Ground-motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremor

Abstract

The spectral ratio between horizontal and vertical components (H/V ratio) of microtremors measured at the ground surface has been used to estimate fundamental periods and amplification factors of a site, although this technique lacks theoretical background. The aim of this article is to formulate the H/V technique in terms of the characteristics of Rayleigh and Love waves, and to contribute to improve the technique. The improvement includes use of not only peaks but also troughs in the H/V ratio for reliable estimation of the period and use of a newly proposed smoothing function for better estimation of the amplification factor. The formulation leads to a simple formula for the amplification factor expressed with the H/V ratio. With microtremor data measured at 546 junior high schools in 23 wards of Tokyo, the improved technique is applied to mapping site periods and amplification factors in the area.

Stochastic Simulation of Strong Ground Motions From Two M > 5 Uttarakhand Earthquakes

“…This method nullifies the effect from the source and propagating medium, therefore endorsing the effect of local geological site conditions at a shallow level. Many studies like those by Oubaiche et al, 2016, Nakamura (1989, 2000, 2009, Konno andOhmachi (1998), andBonnefoy-Claudet et al (2008) have found a strong correlation between H/V and SH transfer function. The H/V ratio is used as a transfer function which provides the level of site amplification, but in a broader manner.…”

Stability Assessment and Geomorphological Evolution of Sea Natural Arches by Geophysical Measurement: The Case Study of Wied Il-Mielah Window (Gozo, Malta)

“…A 5% cosine taper was applied to each window, and the Fourier spectra were calculated. The spectra of each window were smoothed, using a Konno-Ohmachi window [53], fixing the parameter b to 40. Finally, the resulting HVSR, in the frequency range 0.5-40.0 Hz, was computed by estimating the logarithmic average of the spectral ratio obtained for each time window, selecting only the most stationary and excluding transients associated to very close sources.…”

Effects of Anthropic and Ambient Vibrations on Archaeological Sites: The Case of the Circus Maximus in Rome

“…A surface wave test was conducted to retrieve a reliable seismic characterization of the subsoil in terms of shear waves velocity Vs. For this purpose, a 57.5-m-long seismic adopted [36]. The spectral ratio curve was calculated between the two horizontal components and the vertical one, according to Nakamura's procedure.…”

“…Then, for each time window, the signal was cosine tapered (5%) and the Fourier spectrum was calculated within the 0.20 ÷ 20-Hz frequency interval. Smoothing was applied using the Konno-Ohmachi function, and a constant bandwidth coefficient "b" ranging from 25 to 35 was adopted [36]. The spectral ratio curve was calculated between the two horizontal components and the vertical one, according to Nakamura's procedure.…”