Achievements of strong motion seismology in 20 century and its future directions

We have been trying to make a recipe for predicting ground motions from future large earthquakes. To do that the most important factors are the source characterizations for complex rupture processes and the Green’s function estimations for realistic geological structures. We attempt to formulate the source characterizations based on recent results of the waveform source inversion. There are two important aspects of characterizing the earthquake sources, outer and inner source parameters. The outer source parameters such as total fault length, width, seismic moment and so on are obtainable based on geological investigations of capable earthquake faults and seismological studies of source models. The inner source parameters are parameters related to slip heterogeneity on fault plane from the waveform inversion of strong motion records. We find that the areas of large slip known as asperities follow a self-similar scaling as well as the total rupture areas from the statistical analysis of the inverted results. This implies that both parameters, outer and inner ones, are predictable. Based on the results above mentioned we construct the procedure of characterizing the source for scenario earthquakes compiling accumulated knowledge about earthquake faults in geomorphology and seismology. We have examined the procedure comparing between observed records and synthetic ground motions from the characterized sources based on kinematic models for the recent large earthquakes. Then, we have confirmed the validity of the procedures for characterizing the earthquake sources and calculating ground motions. In future directions, the validity and applicability of predicting strong ground motions should be made taking into account source dynamics physically realizable. For example, surface displacements for the above model should be estimated from dynamic rupture process, assuming additional source parameters such as critical slip and strength excess for dynamic source simulation and compared with observed ones from geological and geomorphological survey.