Ground-Motion Prediction Equations for Subduction Interface Earthquakes in Japan Using Site Class and Simple Geometric Attenuation Functions

We presented a set of ground-motion prediction equations (GMPEs) for the horizontal components of strong-motion records from subduction interface events in Japan. We assembled and processed in a consistent manner a large set of strong-motion records from reliably identified subduction interface events up to the end of 2012. The GMPEs were based on a set of simple geometric attenuation functions, and site class was based on site period as the site parameter. We adopted a bilinear magnitude-scaling function hinged at M-w 7.1 and found that the magnitude-scaling rate for large events is much smaller than that for smaller events. To reliably determine the magnitude-scaling rate for events with M-w >= 7.1, we used a set of strong-motion records obtained since 1968 to increase the number of records from large events. A small number of strong-motion records are from recording stations with inferred site classes using the response spectral ratio of the horizontal-to-vertical components or a geological description of the surface soil layers. The effect of site information quality for subduction interface events was examined using a goodness-of-fit parameter from a dataset with or without the sites having an inferred site class. The site information quality made a significant difference at all spectral periods, because the model fit improved significantly when the sites with inferred classes were excluded. We modeled the effect of volcanic zones using an an-elastic attenuation coefficient applied to the horizontal portion of the seismic-wave travel distance within a set of assumed volcanic zones. The within-event residuals were approximately separated into within-site and between-site components, and the corresponding standard deviations were calculated using a random effects model. The between-site standard deviations vary significantly among site classes and with spectral periods.