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 Mw 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 Mw≥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 anelastic 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.
Online Material: Figures showing distributions of between‐event and within‐event residuals.