2026/07/29 by Javier Fernández-Carabantes, Flor de Lis Mancilla, José Ángel López-Comino +3
paper · doi:10.1785/0220260043
Abstract The single-station microtremor horizontal-to-vertical spectral ratio (mHVSR) technique is commonly employed as a useful tool for seismic zoning, seismic site response, or structural studies at a local scale. In this study, we investigate its applicability at a regional scale by analyzing the structure of the Neogene–Quaternary sedimentary basin of the Guadalquivir River in southern Spain. This technique is applied at 50 stations from permanent and temporary accelerograph and broadband seismometer networks over one week to ensure the stability of the computed mHVSR curves. We obtain an interpolated map of soil resonance frequencies, which reflects low-frequency values and peaks with high amplitude in the sedimentary infill area, with a decreasing frequency trend in the northwest–southeast (SE) direction up to the outcrop of the olistostromic wedge. The presence of these complex chaotic structures acting as shallow resonators prevents the identification of the deep Paleozoic basement. Using data from boreholes and interpreted geophysical survey techniques, an empirical relationship between resonance frequency and basement depth for the basin is derived, as well as a simple shear-wave velocity model for the sedimentary infill. Our model reveals the existence of a generalized dip toward the SE that increases significantly toward the thrust belt of the Subbetic mountain range, reaching sediment thicknesses greater than 3500 m. Our results demonstrate the reliability of the methodology at a regional scale and are crucial for advancing seismic zoning and seismic response studies in the Guadalquivir sedimentary basin.