TY  - JOUR
A1  - Zhu, Chuanbin
A1  - Pilz, Marco
A1  - Cotton, Fabrice Pierre
T1  - Evaluation of a novel application of earthquake HVSR in site-specific amplification estimation
JF  - Soil dynamics and earthquake engineering
N2  - Ground response analyses (GRA) model the vertical propagations of SH waves through flat-layered media (1DSH) and are widely carried out to evaluate local site effects in practice. Horizontal-to-vertical spectral ratio (HVSR) technique is a cost-effective approach to extract certain site-specific information, e.g., site fundamental frequency (f(0)), but HVSR values cannot be directly used to approximate the levels of S-wave amplifications. Motivated by the work of Kawase et al. (2019), we propose a procedure to correct earthquake HVSR amplitudes for direct amplification estimations. The empirical correction compensates HVSR by generic vertical amplification spectra categorized by the vertical fundamental frequency (f(0v)) via kappa-means clustering. In this investigation, we evaluate the effectiveness of the corrected HVSR in approximating observed linear amplifications in comparison with 1DSH modellings. We select a total of 90 KiK-net (Kiban Kyoshin network) surface-downhole sites which are found to have no velocity contrasts below their boreholes and thus of which surface-to-borehole spectral ratios (SBSRs) can be taken as their empirical transfer functions (ETFs). 1DSH-based theoretical transfer functions (TTFs) are computed in the linear domain considering uncertainties in Vs profiles through randomizations. Five goodness-of-fit metrics are adopted to gauge the closeness between observed (ETF) and predicted (i.e., TTF and corrected HVSR) amplifications in both amplitude and spectral shape over frequencies from f(0) to 25 Hz. We find that the empirical correction to HVSR is highly effective and achieves a "good match" in both spectral shape and amplitude at the majority of the 90 KiK-net sites, as opposed to less than one-third for the 1DSH modelling. In addition, the empirical correction does not require a velocity model, which GRAs require, and thus has great potentials in seismic hazard assessments.
KW  - site amplification
KW  - HVSR
KW  - ground response analysis
KW  - KiK-net
KW  - earthquake
Y1  - 2020
U6  - https://doi.org/10.1016/j.soildyn.2020.106301
SN  - 0267-7261
SN  - 1879-341X
VL  - 139
PB  - Elsevier
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Zhu, Chuanbin
A1  - Cotton, Fabrice Pierre
A1  - Pilz, Marco
T1  - Detecting site resonant frequency using HVSR
BT  - Fourier versus response spectrum and the first versus the highest peak frequency
JF  - Bulletin of the Seismological Society of America : BSSA
N2  - In this investigation, we examine the uncertainties using the horizontal-to-vertical spectral ratio (HVSR) technique on earthquake recordings to detect site resonant frequencies at 207 KiK-net sites. Our results show that the scenario dependence of response (pseudospectral acceleration) spectral ratio could bias the estimates of resonant frequencies for sites having multiple significant peaks with comparable amplitudes. Thus, the Fourier amplitude spectrum (FAS) should be preferred in computing HVSR. For more than 80% of the investigated sites, the first peak (in the frequency domain) on the average HVSR curve over multiple sites coincides with the highest peak. However, for sites with multiple peaks, the highest peak frequency (f(p)) is less susceptible to the selection criteria of significant peaks and the extent of smoothing to spectrum than the first peak frequency (f(0)). Meanwhile, in comparison to the surface-to-borehole spectral ratio, f(0) tends to underestimate the predominant frequency (at which the largest amplification occurs) more than f(p). In addition, in terms of characterizing linear site response, f(p) shows a better overall performance than f(0). Based on these findings, we thus recommend that seismic network operators provide f(p) on the average HVSRFAS curve as a priority, ideally together with the average HVSRFAS curve in site characterization.
