Breaking the Caribbean Plate: Subduction Initiation Beneath the Northern Margin of Panama

Abstract The initiation of subduction zones is a poorly understood but core plate tectonic process. One unknown is how and under what conditions previously contiguous plates break. Here we present a comprehensive assessment of the Northern Panama Subduction Zone (NPSZ) where the Caribbean Plate is subducting to the SSW beneath Panama. Because the Panama arc was built onto the Caribbean Plate, the existence of the NPSZ means that the Caribbean Plate must have broken. The significant crustal thickness (∼20 km) and age (>90 Ma) of the Caribbean Plate make the NPSZ the closest analog to passive margin failure known. We use evidence from the 25 May 2023 Mw 6.5 megathrust earthquake northeast of Panama included in a newly refined earthquake catalog to identify the geometry of the downgoing plate. We combine these with plate reconstructions to study the initiation of the NPSZ, its subsequent evolution, and its tectonic implications.