SUPPLEMENTING SHEAR WAVE VELOCITY PROFILE DATABASE WITH MICROTREMOR-BASED H/V SPECTRAL RATIOS

Frequency-dependent horizontal-to-vertical spectral ratios (HVSR) can provide information on one or more site resonant frequencies and relative levels of amplification at those frequencies. Such information is potentially useful for predicting site amplification but is not present in site databases that have been developed over the last 15–20 years for the Next-Generation Attenuation (NGA) projects, which instead use the time-averaged shear-wave velocity (VS) in the upper 30 m of the site (VS30) as the primary site parameter and are supplemented with basin depth terms where available. In order for HVSR-based parameters to be used in future versions of site databases, a publicly accessible repository of this information is needed. We adapt a relational database developed to archive and disseminate VS data to also include HVSR. Our intent with the database is to provide relevant HVSR data and supporting metadata, but not parameters derived from the data. We consider the relevant data to be the frequency-dependent HVSR, where the horizontal is taken as the median component and as a function of horizontal azimuth (referred to as polar plots). Relevant metadata includes site location information, details about the equipment used to make the measurements, and processing details related to windowing, anti-trigger routines, and filtering. We describe the database schema developed to organize and present this information. The relational database stores HVSR data, but not site parameters derived from the data. Site parameters of potential interest for modeling purposes include: (1) a binary variable indicating whether an HVSR plot contains a peak; (2) one or more peak frequencies; (3) peak amplitudes; and (4) peak widths. We describe and illustrate analysis routines to derive these parameters that are implemented in Python on a Jupyter Notebook enabled by DesignSafe-CI. These routines interact with the database via cloud computing, but are not directly part of the database.