Spectral damping scaling factors for horizontal components of ground motions from subduction earthquakes using NGA-Subduction data

Abstract

This article develops global models of damping scaling factors (DSFs) for subduction zone earthquakes that are functions of the damping ratio, spectral period, earthquake magnitude, and distance. The Next Generation Attenuation for subduction earthquakes (NGA-Sub) project has developed the largest uniformly processed database of recorded ground motions to date from seven subduction regions: Alaska, Cascadia, Central America and Mexico, South America, Japan, Taiwan, and New Zealand. NGA-Sub used this database to develop new ground motion models (GMMs) at a reference 5% damping ratio. We worked with the NGA-Sub project team to develop an extended database that includes pseudo-spectral accelerations (PSA) for 11 damping ratios between 0.5% and 30%. We use this database to develop parametric models of DSF for both interface and intraslab subduction earthquakes that can be used to adjust any subduction GMM from a reference 5% damping ratio to other damping ratios. The DSF is strongly influenced by the response spectral shape and the duration of motion; therefore, in addition to the damping ratio, the median DSF model uses spectral period, magnitude, and distance as surrogate predictor variables to capture the effects of the spectral shape and the duration of motion. We also develop parametric models for the standard deviation of DSF. The models presented in this article are for the RotD50 horizontal component of PSA and are compared with the models for shallow crustal earthquakes in active tectonic regions. Some noticeable differences arise from the considerably longer duration of interface records for very large magnitude events and the enriched high-frequency content of intraslab records, compared with shallow crustal earthquakes. Regional differences are discussed by comparing the proposed global models with the data from each subduction region along with recommendations on the applicability of the models.

NGA-Subduction research program

“…For NGA-West2, Rezaeian et al (2014b) developed a parametric DSF model for damping ratios of 0.5%–30%. As part of NGA-Sub, magnitude- and distance-dependent parametric models of the DSF for subduction interface and intraslab earthquakes for the horizontal (RotD50) component of ground motion were developed by Rezaeian et al (2021a). The functional form for the DSF model is the same as that of the NGA-West2 DSF model, but the coefficients were computed using the NGA-Sub database.…”

“…The new subduction DSF model is applicable to periods longer than 0.1 s. Figure 7 presents the PSA for various damping ratios generated for M 9 interface and M 7 slab events at a distance of R RUP = 75 km. In this figure, the 5%-damped PSA is the average of KBCG and PSBAH assuming Z TOR = 10 km and Z HYP (hypocentral depth) = 20 km for the interface scenario, and Z TOR = 50 km and Z HYP = 50 km for the slab scenario (Rezaeian et al, 2021a). Both scenarios are for V S 30 = 760 m/s and default basin effects.…”

“…Both scenarios are for V S 30 = 760 m/s and default basin effects. A parametric model for the standard deviation of the DSF was also developed empirically by Rezaeian et al (2021a) for subduction earthquakes that can be used to adjust the aleatory variability of the 5%-damped PSA.…”

“…Damped PSA generated by applying the DSFs for interface (a) and slab (b) scenarios (adapted from Rezaeian et al, 2021a). The base 5%-damped spectra are based on the average of KBCG and PSBAH for V S 30 = 760 m/s.…”

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

“…As one of the most representative intensity measures (IMs), the 5%‐damped (pseudo) spectral acceleration at an oscillator period ( T ), denoted as SA ( T , 5%), has been widely used to represent the characteristics of earthquake ground motions. Yet, the spectral accelerations with other damping ratio ( ξ ) values can be of interest for different types of structures 1–3 . As are related to the energy dissipation, the damping ratios can be larger than 5% for structures with base‐isolation systems and energy‐dissipation devices (e.g., ref.…”