Reply to the comment by R. A. Astini and F. M. Dávila on “The West Andean Thrust, the San Ramón Fault, and the seismic hazard for Santiago, Chile”

[1] We have proposed earlier a new tectonic model for the evolution of the Andes mountain belt as a bivergent orogen. Here, to reply to a comment by Astini and Davila [2010], we discuss briefly the protracted diachronic evolution (over tens of million years) by propagating deformation at the large‐ scale (over 10–10 km), its influence on basin formation in the back‐arc region (retroarc foreland basin), and the mechanical implications of the bivergence in the tectonics of the fore‐arc region, particularly the possible effects of the underthrusting of the coastal crustal‐scale rigid block (the Marginal Block) beneath the West Andean Thrust. [2] The comment by Astini and Davila [2010] criticizes our new model presented by Armijo et al. [2010] suggesting that theAndes is a fundamentally bivergent (or doubly vergent) orogen and defends the conventional model of Andean orogeny, which we think obsolete, involving crustal shortening only by development of retroarc thrusts in the back‐arc region (e.g., as discussed, among many others, by Isacks [1988]). Our model is based on the structural study of the San Ramon Fault system and the Principal Cordillera at the front of the western flank of the Andes, which is used to characterize the crustal‐scale West Andean Thrust (WAT), a major fold‐thrust system in the fore‐arc region, synthetic to the subduction zone. Astini and Davila raise cursorily a large number of important questions, which cannot be fully addressed in this reply. [3] To summarize the main argument: (1) Astini and Davila think that according to the critical taper wedge model [e.g., Davis et al., 1983], the dominant thrusting of the Andes cannot have shifted from an initial westward vergence to an eastward vergence, as we propose; (2) they claim that the well‐known eastward (cratonward) migration of thrusting associated with foreland basin formation in Argentina cannot be explained if the initial dominant thrusting of the Andes was in the fore arc, with westward directed vergence; and (3) Astini and Davila argue that no continental block in the fore‐arc region, as the Marginal (or Coastal) Block that we have defined, can be considered as a western foreland of the Andes because there is no well‐ developed western foreland basin. The miscellaneous final remarks by Astini and Davila express their doubts that our model may fit currently accepted models of mass transfer, sediment flow across orogens, and tectonic‐climatic forcing because according to our model, a major topographic slope would have been created to the west of the Andes (a feature that as anyone can check is not hypothetical, but a matter of fact). Last (but not least), the Andes at 33.5°S latitude would not be in an early stage of its evolution (as we claim) because sediments in the Argentinean foreland record its development since more than 20 Ma. Our reply, intended to identify first‐order conflicting issues, is as follows: