2025 Volume 25 Issue 4 Pages 4_196-4_205
Blind faults, which cannot be identified in advance, in/on the Philippine Sea plate and the Pacific Sea plate affect greatly for seismic hazard in the Tokyo metropolitan area (NIED, 2023). Basic idea of performance-based design (JSCA, 2018) is that seismic damages are controlled by strong ground motions corresponding to some representative recurrence periods. So, the relation between intensity of ground motions and recurrence periods must be precisely known. In this study, we evaluated velocity response spectrum at Shinjuku corresponding its recurrence periods of 500, 1000, 2500 years by blind faults in/on the Philippine Sea plate and the Pacific Sea plate near the Kanto area. The velocity response spectrum for recurrence period of 1000 years was 80 – 110 cm/s and predominated at periods of 2 s and 7.5 s. These predominancies were due to S-wave amplification of the layers above the layer with S-wave velocity of 1.5 km/s and the seismic bedrock respectively. Peak amplitudes at 2s and 7s were about 10% and 4% bigger than average amplitudes of the nearby periods.
