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We proposed a new procedure for evaluating the parameters of the asperity models for predicting strong ground motions from inland earthquakes caused by long strike-slip faults. The evaluation formula of averaged dynamic stress drops obtained by Irie et al. (2010)1) for surface ruptured faults 15 to 100 km long was adopted in our procedure, because the evaluation formula of the averaged static stress drops for circular cracks, commonly adopted in existing procedures, could not be applied to surface ruptured faults or long faults. The dynamic stress drop averaged on the entire fault was estimated to be 34 bars from the data of the rupture areas and the seismic moments of actual earthquakes, and the dynamic stress drop on the asperity was estimated to be 122 bars from the data of the short-period levels and the seismic moments of actual earthquakes. These results led to the conclusions that the asperity areas were 23 % of the entire ruptured areas.

Short active faults observed on the ground surface have been supposed to indicate longer subsurface faults in the seismogenic layer. However, no concrete procedures have been proposed so far for modeling the subsurface faults for predicting strong ground motions. Hence, we surveyed several important research papers, and proposed a procedure for modeling the subsurface faults. Here, the seismic moment M0 of 7.5×1025 dyne•cm was assumed as the minimum size of the source for the case that any short active faults were observed on the surface. The modeling procedure was based on the asperity model, that was adopted by the Headquaters of Earthquake Research Promotion (2005) in Japan. Five main fault parameters of the area of the entire fault S, the averaged stress drop Δσ, the area of the asperities Sasp, the stress drop on the asperities Δσasp, and the short-period level A were determined by the two theoretical relationships and the three empirical relationships among the six main fault parameters including the seismic moment M0.