@article{ZhuCottonKwaketal.2021, author = {Zhu, Chuanbin and Cotton, Fabrice and Kwak, Dong-Youp and Ji, Kun and Kawase, Hiroshi and Pilz, Marco}, title = {Within-site variability in earthquake site response}, series = {Geophysical journal international}, volume = {229}, journal = {Geophysical journal international}, number = {2}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0956-540X}, doi = {10.1093/gji/ggab481}, pages = {1268 -- 1281}, year = {2021}, abstract = {The within-site variability in site response is the randomness in site response at a given site from different earthquakes and is treated as aleatory variability in current seismic hazard/risk analyses. In this study, we investigate the single-station variability in linear site response at K-NET and KiK-net stations in Japan using a large number of earthquake recordings. We found that the standard deviation of the horizontal-to-vertical Fourier spectral ratio at individual sites, that is single-station horizontal-to-vertical spectral ratio (HVSR) sigma sigma(HV,s), approximates the within-site variability in site response quantified using surface-to-borehole spectral ratios (for oscillator frequencies higher than the site fundamental frequency) or empirical ground-motion models. Based on this finding, we then utilize the single-station HVSR sigma as a convenient tool to study the site-response variability at 697 KiK-net and 1169 K-NET sites. Our results show that at certain frequencies, stiff, rough and shallow sites, as well as small and local events tend to have a higher sigma(HV,s). However, when being averaged over different sites, the single-station HVSR sigma, that is sigma(HV), increases gradually with decreasing frequency. In the frequency range of 0.25-25 Hz, sigma(HV) is centred at 0.23-0.43 in ln scales (a linear scale factor of 1.26-1.54) with one standard deviation of less than 0.1. sigma(HV) is quite stable across different tectonic regions, and we present a constant, as well as earthquake magnitude- and distance-dependent sigma(HV) models.}, language = {en} } @article{PilzCottonRazafindrakotoetal.2020, author = {Pilz, Marco and Cotton, Fabrice and Razafindrakoto, Hoby Njara Tendrisoa and Weatherill, Graeme and Spies, Thomas}, title = {Regional broad-band ground-shaking modelling over extended and thick sedimentary basins}, series = {Bulletin of earthquake engineering : official publication of the European Association for Earthquake Engineering}, volume = {19}, journal = {Bulletin of earthquake engineering : official publication of the European Association for Earthquake Engineering}, number = {2}, publisher = {Springer}, address = {Dordrecht}, issn = {1570-761X}, doi = {10.1007/s10518-020-01004-w}, pages = {581 -- 603}, year = {2020}, abstract = {The simulation of broad-band (0.1 to 10 + Hz) ground-shaking over deep and spatially extended sedimentary basins at regional scales is challenging. We evaluate the ground-shaking of a potential M 6.5 earthquake in the southern Lower Rhine Embayment, one of the most important areas of earthquake recurrence north of the Alps, close to the city of Cologne in Germany. In a first step, information from geological investigations, seismic experiments and boreholes is combined for deriving a harmonized 3D velocity and attenuation model of the sedimentary layers. Three alternative approaches are then applied and compared to evaluate the impact of the sedimentary cover on ground-motion amplification. The first approach builds on existing response spectra ground-motion models whose amplification factors empirically take into account the influence of the sedimentary layers through a standard parameterization. In the second approach, site-specific 1D amplification functions are computed from the 3D basin model. Using a random vibration theory approach, we adjust the empirical response spectra predicted for soft rock conditions by local site amplification factors: amplifications and associated ground-motions are predicted both in the Fourier and in the response spectra domain. In the third approach, hybrid physics-based ground-motion simulations are used to predict time histories for soft rock conditions which are subsequently modified using the 1D site-specific amplification functions computed in method 2. For large distances and at short periods, the differences between the three approaches become less notable due to the significant attenuation of the sedimentary layers. At intermediate and long periods, generic empirical ground-motion models provide lower levels of amplification from sedimentary soils compared to methods taking into account site-specific 1D amplification functions. In the near-source region, hybrid physics-based ground-motions models illustrate the potentially large variability of ground-motion due to finite source effects.}, language = {en} } @article{WeatherillKothaCotton2020, author = {Weatherill, Graeme and Kotha, Sreeram Reddy and Cotton, Fabrice}, title = {Re-thinking site amplification in regional seismic risk assessment}, series = {Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute}, volume = {36}, journal = {Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute}, number = {1_SUPPL}, publisher = {Sage Publishing}, address = {Thousand Oaks, CA}, issn = {8755-2930}, doi = {10.1177/8755293019899956}, pages = {274 -- 297}, year = {2020}, abstract = {Probabilistic assessment of seismic hazard and risk over a geographical region presents the modeler with challenges in the characterization of the site amplification that are not present in site-specific assessment. Using site-to-site residuals from a ground motion model fit to observations from the Japanese KiK-net database, correlations between measured local amplifications and mappable proxies such as topographic slope and geology are explored. These are used subsequently to develop empirical models describing amplification as a direct function of slope, conditional upon geological period. These correlations also demonstrate the limitations of inferring 30-m shearwave velocity from slope and applying them directly into ground motion models. Instead, they illustrate the feasibility of deriving spectral acceleration amplification factors directly from sets of observed records, which are calibrated to parameters that can be mapped uniformly on a regional scale. The result is a geologically calibrated amplification model that can be incorporated into national and regional seismic hazard and risk assessment, ensuring that the corresponding total aleatory variability reflects the predictive capability of the mapped site proxy.}, language = {en} } @article{ZhuCottonKawaseetal.2022, author = {Zhu, Chuanbin and Cotton, Fabrice and Kawase, Hiroshi and H{\"a}ndel, Annabel and Pilz, Marco and Nakano, Kenichi}, title = {How well can we predict earthquake site response so far?}, series = {Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute}, volume = {38}, journal = {Earthquake spectra : the professional journal of the Earthquake Engineering Research Institute}, number = {2}, publisher = {Sage Publ.}, address = {Thousand Oaks}, issn = {8755-2930}, doi = {10.1177/87552930211060859}, pages = {1047 -- 1075}, year = {2022}, abstract = {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.}, language = {en} }