Can site effects be estimated with respect to a distant reference station? Performance of the spectral factorization of coda waves

Grendas, I.; Theodoulidis, Nikos; Bard, P.-Y.; Perron, Vincent; Hatzidimitriou, P. M.; Hollender, Fabrice

doi:10.1093/gji/ggac040

Cited by 3 publications

(1 citation statement)

References 39 publications

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“…This step, however, requires defining not only the modulus of the non-linear transfer function, but also its phase. In that aim, we proceed in the same way as proposed in Brax et al, (2018); Sèbe et al, (2018) and Grendas et al, (2022).…”

Section: Figurementioning

confidence: 99%

Empirical approches for non-linear site response: results from the ESG6-blind test.

Régnier

Bard

Cruz

et al. 2023

Preprint

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As a contribution to step 3 of the ESG6 blind prediction exercise, we present an application of two different, purely empirical approaches to estimate the strong ground motion at a soft site ("KUMA") from the observed ground motion at a reference rock site ("SEVO") for the two largest shocks of the Kumamoto 2016 sequence (a foreshock with Mj=6.5, and the mainshock with Mj=7.3). The two methods estimate the non-linear transfer function between a reference rock and a sedimentary site by modifying the linear transfer function derived from weak motion recordings. The modification is based either on a machine learning tool based on a wide collection of Japanese weak and strong motion recordings and the associated site metadata (method M1), or on an estimate of a site-specific parameter related to an average non-linear site response (M2). The acceleration time series are then derived at the sedimentary site of interest using an estimation of the time delay between wave arrivals at the rock and site stations, and a minimum phase assumption for the site transfer function. These predictions were made blindly, but after the ESG6 conference they could be compared both with the actual ground motion recorded at KUMA during the two shocks, and the average and range of all other predictions preformed for this benchmark. The quality of predictions is quantified through various "goodness of fit" (GOF) measures. The agreement may be considered as "excellent" for the foreshock and "good" for the mainshock for usual engineering ground motion parameters (peak values, response spectra, integral parameters), but is very poor in terms of waveform details – as usual for all ground motion predictions even in the linear domain –. The performance of these two purely empirical approaches is at least comparable to those of the numerical simulation methods for the foreshock – if not better -, and slightly worse for the (largest) mainshock. This may come either from an underestimation of non-linear effects, or from the relatively large distance (8 km) between the reference and the target site which limits the reliability of the empirical transfer functions and thus the applicability of the approaches used here for such an instrumental layout. Both of these purely empirical methods provide an honorable prediction of the Fourier spectra and acceleration time histories of the two target events, as the methods required only recordings of weak motions at the target and a referent sites and very simple description of the soil profile. The use of moderate motions to constrain the frequency shift prediction for the second method and the consideration of an alternative phase modification are possible ways to improvement.

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Section: Figurementioning

confidence: 99%

Empirical approches for non-linear site response: results from the ESG6-blind test.

Régnier

Bard

Cruz

et al. 2023

Preprint

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Empirical approaches for non-linear site response: results for the ESG6-blind test

Régnier,

Bard,

Castro-Cruz

et al. 2024

Earth Planets Space

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As a contribution to step 3 of the ESG6 blind prediction exercise, we present an application of two different, purely empirical approaches to estimate the strong ground motion at a soft site ("KUMA") from the observed ground motion at a reference rock site ("SEVO") for the two largest shocks of the Kumamoto 2016 sequence. The two methods estimate the non-linear transfer function between a reference rock and a sedimentary site by modifying the linear transfer function derived from weak motion recordings. The modification is based either on a machine learning tool based on a wide collection of Japanese weak and strong motion recordings and the associated site metadata (method 1), or on an estimate of a site-specific parameter related to an average non-linear site response (method 2). The acceleration time series are then derived at the sedimentary site of interest using an estimation of the time delay between wave arrivals at the rock and site stations, and a minimum phase assumption for the site transfer function. These predictions were made blindly, but after the ESG6 conference they could be compared both with the actual ground motion recorded at KUMA during the two shocks, and the average and range of all other predictions preformed for this benchmark. Both of these purely empirical methods provide an honorable prediction of usual engineering ground motion parameters of the two target events. The performance of these two purely empirical approaches is at least comparable to those of the numerical simulation methods for the foreshock—if not better—and slightly worse for the (largest) mainshock. As the methods required only recordings of weak motions at the target and a referent sites and very simple description of the soil profile. The use of moderate motions to constrain the frequency shift prediction for the second method and the consideration of an alternative phase modification are possible ways to improvement. Graphical Abstract

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Shallow Structure and Seismic Amplification Effects in the Weifang Segment of the Tanlu Fault Zone Based on the Spectral Ratio Method

Zhou,

Yao

2024

Seismological Research Letters

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The Weifang segment of the Tanlu fault zone (TLFZ) is located in the central section of the TLFZ, eastern China, and has been identified as an earthquake gap zone. Previous studies in the region have mainly focused on the crustal velocity structure and anisotropy, with limited attention to the shallow near-surface structures. In this study, we analyzed the distribution of sediment thickness and evaluated the seismic amplification effects in the Weifang segment of the TLFZ using the horizontal-to-vertical spectral ratio (HVSR) method and the standard spectral ratio (SSR) method. The data we used are from a dense array of 302 three-component seismometers deployed in 2017 for three months. The lowest peak frequency of HVSR indicates that the northwestern part of the study area exhibits relatively thicker sedimentary deposits, estimated to be 800–1200 m in thickness, consistent with both tomographic and geological studies. The SSRs are calculated from 43 regional and teleseismic earthquakes with respect to 12 reference stations. The results from SSR show strong amplification in the 0.2–2 Hz frequency range for sites on the northwestern part, and the amplitude can be up to 15 times larger than that of the bedrock site. We also find significant amplification effects as well as thick sedimentary layers at specific stations along the eastern branch of the TLFZ, suggesting a localized low-velocity zone along the fault. Our results also demonstrate that using the single-site seismic method can provide new constraints on the fine structure and site responses of the fault zone, which are important for seismic hazard assessment.

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Can site effects be estimated with respect to a distant reference station? Performance of the spectral factorization of coda waves

Cited by 3 publications

References 39 publications

Empirical approches for non-linear site response: results from the ESG6-blind test.

Empirical approches for non-linear site response: results from the ESG6-blind test.

Empirical approaches for non-linear site response: results for the ESG6-blind test

Shallow Structure and Seismic Amplification Effects in the Weifang Segment of the Tanlu Fault Zone Based on the Spectral Ratio Method

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