A Method for Including Path Effects in Ground-Motion Prediction Equations: An Example Using the Mw 9.0 Tohoku Earthquake Aftershocks

Past studies in tectonic regions dominated by subduction zones that result in the creation of volcanic belts, such as New Zealand and Japan, have pointed to higher attenuation rates across the volcanic regions. This study uses the downhole motions recorded at KiK-net stations from 117 aftershocks that hit Japan after the great M-w 9.0 Tohoku earthquake to quantify region-dependent strong-motion attenuation rates. To this end, an approach to include path effects in the development of ground-motion prediction equations (GMPEs) is presented. In this approach, regional path terms are constrained using the strong-motion data. The constraint on path terms also makes this methodology suitable for the development of GMPEs that permit the removal of the ergodic assumption on path. The analysis results indicate the viability of the proposed methodology for constraining regional path terms and provide an estimate of single-station, single-path standard deviations. In addition, results confirm that the attenuation rate in volcanic regions is significantly higher than in nonvolcanic regions. Finally, a moderate correlation coefficient was found between the attenuation rate for weak and strong ground motions.