T24C-03
Afterslip and Viscoelastic Relaxation Model Inferred from the Large Scale Postseismic Deformation Following the 2010 Mw 8,8 Maule Earthquake (Chile)

Tuesday, 15 December 2015: 16:30
304 (Moscone South)
Emilie Klein1, Luce Fleitout1, Christophe Vigny2 and Jean-Didier Garaud3, (1)Ecole Normale Supérieure Paris, Paris, France, (2)ENS/CNRS, Paris, France, (3)ONERA Châtillon, Châtillon Cedex, France
Abstract:
Postseismic deformation following the large subduction earthquake of Maule (Chile, Mw8.8, February 27th 2010) have been closely monitored with GPS from 70 km up to 2000 km away from the trench. They exhibit a behavior generally similar to that already observed after the Aceh and Tohoku-Oki earthquakes. Vertical uplift is observed on the volcanic arc and a moderate large scale subsidence is associated with sizeable horizontal deformation in the far-field (500-2000km from the trench). In addition, near-field data (70-200km from the trench) feature a rather complex deformation pattern.
A 3D FE code (Zebulon Zset) is used to relate these deformation to slip on the plate interface and relaxation in the mantle. The mesh features a spherical shell-portion from the core-mantle boundary to the Earth's surface, extending over more than 60 degrees in latitude and longitude. The overridding and subducting plates are elastic, and the asthenosphere is viscoelastic. A viscoelastic Low Viscosity Channel (LVC) is also introduced along the plate interface. Both the asthenosphere and the channel feature Burger's rheologies and we invert for their mechanical properties and geometrical characteristics simultaneously with the afterslip distribution. The horizontal deformation pattern requires relaxation both in i) the asthenosphere extending down to 270km, with a 'long-term' viscosity of the order of 4.8.1018 Pa.s and ii) in the channel, that has to extend from depth of 50 to 150 km with viscosities slightly below 1018 Pa.s, to fit well the vertical velocity pattern (intense and quick uplift over the Cordillera). Aseismic slip on the plate interface, at shallow depth, is necessary to explain all the characteristics of the near-field displacements. We then detect two main patches of high slip, one updip of the coseismic slip distribution in the northernmost part of the rupture zone, and the other one downdip, at the latitude of Constitucion (35°S). We finally study the temporel evolution of this slip distribution, together with its correlation with the aftershocks distribution.