Application of Horizontal-to-Vertical Spectral Ratios of Earthquake Ground Motions to Identify Subsurface Structures at and around the K-NET Site in Tohoku, Japan

Nagashima, Fumiaki; Matsushima, Shinichi; Kawase, Hiroshi; Sánchez‐Sesma, Francisco J.; Hayakawa, T.; Satoh, Toshimi; Oshima, Mitsutaka

doi:10.1785/0120130219

Cited by 73 publications

(64 citation statements)

References 15 publications

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“…Since we are applying the same inversion procedure developed for the EHVR by Nagashima et al (2014Nagashima et al ( , 2017, we only briefly describe the basic explanation of the assumptions and the method used.…”

Section: Velocity Inversion Using the Theory For Ehvrmentioning

confidence: 99%

“…The inversion scheme used here is basically the same as those proposed by Nagashima et al (2014Nagashima et al ( , 2017, who extensively studied the velocity structures at the MYG004K-NET site and its neighboring areas using a temporary deployment of aftershock observation for the 2011 Tohoku earthquake. For the inversion of S-wave velocity structures, they used the scheme proposed by Yamanaka (2007), the so-called hybrid heuristic search (HHS) method.…”

Section: Ehvr Inversionmentioning

confidence: 99%

“…7. We use the best-fit model with 14 layers as a reference for MYG004 (Nagashima et al 2014(Nagashima et al , 2017 and omit two layers in each step from the bottom of the reference model. As the bottommost P-and S-wave velocities decrease, the peak in the lower frequency range disappears, as expected.…”

Section: Ehvr Inversionmentioning

confidence: 99%

“…Fig. 7 A parametric study of the effect of the bottommost layer on the theoretical EHVR for the best-fit model at MYG006 with 14 layers (Nagashima et al 2014(Nagashima et al , 2017. When we omit the two layers in one step from the original velocity model shown in the right, not only the amplitude of the lowest frequency peak but also the amplitudes of peaks and troughs in the higher frequency range are strongly affected is larger than MHVR for frequencies larger than 1 Hz, which is a direct consequence of the spectral difference shown in the previous section.…”

Section: Empirical Emrmentioning

confidence: 99%

“…Then, Kawase et al (2011) extended the idea of DFC to the stack of horizontal-to-vertical ratios of earthquakes (EHVR) and provided a simple theoretical formula assuming equipartition of energy in the incident waves at the bedrock (i.e., equipartition inside the half-space). It turned out that this is a powerful tool to determine the S-wave velocity structure below the observed site of earthquakes down to the seismological bedrock, as evidenced by Ducellier et al (2013), Nagashima et al (2014Nagashima et al ( , 2017 and Fukihara et al (2015).…”

Section: Introductionmentioning

confidence: 99%

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Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

Kawase

Mori

Nagashima

2018

Earth Planets Space

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We have been discussing the validity of using the horizontal-to-vertical spectral ratios (HVRs) as a substitute for S-wave amplifications after Nakamura first proposed the idea in 1989. So far a formula for HVRs had not been derived that fully utilized their physical characteristics until a recent proposal based on the diffuse field concept. There is another source of confusion that comes from the mixed use of HVRs from earthquake and microtremors, although their wave fields are hardly the same. In this study, we compared HVRs from observed microtremors (MHVR) and those from observed earthquake motions (EHVR) at one hundred K-NET and KiK-net stations. We found that MHVR and EHVR share similarities, especially until their first peak frequency, but have significant differences in the higher frequency range. This is because microtremors mainly consist of surface waves so that peaks associated with higher modes would not be prominent, while seismic motions mainly consist of upwardly propagating plain body waves so that higher mode resonances can be seen in high frequency. We defined here the spectral amplitude ratio between them as EMR and calculated their average. We categorize all the sites into five bins by their fundamental peak frequencies in MHVR. Once we obtained EMRs for five categories, we back-calculated EHVRs from MHVRs, which we call pseudo-EHVRs (pEHVR). We found that pEHVR is much closer to EHVR than MHVR. Then we use our inversion code to invert the one-dimensional S-wave velocity structures from EHVRs based on the diffuse field concept. We also applied the same code to pEHVRs and MHVRs for comparison. We found that pEHVRs yield velocity structures much closer to those by EHVRs than those by MHVRs. This is natural since what we have done up to here is circular except for the average operation in EMRs. Finally, we showed independent examples of data not used in the EMR calculation, where better ground structures were successfully identified from pEHVRs again. Thus we proposed here a simple empirical method to estimate S-wave velocity structures using single-station microtremor records, which is the most cost-effective method to characterize the site effects.Keywords: Site effect, Subsurface structure, Seismological bedrock, Horizontal-to-vertical ratio, Hybrid heuristic search, S-wave, P-wave © The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