Y1  - 2020
U6  - https://doi.org/10.1785/0120190186
SN  - 0037-1106
SN  - 1943-3573
VL  - 110
IS  - 2
SP  - 427
EP  - 440
PB  - Seismological Society of America
CY  - El Cerito, Calif.
ER  - 
TY  - JOUR
A1  - Zhu, Chuanbin
A1  - Cotton, Fabrice Pierre
A1  - Pilz, Marco
T1  - Testing the Depths to 1.0 and 2.5 km/s Velocity Isosurfaces in a Velocity Model for Japan and Implications for Ground-Motion Modeling
JF  - Bulletin of the Seismological Society of America
N2  - In the Next Generation Attenuation West2 (NGA-West2) project, a 3D subsurface structure model (Japan Seismic Hazard Information Station [J-SHIS]) was queried to establish depths to 1.0 and 2.5 km/s velocity isosurfaces for sites without depth measurement in Japan. In this article, we evaluate the depth parameters in the J-SHIS velocity model by comparing them with their corresponding site-specific depth measurements derived from selected KiK-net velocity profiles. The comparison indicates that the J-SHIS model underestimates site depths at shallow sites and overestimates depths at deep sites. Similar issues were also identified in the southern California basin model. Our results also show that these underestimations and over-estimations have a potentially significant impact on ground-motion prediction using NGA-West2 ground-motion models (GMMs). Site resonant period may be considered as an alternative to depth parameter in the site term of a GMM.
Y1  - 2019
U6  - https://doi.org/10.1785/0120190016
SN  - 0037-1106
SN  - 1943-3573
VL  - 109
IS  - 6
SP  - 2710
EP  - 2721
PB  - Seismological Society of America
CY  - Albany
ER  - 
TY  - JOUR
A1  - Zhu, Chuanbin
A1  - Pilz, Marco
A1  - Cotton, Fabrice Pierre
T1  - Which is a better proxy, site period or depth to bedrock, in modelling linear site response in addition to the average shear-wave velocity?
JF  - Bulletin of earthquake engineering : official publication of the European Association for Earthquake Engineering
N2  - This study aims to identify the best-performing site characterization proxy alternative and complementary to the conventional 30 m average shear-wave velocity V-S30, as well as the optimal combination of proxies in characterizing linear site response. Investigated proxies include T-0 (site fundamental period obtained from earthquake horizontal-to-vertical spectral ratios), V-Sz (measured average shear-wave velocities to depth z, z = 5, 10, 20 and 30 m), Z(0.8) and Z(1.0) (measured site depths to layers having shear-wave velocity 0.8 and 1.0 km/s, respectively), as well as Z(x-infer) (inferred site depths from a regional velocity model, x = 0.8 and 1.0, 1.5 and 2.5 km/s). To evaluate the performance of a site proxy or a combination, a total of 1840 surface-borehole recordings is selected from KiK-net database. Site amplifications are derived using surface-to-borehole response-, Fourier- and cross-spectral ratio techniques and then are compared across approaches. Next, the efficacies of 7 single-proxies and 11 proxy-pairs are quantified based on the site-to-site standard deviation of amplification residuals of observation about prediction using the proxy or the pair. Our results show that T-0 is the best-performing single-proxy among T-0, Z(0.8), Z(1.0) and V-Sz. Meanwhile, T-0 is also the best-performing proxy among T-0, Z(0.8), Z(1.0) and Z(x-infer) complementary to V-S30 in accounting for the residual amplification after V-S30-correction. Besides, T-0 alone can capture most of the site effects and should be utilized as the primary site indicator. Though (T-0, V-S30) is the best-performing proxy pair among (V-S30, T-0), (V-S30, Z(0.8)), (V-S30, Z(1.0)), (V-S30, Z(x-infer)) and (T-0, V-Sz), it is only slightly better than (T-0, V-S20). Considering both efficacy and engineering utility, the combination of T-0 (primary) and V-S20 (secondary) is recommended. Further study is needed to test the performances of various proxies on sites in deep sedimentary basins.
