The transpressive southern termination of the Bucaramanga fault (Colombia): Insights from geological mapping, stress tensors, and fractal analysis

Abstract

This study provides a kinematic model of the southern termination of the Bucaramanga Fault (BF), in the Eastern Cordillera of Colombia, through the integration of geological information, field geology, morphostructural mapping, deduced stress tensors, and fractal analysis. Minor Riedel-type faults are related to the main fault trace and to its southern termination in multiple structures and allow a determination of the maximum horizontal stress (SHm) azimuth as between 105° and 140°, while stress tensors linked mainly with the southern ending faults show an SHm with an azimuth ranging from 108° to 169°. The southern termination of the BF comprises a series of sub-parallel faults that reach lengths of up to 60 km, and stress tensors solutions confirm the prevalence of pure strike-slip motion. This set of faults constitutes a transpressive system in a restraining bend (positive flower structure), characterized by a “domino” style, that captured the Boyacá and Soapaga faults, two of the inverted structures along the axial zone of the Eastern Cordillera. A general sinistral displacement of 23 km is assumed along the principal BF, which is distributed along the southern positive flower structure with kinematics that change from strike-slip in the centre to oblique-slip on the lateral faults. We performed fractal analysis and obtained a D-value of D = 1.42 ± 0.07 for the whole area, in contrast a value of D = 1.37 ± 0.08 for the northern part and D = 1.39 ± 0.12 for the southern part of the BF, and taking into account the standard deviations, our analysis corroborates the existence of similar faulting mechanisms and fractionation.