Horizontal and vertical deformation rates linked to the Magallanes‐Fagnano Fault, Tierra del Fuego: Reconciling geological and geodetic observations by modeling the current seismic cycle

Abstract

We integrate geodetic, geological and seismological observations in Tierra del Fuego,into a consistent and quantitative analysis, to better understand the current crustaldeformation associated to the Magallanes-Fagnano Fault, i.e., the transform boundarybetween the South American and Scotia plates at the southern tip of Patagonia. Toobtain reliable geodetic estimates of the thickness of the seismogenic layer, we modelthe current seismic cycle from the great 1949 Mw 7.7 earthquake to the present,including the lasting effects of postseismic relaxation. The model parameters are con-strained by GNSS velocities obtained by reprocessing 24 years of observations in theisland with up-to-date models and satellite products. We combine the observed de-formation rates with long-term geological estimates of the slip rate in this transformsystem during the Holocene. The modeling results point to a seismogenic layer thick-ness of 15 ± 3 km and to fault planes inclined 63◦ ± 4◦ , dipping to the South. Alongthe sections of the Magallanes-Fagnano Fault in the island these results are consistentwith a seismic moment deficit rate, per unit of length, of 3.2±0.8×1012 N m a−1 km−1,and a cumulative seismic moment, to date, equivalent to an earthquake of magnitudeMw ´7. The postseismic viscoelastic relaxation, probably related to viscous flow inthe mantle, affects the entire region up to ∼ 200 km away from the Magallanes-FagnanoFault, and more than 60 years after the earthquake.