2025 Volume 25 Issue 12 Pages 12_76-12_91
During the 2024 Noto Peninsula earthquake, significant long-period ground motions were observed not only in the Noto region of Ishikawa Prefecture near the earthquake source region, but also over a wide area in the Hokuriku region. To clarify the characteristics of these long-period ground motions, we analyzed the strong-motion records obtained from K-NET and KiK-net of the National Research Institute for Earth Science and Disaster Resilience. We found that large pseudo velocity response spectra with a peak period of 1-3 s were observed at many stations in the Noto region, while pseudo velocity response spectra observed at stations in the Echigo Plain of Niigata Prefecture and the Toyama Plain of Toyama Prefecture were comparable to those near the earthquake source region at periods of 4 s or longer. In the Echigo Plain, the pronounced long-period ground motions peaking around 8 s are inferred to result from Rayleigh waves that were generated and amplified near the source and/or during propagation, and subsequently further amplified by the thick sedimentary layers underlying the plain. Moreover, long-period ground motions in the Toyama Plain are considered to be primarily attributable to the superposition of multiple surface waves arriving from different directions and at different times, which were further amplified and temporally prolonged by the subsurface structure of the sedimentary plain.
