Intra-arc tectonic deformation around the Irazú–Turrialba volcanic complex, Costa Rica

The tectonic setting of the Irazú-Turrialba volcanic complex in central Costa Rica is characterised by a diverse tectonic interplay, including oblique subduction of the Cocos Plate beneath the Caribbean Plate and a diffuse region of deformation known as the Central Costa Rica Deformed Belt. The western (inferred) limits of this deformation region consist of the northwest propagation of a tectonic forearc sliver along the strike of the Central America Volcanic Arc. The eastern limit is attributed to the northeast escape of the overriding Panama Microplate. We exploit the recordings of a dedicated seismic network composed of 42 stations, operating from April 2018 to March 2019, to investigate this complex deformation associated with volcanic systems. Our local network improved the magnitude of completeness and allowed us to invert focal mechanisms that revealed the kinematics of tectonic and magmatic structures. We detected and located 967 local earthquakes, and constrained a new, local 1D velocity model for the investigated volcanic region. The relocated seismicity and associated focal mechanisms constrained for major earthquakes point out local crustal deformation, obliquely-orientated from the major regional tectonic blocks. We propose a conceptual geological model suggesting that deformation occurring at each volcano is subject to distinct tectonic regimes. In particular, we suggest that Irazú is sensitive to motion accumulated from the forearc sliver, while Turrialba is affected by the regional subduction.