Could the Liqui&#241;e-Ofqui fault zone promote the 2011 Cordon Caulle eruption ?
Authors: Novoa Lizama Camila , Gerbault Muriel , Rémy Dominique , Cembrano José , Lara Luis , Tassara Andres , Hassani riad , Baez Juan Carlos , Ruz Javiera 
Published: March 2021

&lt;p&gt;The 2011-2012 Cordon-Caulle eruption&amp;#160;was the largest subaerial eruption&amp;#160;of&amp;#160;the 21th&amp;#160;century. An&amp;#160;inflation captured from InSAR between 2007 and 2009 was related to a volume of magma injection&amp;#160;too small to have&amp;#160;triggered&amp;#160;this eruption. Here, we benefit from SAR imagery acquired by ALOS-1, ENVISAT and SENTINEL-1 data,&amp;#160;to&amp;#160;analyze the temporal and spatial behavior of ground displacements&amp;#160;before, during and after the eruption. We find that a similar&amp;#160;prolate&amp;#160;spheroidal&amp;#160;source explains the data for the pre-eruptive&amp;#160;and post-eruptive periods.&amp;#160;Then&amp;#160;we explore two tectonically-related hypotheses to explain&amp;#160;the observed&amp;#160;displacements&amp;#160;during the explosive&amp;#160;phase&amp;#160;of the eruption. Therefore, first we model InSAR data using&amp;#160;standard&amp;#160;inversion&amp;#160;models&amp;#160;to evaluate&amp;#160;how&amp;#160;slip motion&amp;#160;along specific structures&amp;#160;explain&amp;#160;surface&amp;#160;observations.
Our&amp;#160;results&amp;#160;show&amp;#160;that the explosive phase's&amp;#160;ground displacements&amp;#160;could have been&amp;#160;produced&amp;#160;either&amp;#160;by&amp;#160;the&amp;#160;collapse&amp;#160;of the&amp;#160;caldera and&amp;#160;the&amp;#160;graben&amp;#160;overriding the&amp;#160;reservoir,&amp;#160;or by&amp;#160;slip motion&amp;#160;along a dextral-strike slip&amp;#160;fault&amp;#160;zone&amp;#160;related to the&amp;#160;North-South trending&amp;#160;Liqui&amp;#241;e-Ofqui fault zone. Second,&amp;#160;we&amp;#160;use&amp;#160;3D&amp;#160;numerical&amp;#160;models&amp;#160;and&amp;#160;elasto-plasticity&amp;#160;to&amp;#160;assess&amp;#160;the&amp;#160;failure conditions&amp;#160;along both structures&amp;#160;resulting from&amp;#160;an&amp;#160;overpressure applied at the wall of the&amp;#160;prolate-spheroidal&amp;#160;reservoir. Our results show that a magma
injection consistent with the&amp;#160;2007-2009&amp;#160; inflation signal&amp;#160;rather promotes constriction at the roof of the reservoir, which tends to impede fluid flow towards the surface. The presence of a relatively weak graben-caldera structure in our models show that this constrictional area is enhanced. On the other hand, the elasto-plastic pattern resulting from the application of a dextral-slip motion along the LOFZ branch-fault generates a&amp;#160;dilatational plastic zone that connects the reservoir wall to the surface, where it coincides with the location of the 2011 eruption.&amp;#160;Hence we propose that the LOFZ branch-fault, weakened during the pre-eruptive inflation phase, destabilized and slipped&amp;#160;two years later&amp;#160;in a way that&amp;#160;it&amp;#160;served&amp;#160;as&amp;#160;open&amp;#160;channels&amp;#160;for fluid&amp;#160;migration from the&amp;#160;magma&amp;#160;reservoir&amp;#160;up to the surface.&lt;/p&gt;