Deep characterization of the Santiago Basin using HVSR and cross-correlation of ambient seismic noise

• Time- and frequency-domain cross-correlation methods are proposed for basin scale studies.
• Rayleigh phase velocity dispersion curves are calculated from 0.1 to 8 Hz.
• Seismic ambient noise highly correlates in stations over stiff soil deposits of the Basin.
• Shear wave velocity profiles of Santiago gravels have a pronounced increase rate with depth.
• The impedance contrast between the Santiago gravels and the underlying bedrock is negligible.

Continuously recorded seismic ambient noise is used to investigate the intermediate and deep structure of the Santiago Basin for seismic site-response evaluation. Single-station H/V spectral ratios (HVSR) were used as a proxy to identify zones with high stiffness soils and low impedance contrast with the underlying bedrock, as a complement of available surface geology information. Frequency-domain cross-correlation of the vertical components of ambient noise were calculated and used to estimate phase velocity dispersion curves associated to station pairs over different soil deposits. In addition, noise correlation functions (NCFs) calculated from time-domain cross-correlation of the vertical seismic noise records were used to estimate group velocity dispersion curves and to verify results from the spectral method. Data processing from both methods resolves a frequency band between 0.1 and 8.0 Hz, a critical band for civil infrastructure that is difficult to determine with traditional local-scale passive surface wave methods. Station pairs with high signal correlation over stiff soils in the center, south, and east part of the basin, mainly associated to flat HVSR response, yielded robust phase velocity dispersion curves that vary approximately from 3.5 km/s at 0.1 Hz to 1 km/s at 4 Hz. Shear wave velocity profiles inverted from the dispersion curves show high average shear wave velocities that also have a pronounced increase rate with depth and a lack of clear soil-bedrock interface at depths predicted by available gravimetric data.