Comment on "Ground Motion Attenuation Relations for Subduction Zones"

The amount of strong ground motion data available is increasing as more observation systems come on line. Many attenuation relationships have been developed by regression analysis on such data. The selection of data prior to analysis is, however, an important task that is fundamental to the process. For example, irregularly large amplitudes from events in a subduction zone may be observed at great hypocentral distances up to several hundred kilometers. Youngs et al. (1997) developed ground motion attenuation relations for subduction zones using observations including those at large hypocentral distances. However, these data sometimes lead to unreasonable attenuation rates, as I show here. Near Japan, greater intensities have often been observed along the Pacific coast than along the Japan Sea coast when the source was deep in the Japan Sea region (Table 1). As shown in Figure1, the seismic rays of such events pass along the Pacific plate and then...