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

We integrate geodetic, geological and seismological observations in Tierra del Fuego, into a consistent and quantitative analysis, to better understand the current crustal deformation associated to the Magallanes-Fagnano Fault, that is, the transform boundary between the South American and Scotia plates at the southern tip of Patagonia. To obtain reliable geodetic estimates of the thickness of the seismogenic layer, we model the current seismic cycle from the great 1949 M-w similar or equal to 7.7 earthquake to the present, including the lasting effects of postseismic relaxation. The model parameters are constrained by Global Navigation Satellite System velocities obtained by reprocessing 24 years of observations in the island with up-to-date models and satellite products. We combine the observed deformation rates with long-term geological estimates of the slip rate in this transform system during the Holocene. The modeling results point to a seismogenic layer thickness of 15 +/- 3 km and to fault planes inclined 63 degrees +/- 4 degrees, dipping to the South. Along the sections of the Magallanes-Fagnano Fault in the island these results are consistent with a seismic moment deficit rate, per unit of length, of 3.2 +/- 0.8 x 10(12) N m a(-1) km(-1), and a cumulative seismic moment, to date, equivalent to an earthquake of magnitude M-w similar or equal to 7. The postseismic viscoelastic relaxation, probably related to viscous flow in the mantle, affects the entire region up to similar to 200 km away from the Magallanes-Fagnano Fault, and more than 60 years after the earthquake.

Automated summary

This study integrates geodetic, geological, and seismological observations to quantitatively analyze the current crustal deformation associated with the Magallanes-Fagnano Fault. The results indicate a seismogenic layer thickness of around 15 km and fault planes inclined around 63 degrees, dipping to the South. The earthquake moment deficit rate along the fault in the island suggests a seismic moment equivalent to a magnitude 7 earthquake, with long-term postseismic relaxation extending over a large region.