Ground Motion Prediction Equations for the Vertical Ground Motion Component Based on the NGA-W2 Database

Empirical ground motion models for the vertical component from shallow crustal earthquakes in active tectonic regions are derived using the PEER NGA-West2 database. The model is applicable to magnitudes 3.0–8.0, distances of 0–300 km, and spectral periods of 0–10 s. The model input parameters are the same as used by Abrahamson et al. (2014) except that the nonlinear site response and depth to bedrock effects are evaluated but found to be insignificant. Regional differences in large distance attenuation and site amplification scaling between California, Japan, China, Taiwan, Italy, and the Middle East are included. Scaling for the hanging-wall effect is incorporated using the constraints from numerical simulations by Donahue and Abrahamson (2014). The standard deviation is magnitude dependent with smaller magnitudes leading to larger standard deviations at short periods but smaller standard deviations at long periods. The vertical ground motion model developed in this study can be paired with the horizontal component model proposed by Abrahamson et al. (2014) to produce a V/H ratio. For applications where the horizontal spectrum is derived from the weighted average of several horizontal ground motion models, a V/H model derived directly from the V/H data (such as Gülerce and Abrahamson 2011) should be preferred.