Seismicity along the Magallanes-Fagnano fault system

Abstract

The Magallanes-Fagnano fault (at ~51-56°S) is a continental NW-SE transform fault zone that marks the boundary between the South American Plate (north) and the Scotia Plate (South). In 1949, two crustal seismic events of estimated magnitude M > 7 were located in this area using teleseismic records. Although, this region is scarcely populated, such shallow seismicity could represent a considerable threat to the remote urban centers in this sector. The characterization of the local seismicity always lacked good quality records and permanent instrumentation. In the recent past years, permanent seismic stations (CSN and INPRES-CTBTO) were deployed in the Tierra del Fuego Island and Southern Patagonia, providing with continuous time, broadband records of waveform data. In order to obtain better insights about the local seismicity associated with the Magallanes-Fagnano fault, we jointly inverted teleseismic receiver functions with Rayleigh-wave dispersion data to build a calibrated velocity model for the study region. In parallel, we analyzed the continuous waveforms to automatically detect local earthquakes and locate them using our regional velocity model. Our results show: 1) Shallow seismic events distributed along the Magallanes-Fagnano fault. 2) Diffuse seismicity characterizing the South American crust, north of 53°S. Our observations suggest two mechanisms of crustal deformation. In the Tierra del Fuego Island the seismicity is mostly associated with the Magallanes-Fagnano fault system. In the Southern Patagonia, along the Patagonian Andes the seismicity would be mostly due to isostatic rebound following the retreat of the Patagonian Ice sheet.