This study is focused on intraslab earthquakes occurring within subducting oceanic plate. Recently intraslab earthquakes are becoming increasingly important as targets of strong motion prediction, partly because a large intraslab earthquake is anticipated to occur within the subducting Philippine Sea Plate, just beneath metropolitan Tokyo.
Currently, strong motion prediction is largely dependent on so called the “characterized source model”, which is a combination of rectangular asperities, however, the authors have been proposing a much simpler source model called the “pseudo point source model”. The model considers one or more subevents generating strong ground motions. In the model, the spatio-temporal distribution of slip within a subevent is not modeled. Instead, the source spectrum associated with the rupture of a subevent is modeled and it is assumed to follow the omega-square model. The model involves much less model parameters than conventional models; thus it could be suitable for practical purposes.
The pseudo point-source model had been validated for several earthquakes including the 2011 Tohoku earthquake, however, its applicability to intraslab earthquakes has not been sufficiently investigated. Therefore, in this study, the pseudo point source model was applied to six large intraslab earthquakes in and around Japan which provided strong motion records.
The results revealed that, if the source parameters were appropriately selected, strong motion records due to intraslab earthquakes can well be explained with the pseudo point-source model. A wide range of records, some including direct effects of rupture process and some including dominant effects of ground response, can be explained within the framework of the pseudo point-source model. Empirical relations between source parameters and seismic moment were derived, which were found to be consistent with existing relations for intraslab earthquakes based on the characterized source model.

Key Words: intraslab earthquake, pseudo point-source model, strong motion simulation, ω-2 model