Bedrock Depth and Shear Wave Velocity Profile Estimation through HVSR Measurements in the Paraguayan Oriental Region

Abstract

The horizontal to vertical spectral ratio (HVSR) passive seismic method consists in processing measurements of ambient noise performed in three perpendicular directions. The objective is to define the primary resonant frequency of the site and estimate its amplification characteristics, which can be deduced from visible peaks or troughs in the HVSR curves. The shape of HVSR curves depend on the interaction of waves with the interface between sediments and the formation bedrock and, hence, can be related to the bedrock depth through derived relationships. This work presents 4 study cases in the Paraguayan oriental region where HVSR of microtremors were obtained. Furthermore, the obtained HVSR curves are inverted to get approximate shear wave velocity profiles under the assumption of sub-vertically propagating P and S body waves. HVSR curves were calculated through Geopsy (Wathelet et al. 2020) and the inversion process was made through OpenHVSR (Bignardi et al. 2016), both open-source tools for ambient vibration processing. In general, the method proves to give sufficient accurate estimates of sediment thickness and stratigraphy in typical Paraguayan formations of the oriental region and presents the advantage of being an economical and fast survey option, especially for early stages in a geotechnical campaign

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