Abstract

GINER-ROBLES, Jorge Luis et al. Strain 3D analysis and kinematics of the Middle American Trench in the junction of the Rivera and Cocos plates with the North-American and Caribbean plates. Bol. Soc. Geol. Mex [online]. 2021, vol.73, n.2, 00013.  Epub Jan 31, 2022. ISSN 1405-3322.  https://doi.org/10.18268/bsgm2021v73n2a150121.

In this work, we propose a kinematic model based on the strain 3D spatial distribution from focal mechanism solutions of instrumental earthquakes located along the Middle American Trench, in the convergence zone of Rivera and Cocos plates with North-American and Caribbean tectonic plates. We have used more than 1300focal mechanisms of' earthquakes (M ≥ 5.5), from the Global Centroid-Moment-Tensor (CMT) online global program to perform a cluster analysis of the spatial distribution of the tectonic strain tensor (ey, ex, ez) and its shape (k'). Accordingly, we have applied the Right Dihedral Method to a population of geographically clusteredfocal mechanisms, as well as the Slip Method, based on the slip data on the theoretical fault plane, for determining the extensional, compressive, and strike-slip zones, in correspondence with the principal tectonic features. Furthermore, we have realized 14 depth pro/files across the Middle American Trench (MAT) of the shape of the strain tensor and ternary Kaverina diagrams for constraining the tectonic deformation and developing a 3D model of the kinematics in the region. This analysis depicts a zonation in relation with the changing subduction angle of the slab and an increase of the convergence rate towards the SE, resulting from the mechanical coupling of the subduction, and showing less thrust earthquakes at the Rivera-North American convergence zone than at the Cocos-North American one. The proposed 3D geometry is in good agreement with the spatial distribution of large earthquakes, the slab dip angle, the presence of mantle currents at a 100 km depth and the occurrence of normal-type earthquakes. This model could also account for the presence of anomalous earthquakes such as slow and silent earthquakes in the Guerrero Gap.

Keywords : focal mechanism; Inversion; strain tensor; k'; Mexico.