The West Andean Thrust, the San Ramón Fault, and the seismic hazard for Santiago, ChileReportar como inadecuado

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The importance of west verging structures at thewestern flank of the Andes, parallel to the subductionzone, appears currently minimized. This hampers ourunderstanding of the Andes‐Altiplano, one of the mostsignificant mountain belts on Earth. We analyze a keytectonic section of the Andes at latitude 33.5°S, wherethe belt is in an early stage of its evolution, with theaim of resolving the primary architecture of the orogen.We focus on the active fault propagation–fold system inthe Andean cover behind the San Ramón Fault, which iscritical for the seismic hazard in the city of Santiago andcrucial to decipher the structure of the West AndeanThrust WAT. The San Ramón Fault is a thrust rampat the front of a basal detachment with average slip rateof ∼0.4 mm-yr. Young scarps at various scales implyplausible seismic events up to Mw 7.4. The WAT stepsdown eastward from the San Ramón Fault, crossing12 km of Andean cover to root beneath the FrontalCordillera basement anticline, a range ∼5 km high and>700 km long. We propose a first‐order tectonic modelof the Andes involving an embryonic intracontinentalsubduction consistent with geological and geophysicalobservations. The stage of primary westward vergencewith dominance of the WAT at 33.5°S is evolving intoa doubly vergent configuration. A growth model forthe WAT‐Altiplano similar to the Himalaya‐Tibet isdeduced.Wesuggest that the intracontinental subductionat theWAT is amechanical substitute of a collision zone,rendering the Andean orogeny paradigm obsolete.

Autor: Armijo, Rolando; - Rauld, Rodrigo; - Thiele Cartagena, Ricardo; - Kausel Elicagaray, Edgar; - Vargas Easton, Víctor; - Campos, J



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