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Section: Velocity Inversion Using the Theory For Ehvrmentioning

confidence: 99%

Section: Ehvr Inversionmentioning

confidence: 99%

Section: Ehvr Inversionmentioning

confidence: 99%

Section: Empirical Emrmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

Kawase

Mori

Nagashima

2018

Earth Planets Space

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A new empirical method for obtaining horizontal site amplification factors with soil nonlinearity

Wang

Nagashima

Kawase

2021

Earthq Engng Struct Dyn

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Currently, the theoretical prediction of soil amplification considering nonlinear soil behaviors can be implemented through nonlinear analysis of soil layers in time domains. However, in such theoretical methods, we need detailed velocity information down to the seismological bedrock and nonlinear properties of sediments, which are challenging to obtain in a wider area for a scenario-type seismic risk evaluation. Recently, using diffuse-field theory, we found that the horizontal-to-vertical spectral ratio of Earthquake (EHVR) is the ratio of the S-wave horizontal transfer function with respect to the P-wave vertical transfer function with the vertical incidence from the seismological bedrock with a coefficient for HVRs at the bedrock. Therefore, if there is no significant nonlinearity in the P-wave vertical transfer function during strong shaking, we can regard soil nonlinearity emerging on the EHVR as the nonlinearity of the S-wave horizontal amplification. In this study, we tried to distinguish the difference between the EHVRs in the linear and nonlinear cases, quantify the difference, and utilize a creative empirical approach to acquire the S-wave horizontal amplification factors with soil nonlinearity to improve the quality of strong motion prediction in the near field in the future.

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A hybrid approach for deriving horizontal site amplification factors considering both the similarity of HVSR_E and the vertical amplification correction function

Wang

Nakano²,

Ito

et al. 2022

Earthq Engng Struct Dyn

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Under hypothetical and idealized conditions, the horizontal site amplification factor (HSAF) is defined as the ratio of the horizontal Fourier amplitude spectrum (FAS) at a point on the Earth's surface with respect to the horizontal FAS at the identical location but on the outcropping seismological bedrock. The HSAF reflects the profile of local sedimentary soils and weathered rock formations, indicating site effects. In most cases, such an idealized HSAF is difficult to measure directly. Thus, quantitatively estimating a HSAF value is a crucial task in strong-motion prediction over the last century. Fortunately, many strong-motion stations have been constructed throughout Japan, facilitating the characterization of HSAFs down to seismological bedrock at more than 1600 observational sites by the generalized inversion technique (GIT). First, this study reported the similarity distribution of the HSAF and the horizontal-to-vertical spectral ratio of earthquakes (HVSR E ). Subsequently, we proposed a hybrid method from a novel aspect for estimating HSAF in terms of the observed similarity distribution and the vertical amplification correction function (VACF) proposed previously. Compared with the direct use of HVSR E for substituting HSAF, the hybrid method proposed herein demonstrated an improvement of greater than 30% in terms of the residuals between estimated HSAFs and those separated from observations.

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Application of Horizontal-to-Vertical Spectral Ratios of Earthquake Ground Motions to Identify Subsurface Structures at and around the K-NET Site in Tohoku, Japan

Cited by 73 publications

References 15 publications

Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

A new empirical method for obtaining horizontal site amplification factors with soil nonlinearity

A hybrid approach for deriving horizontal site amplification factors considering both the similarity of HVSR_E and the vertical amplification correction function

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Application of Horizontal-to-Vertical Spectral Ratios of Earthquake Ground Motions to Identify Subsurface Structures at and around the K-NET Site in Tohoku, Japan

Cited by 73 publications

References 15 publications

Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

Difference of horizontal-to-vertical spectral ratios of observed earthquakes and microtremors and its application to S-wave velocity inversion based on the diffuse field concept

A new empirical method for obtaining horizontal site amplification factors with soil nonlinearity

A hybrid approach for deriving horizontal site amplification factors considering both the similarity of HVSRE and the vertical amplification correction function

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A hybrid approach for deriving horizontal site amplification factors considering both the similarity of HVSR_E and the vertical amplification correction function