Tectonics and Sliver Motion in Costa Rica: Strain Partitioning Constrained by GNSS Velocities Data

The tectonic deformation of Costa Rica is controlled by the subduction of the Cocos Plate beneath the Caribbean Plate and the Panama microplate along the Middle America Trench, with oblique convergence in northern Costa Rica to 2024 from 154 permanent stations distributed across Costa Rica to derive for the first time spatially continuous velocity and strain‐rate fields in the forearc, arc and backarc using an interpolation approach adapted from the VISR method. Our results reveal that southeastern Costa Rica is dominated by trench‐normal convergence and high compressional strain rates, with negligible trench‐parallel motion, reflecting limited strain partitioning where convergence is nearly orthogonal to the trench. In contrast, northwestern Costa Rica exhibits pronounced trench‐parallel forearc motion that increases northwestward to between and plate‐convergence obliquity and possibly influenced by interplate coupling. Strain rate patterns further show, for the first time, that the Central Costa Rican Deformed Belt forms a broad kinematic transition zone characterized by low volumetric strain and distributed near‐isochoric deformation that accommodates differential motion between the Caribbean and Panama Plates. We further show that the Haciendas‐Chiripa Fault System accommodates a major fraction (between 63% and 83%) of the northwestward sliver motion, with an inferred dextral slip rate of and a locking depth of , extending sliver tectonics from the forearc to beyond the volcanic arc. Together, these results provide a unified kinematic framework for deformation in Costa Rica and clarify the mechanisms controlling strain partitioning at the southeastern termination of the Central American forearc sliver.