KW  - Site effects
KW  - Amplification
KW  - Site proxy
KW  - Surface-to-borehole spectral ratios
KW  - KiK-net
KW  - Earthquake
Y1  - 2019
U6  - https://doi.org/10.1007/s10518-019-00738-6
SN  - 1570-761X
SN  - 1573-1456
VL  - 18
IS  - 3
SP  - 797
EP  - 820
PB  - Springer
CY  - Dordrecht
ER  - 
TY  - JOUR
A1  - Pilz, Marco
A1  - Cotton, Fabrice Pierre
A1  - Zhu, Chuanbin
T1  - How much are sites affected by 2-D and 3-D site effects?
BT  - a study based on single-station earthquake records and implications for ground motion modelling
JF  - Geophysical journal international
N2  - 1-D site response analysis dominates earthquake engineering practice, while local 2-D/3-D models are often required at sites where the site response is complex. For such sites, the 1-D representation of the soil column can account neither for topographic effects or dipping layers nor for locally generated horizontally propagating surface waves. It then remains a crucial task to identify whether the site response can be modelled sufficiently precisely by 1-D analysis. In this study we develop a method to classify sites according to their 1-D or 2-D/3-D nature. This classification scheme is based on the analysis of surface earthquake recordings and the evaluation of the variability and similarity of the horizontal Fourier spectra. The taxonomy is focused on capturing significant directional dependencies and interevent variabilities indicating a more probable 2-D/3-D structure around the site causing the ground motion to be more variable. While no significant correlation of the 1-D/3-D site index with environmental parameters and site proxies seems to exist, a reduction in the within-site (single-station) variability is found. The reduction is largest (up to 20 per cent) for purely 1-D sites. Although the taxonomy system is developed using surface stations of the KiK-net network in Japan as considerable additional information is available, it can also be applied to any (non-downhole array) site.
KW  - Earthquake ground motions
KW  - Earthquake hazards
KW  - Site effects
KW  - Wave propagation
Y1  - 2021
U6  - https://doi.org/10.1093/gji/ggab454
SN  - 0956-540X
SN  - 1365-246X
VL  - 228
IS  - 3
SP  - 1992
EP  - 2004
PB  - Oxford University Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Zhu, Chuanbin
A1  - Cotton, Fabrice
A1  - Kawase, Hiroshi
A1  - Händel, Annabel
A1  - Pilz, Marco
A1  - Nakano, Kenichi
T1  - How well can we predict earthquake site response so far?
BT  - site-specific approaches
JF  - Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute
N2  - Earthquake site responses or site effects are the modifications of surface geology to seismic waves. How well can we predict the site effects (average over many earthquakes) at individual sites so far? To address this question, we tested and compared the effectiveness of different estimation techniques in predicting the outcrop Fourier site responses separated using the general inversion technique (GIT) from recordings. Techniques being evaluated are (a) the empirical correction to the horizontal-to-vertical spectral ratio of earthquakes (c-HVSR), (b) one-dimensional ground response analysis (GRA), and (c) the square-root-impedance (SRI) method (also called the quarter-wavelength approach). Our results show that c-HVSR can capture significantly more site-specific features in site responses than both GRA and SRI in the aggregate, especially at relatively high frequencies. c-HVSR achieves a "good match" in spectral shape at similar to 80%-90% of 145 testing sites, whereas GRA and SRI fail at most sites. GRA and SRI results have a high level of parametric and/or modeling errors which can be constrained, to some extent, by collecting on-site recordings.
KW  - Site response
KW  - site effects
KW  - HVSR
KW  - ground response analysis
KW  - square-root-impedance
KW  - earthquake
Y1  - 2022
U6  - https://doi.org/10.1177/87552930211060859
SN  - 8755-2930
SN  - 1944-8201
VL  - 38
IS  - 2
SP  - 1047
EP  - 1075
PB  - Sage Publ.
CY  - Thousand Oaks
ER  -