Integrating geophysical and geological analyses to clarify the tectonics of the Isthmus of Tehuantepec, Mexico

The Isthmus of Tehuantepec constitutes a geodynamically critical segment of the circum-Pacific belt, characterized by pronounced structural heterogeneity and complex plate interactions. The principal objective of this investigation is to delineate the crustal framework of the Isthmus of Tehuantepec and to examine the potential development of a diffuse triple-junction zone accommodating the interactions among the North American, Cocos, and Caribbean plates. To this end, satellite-derived gravity models (EIGEN-6C4), regional aeromagnetic data (NA_Mag), and twenty years of seismic records from the Mexican National Seismological Service (SSN) were integrated. Derivative filtering of potential-field data, Bouguer anomaly and vertical-derivative analyses, and a three-dimensional gravity inversion were performed. The results reveal a prominent low-density feature (Z1) offshore Santo Domingo de Tehuantepec, coinciding with magnetic minima and an abrupt (∼90°) rotation in the alignment of shallow seismicity. This feature is interpreted as a lithospheric weakness or slab tear associated with the oblique impingement of the Tehuantepec Ridge upon the Middle America Trench. The integrated geophysical evidence supports the interpretation of a segmented convergent margin, where deformation is accommodated within a distributed triple-junction zone rather than a single point.