Predicted results of weak and strong ground motions at the target site of the blind prediction exercise as steps-2 and -3, Report for the experiments for the 6th international symposium on effects of surface geology on seismic motion

Abstract

In this study, we compared observations and predictions submitted by participants for blind prediction experiments for ground motions using aftershocks, foreshock, and mainshock of the 2016 Kumamoto earthquake sequence, Japan, to improve our understanding of the quality of state-of-the-art methods on the reproducibility of the effects of surface geology on seismic motions. In the blind predictions, 1D, 2D, and 3D methods, Green’s function methods, spectral ratio approaches, and other approaches were applied. As for PGA/PGV, acceleration/velocity duration, Fourier spectrum, pseudo-velocity response spectrum, and site amplification factors, the observed values are mostly within the range of average ± σ of all the predictions in the case of weak and strong ground motions. The results of the mean absolute percentage errors for these indices show that the applied methods can predict weak and strong ground motions for the three components in the range of one-half to twice the observations. The average goodness-of-fit (GOF) scores for weak and strong ground motions indicate either a very good fit (6.5–8) or a good fit (4.5–6.5) for the three components. Finally, examples of the categorized methods are quite limited; however, results indicate that the predictions by all the categorized methods can adequately reproduce weak and strong ground motions within either a very good or good fit. Although we could not find a significant difference in the results from the categorized methods, scores by the 2D and 3D methods in the frequency range of 0.5–1 and 1–2 Hz for all the blind predictions are higher than the scores by the other methods. The GOF score for the part after the S-wave by the 2D and 3D methods is higher than that by the 1D method. This supports that the predictions by the 2D and 3D methods due to the accounting of the proper geometry could reproduce the basin-induced and/or basin-transduced surface waves excited by the basin-edge effect more than the 1D method using the earthquake record observed at the reference site.Graphical