Low-frequency HVSR response across the northern Salado Basin, Argentina: first-order constraints on the impedance structure of the basin

The Salado Basin is a Late Mesozoic–Cenozoic intracratonic sedimentary basin developed over the Río de la Plata craton in eastern Argentina, with sedimentary fill exceeding 6 km in its main depocentral areas. Despite its regional significance, subsurface information across the onshore basin remains sparse, and no systematic ambient-noise study has previously been conducted within its limits. This work presents the first HVSR dataset within the Salado Basin, based on 19 sites distributed across a broadly NNW–SSE-oriented regional sampling framework extending from the shallower-basement domain north of the basin into the depocentral sector. The reference fundamental frequency decreases from approximately 0.3–0.5 Hz at the shallower-basement sites to ∼0.1–0.2 Hz in the depocentre, accompanied by a transition from simple, single-peak curves to broader, multi-peak responses. Exploratory full-curve clustering identifies two coherent families of HVSR morphology that align spatially with this pattern and with the regional gradient in compiled basement depth. At S01, where independent constraints indicate a basement depth of approximately 280–300 m, a first-order analysis yields an effective shear-wave velocity of ∼540–580 m/s, which is geologically plausible for the partially consolidated cover overlying the crystalline basement. In the depocentral sector, however, a sensitivity analysis shows that reproducing the compiled basement depths would require average shear-wave velocities that are difficult to reconcile with a plausible sedimentary fill. The lowest-frequency peak is therefore interpreted as more likely to reflect a major intra-basin impedance contrast, with the sediment–basement interface probably lying below the analysed frequency band. Secondary peaks are tentatively associated with shallower intra-basin contrasts. The dataset extends previous HVSR applications from the Río de la Plata coastal plain into the basin interior and provides a regional framework for future calibrated investigations.