northern central America which takes up the interactions of the three plates. In this sense, no single point constitutes the triple junction. The geologic record suggests that the Motagua fault zone developed because the westernmost portion of the Caribbean plate became locked against North America.

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