Deciphering the crustal structure of the Lerma Valley (NW Argentina): a multi-method seismic investigation

Abstract. We investigated the crustal structure beneath the Lerma Valley in northwestern Argentina using data from a local seismic network deployed between 2017 and 2018. This geologically complex transition zone between the Eastern Cordillera and the Santa Bárbara system is characterized by moderate to high seismicity, yet remains largely understudied despite its strategic location within the Andean orogen. Its passive orogenic setting and evidence of inherited structures make it a natural laboratory for exploring intraplate deformation and foreland basin evolution. We combined local and teleseismic receiver functions with ambient noise tomography (ANT), jointly inverting Rayleigh wave phase velocities to obtain 1D shear-wave velocity profiles. The results reveal a stratified crust with four main discontinuities at ∼53-43, 35–30, 10–8, and 1.5–1.2 km, corresponding to the Moho, mid- and lower-crustal boundaries, and the sedimentary basin base. A southward-dipping Moho is evident from CCP migration and T-component phase shifts. Velocity profiles also show a north–south contrast: lower velocities (1–2.5 km s−1) in the south indicate thicker, less consolidated sediments, while the north exhibits more competent crust (up to 3.5 km s−1). The final model comprises five layers, including three sedimentary and two crystalline crustal units. We also introduced a layer-dependent κ correction, revealing a trend from 1.65 at the Moho to 2 in the upper layers. These results provide new geophysical constraints on the crustal architecture and tectonic evolution of this underexplored Andean region.