Kinematics of the active West Andean fold-and-thrust belt (Central Chile): structure and long-term shortening rate M. Riesner1, R. Lacassin1, M. Simoes1, R. Armijo1, R. Rauld 1, 2, * and G. Vargas2 1 Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Univ Paris Diderot, UMR 7154 CNRS, F-75005 Paris, France 2 Dept. de Geofísica, Facultad de Ciencias Físicas y Matemáticas, Universidad de Chile, Santiago, Chile. * Now at Xterrae, Of. 61 Hernando de Aguirre 194, Providencia, Santiago, Chile. Corresponding author: Magali Riesner (
[email protected]) Key Points: • 3D structural map and geological cross-section of the WAFTB east of Santiago. • Kinematics of deformation deduced from precise mapping of syn-tectonic Farellones formation. • Long-term shortening rate of 0.1-0.5 mm/yr, with possible deceleration by ~20 Ma. Abstract : West-verging thrusts, synthetic with the Nazca - South America subduction interface, have been recently discovered at the western front of the Andes. At ~33°30’S, the active San Ramón fault stands as the most frontal of these west-verging structures, and represents a major earthquake threat for Santiago, capital city of Chile. Here we elaborate a detailed 3D structural map and a precise cross-section of the West Andean fold-and-thrust belt based on field observations, satellite imagery and previous structural data, together with digital topography. We then reconstruct the evolution of this frontal belt using a trishear kinematic approach. Our reconstruction implies westward propagation of deformation with a total shortening of 9-15 km accumulated over the last 25 Myr. An overall long-term shortening rate of 0.1-0.5 mm/yr is deduced.