Seismotectonics of the thick-skinned Santa Bárbara System in
northwestern Argentina: implications for regional crustal rheology and
structure
Abstract
The Andean foreland is divided into morphotectonic provinces
characterized by diverse deformation styles and seismogenic behavior
partially stemming from distinct geological histories that preceded the
current phase of subduction. The transition between the high Andes and
the eastern foreland is exposed to numerous natural hazards and contains
critical economic infrastructure, yet we know relatively little about
regional active tectonics due to few geophysical investigations. Here we
use waveforms collected during a 15-month-long seismic network
deployment in the Santa Bárbara System (SBS) of northwest Argentina
following the 2015 Mw 5.7 El Galpón earthquake to determine the
distribution and magnitude of local earthquakes, obtain a regional 1D
seismic velocity model, and improve our overall understanding of SBS
neotectonics. Of the nearly 1200 recorded earthquakes,
~700 occurred in the crust with half of the moment
release associated with events deeper than 25 km. The depth extent of
seismicity supports the notion that the SBS upper and middle crust are
homogeneous and that the lower crust is composed of granulites. These
conditions likely formed during Paleozoic mountain building and Salta
Rift-related Cretaceous magmatism, which dehydrated the crust. We find
no clear indications that a shallow, low-angle detachment fault inferred
to have been active during Cretaceous rifting exerts a strong control on
modern deformation in contrast to the active décollement beneath the
adjacent fold-and-thrust belt of the Subandes to the north. It remains
unclear how active, inverted normal faults in the SBS shallow crust
connect to the deeper zones of seismicity.