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.

Earthquakes have been observed to rupture in segments. A good understanding of rupture segmentation is important to characterize fault geometries at depth for follow-up tectonic, stress-field or other analyses. Earthquakes with magnitudes Mw<7 are however often modeled with simple source models. We propose a data-driven strategy and develop pre-optimization methods for a segmentation-sensitive source modeling analysis. The first method we develop is a time-domain, multi-array backprojection of teleseismic data to infer the spatio-temporal evolution of the rupture, including a potential occurrence of rupture segmentation. We calibrate the backprojection using empirical traveltime corrections and we provide robust precision estimates based on bootstrapping of the travel-time models and array weights. Secondly we apply image analysis methods on InSAR surface displacement maps to infer modeling constraints on rupture characteristics (e.g. strike and length) and the number of potential segments. Both methods can provide model-independent constraints on fault location, dimension, orientation and rupture timing, applicable to form prior probabilities of model parameters before modeling. We use the model-independent constrains delivered by these two newly developed methods to inform a kinematic earthquake source optimization about parameter prior probability estimates. We demonstrate and test our methods based on synthetic tests and an application to the 25.11.2016 Muji Mw 6.6 earthquake. Our results indicate segmentation and bilateral rupturing for the 2016 Muji earthquake. The results of the backprojection using high-frequency filtered teleseismic wavforms in particular shows the capability to illuminate the rupture history with the potential to resolve the start and stop phases of individual fault segments.