Review of Best Practices to Calculate the Fundamental Frequency of a Site Based on H/V Spectral Ratio: Case Study of Garner Valley Downhole Array

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

The use of horizontal-to-vertical (H/V) spectral ratio method to study local site effects has grown due to its simplicity and the fact that simultaneous rock outcrop recording is not required. It is a widely accepted notion that the lowest frequency among the significant H/V spectral ratio peaks corresponds to the fundamental frequency (f₀) of the site. There are various approaches to obtain the H/V spectral ratio, each of which has pros and cons. In this study, a review of available methodologies is presented, followed by discussions on best practices to estimate the fundamental frequency of a site using ground motions recorded at the well-documented Garner Valley Downhole Array (GVDA). One discussion topic is combining two horizontal components of as-recorded motions. Three considered approaches to combine them are (1) use of complex number method, (2) geometric mean of the acceleration response or Fourier Amplitude Spectra and (3) calculate RotD50 (median spectral acceleration over all orientations). An advantage of the latter approach is that the final calculated horizontal component becomes independent of the orientation of recorded motions in the field. Furthermore, this study discusses different spectral calculation methods such as the 5% damped pseudo-acceleration response and Fourier Amplitude Spectra by presenting example results from GVDA. The application of smoothing techniques is another discussion topic and this study evaluates the use of the popular Konno-Ohmachi method and its consequences to shift the value of fundamental frequency. Overall, this study intends to review and discuss different practices to calculate the fundamental frequency using the H/V method using recorded data at GVDA.

Presenting Author: Ramin Motamed

Authors