Damping Modification Factors for Horizontal and Vertical Acceleration Spectra from Offshore Ground Motions in the Japan Sagami Bay Region

Abstract

Damping modification factors (DMFs) are used to scale the 5%-damped response spectra for the seismic design of structures with different damping ratios. However, there is no DMF model for offshore engineering response spectra at present. Using 892 offshore and 4033 onshore ground-motion records from the Kyoshin net, the difference between offshore and onshore DMFs are revealed by DMF ratios and t tests and whether site conditions need to be incorporated in offshore DMF models are determined. The between-event residual distribution shows that DMFs depend on the focal depth. The results show that the DMFs from the offshore and onshore ground motions differ significantly for most spectral periods, and the impact of the site condition on offshore DMF is very slight. The offshore DMF models for the horizontal and vertical acceleration spectra from the Japan Sagami Bay region are presented from spectra of 34 spectral periods and 10 damping ratios, in which only spectral periods and damping ratios are considered as variables. The uncertainty in the DMF model mainly depends on the path and site effects, and the standard deviations of DMFs for the vertical component are slightly less than those for the horizontal component. All standard deviations are modeled by a set of quadratic functions related to damping ratios. A comparison between the offshore DMF model in this study and those derived from onshore ground motions indicates that the differences are significant. The spectra from the Hu et al. (2020) study for offshore ground motions adjusted by the DMF models are used as our example applications.

An offshore non-ergodic ground motion model for subduction earthquakes in Japan Trench area

“…The current research indicates that the offshore ground motion is significantly different from the onshore ground motion in response spectrum (Chen et al, 2015; Dhakal et al, 2021; Hu et al, 2020; Zhang and Zheng, 2019), temporal characteristics (Zhang and Zheng, 2020), elastic relative and absolute input energy (Hu and Tan, 2022), vertical-to-horizontal spectrum ratio (Boore and Smith, 1999; Chen et al, 2017; Tan and Hu, 2021), damping modification factors (Hu et al, 2022b), and seismic ground motion simulation (Lan et al, 2021; Li et al, 2011), especially for subduction earthquakes. Furthermore, Tan and Hu (2023) compared the differences in horizontal peak ground acceleration (PGA), spectral acceleration, frequency content, and significant duration between offshore and onshore ground motion characteristics using two large offshore earthquakes (February 13, 2021, M w 7.1 and March 17, 2022, M w 7.4), wherein the offshore records were from the S-net network and the onshore records were from the K-NET network.…”

The Derivation of Vertical Damping Reduction Factors for the Design and Analysis of Structures Using Acceleration, Velocity, and Displacement Spectra

“…Based on several studies [32,33,35,36] and the observations in this study, the polynomial function of natural logarithms of the natural vibration period and damping ratio parameters can be used to describe the relations of the DRFs.…”

“…In addition, he developed simplified empirical formulations to compute the DRF for the vertical component. Hu et al [36] employed 892 offshore and 4033 onshore ground motion records from the Kyoshin network to exhibit the differences in the DRFs of offshore and onshore ground motions. They stressed that the influence of the site conditions on offshore DRFs is extremely minor.…”

Damping‐dependent correlations between horizontal‐horizontal, horizontal‐vertical, and vertical‐vertical pairs of spectral accelerations

“…Since the pioneering work of Newmark and Hall, 21 development of ground motion prediction equations (GMPEs) and damping scaling factors (DSFs) for non-5%-damped horizontal and vertical spectral ordinates has attracted increasing attention in the past few decades (e.g., refs. 1,2,19,[22][23][24][25][26][27]. The GMPEs and DSFs can be used to describe the marginal distribution of SA(T, ξ), but correlation coefficients among SAs are additionally required to establish the joint distribution of a SA-vector (e.g., refs.…”