5:15 PM - 6:45 PM
[U15-P37] Spatial characteristics of long-period ground motions caused by the 2024 Noto Peninsula earthquake
Keywords:The 2024 Noto Peninsula earthquake, Long-period ground motions
Strong motions and tsunamis due to the 2024 Noto Peninsula earthquake, which occurred on January 1st, 2024, at 16:10 [JST] (MJMA 7.6), caused significant damage primarily in the Noto region of Ishikawa Prefecture. Significant long-period ground motions were also observed during this event. The JMA observed class 4 of long-period ground motions in the Noto region, and class 3 across Niigata, Ishikawa, Toyama, and Nagano Prefectures. This study investigates the spatial characteristics of the long-period ground motions due to this earthquake, particularly in Ishikawa, Toyama, and Niigata Prefectures. We calculated the pseudo velocity response spectrum (pSv) for 5% damping from the horizontal two-component records of strong-motion waveforms at K-NET and KiK-net stations of NIED, and examined the dominant period and peak value of pSv at each observed station.
At observed stations near the source fault in the Noto region in Ishikawa Prefecture, large values of pSv were observed with dominant periods of 1-3 s. The pSv at K-NET Shoin (ISK002) had a peak of approximately 580 cm/s at a period of approximately 3 s. Their intensity levels of long-period ground motions mostly fell within the standard-deviation range of prediction based on an existing distance-attenuation equation. At K-NET Hakui (ISK008), located within the Ouchi-gata Plain in the central part of Ishikawa Prefecture, pSv over 200 cm/s were observed at the period of approximately 4.5 s. This was significantly larger than the prediction from the distance-attenuation equation. K-NET Komatsu (ISK011) and K-NET Kaga (ISK014), located in the southern part of the Kanazawa Plain in Ishikawa Prefecture, observed pSvs peaking at a period of approximately 1 s, with peak values of approximately 90 cm/s and 130 cm/s, respectively.
The Tonami and Toyama Plains in Toyama Prefecture are composed of thick sedimentary layers several kilometers thick. Observed stations located in these plains, approximately 50-70 km from the source fault, had pSv exceeding or close to 100 cm/s, with dominant periods of 4-8 s. For example, K-NET Shinminato (TYM005) has pSv with a peak of approximately 120 cm/s at a period of approximately 6 s. The observed pSv values at these stations largely exceeded the prediction from the existing distance-attenuation equation, approaching the observed values of pSv with periods of 4-8 s near the source fault. K-NET Himi (TYM002) observed pSv with a peak of approximately 170 cm/s at a period of approximately 2 s.
The observed pSv at K-NET Niigata (NIG010), located in the central part of the Echigo Plain in Niigata Prefecture, had two peaks at periods of approximately 2 and 8 s, with both peaks of approximately 50 cm/s. This twin-peak pSv was also observed at other stations across the Niigata Plain (e.g., KiK-net Seiro (NIGH05), KiK-net Arakawa (NIGH03)). In the velocity waveform records at NIG010, we found the main part of the S-wave with a dominant period of approximately 2 s, followed by later phases with a dominant period of approximately 8 s. The observation of these notable later phases at observed stations in the Echigo Plain and Sado Island suggests the generation and amplification of later phases before entering the Echigo Plain, further amplified by the sedimentary structure of the Echigo Plain. Similar later phases were also observed during the May 5, 2023 (MJMA 6.5) earthquake in the Noto region. K-NET Kashiwazaki (NIG018) had pSv with a peak around 1.4 s of approximately 100 cm/s, and K-NET Naoetsu (NIG025), located in the Takada Plain, observed pSv peak near 0.7 s of approximately 210 cm/s.
We will also present the comparison with observed records of M~6 events and the seismic-wave propagation simulation.
At observed stations near the source fault in the Noto region in Ishikawa Prefecture, large values of pSv were observed with dominant periods of 1-3 s. The pSv at K-NET Shoin (ISK002) had a peak of approximately 580 cm/s at a period of approximately 3 s. Their intensity levels of long-period ground motions mostly fell within the standard-deviation range of prediction based on an existing distance-attenuation equation. At K-NET Hakui (ISK008), located within the Ouchi-gata Plain in the central part of Ishikawa Prefecture, pSv over 200 cm/s were observed at the period of approximately 4.5 s. This was significantly larger than the prediction from the distance-attenuation equation. K-NET Komatsu (ISK011) and K-NET Kaga (ISK014), located in the southern part of the Kanazawa Plain in Ishikawa Prefecture, observed pSvs peaking at a period of approximately 1 s, with peak values of approximately 90 cm/s and 130 cm/s, respectively.
The Tonami and Toyama Plains in Toyama Prefecture are composed of thick sedimentary layers several kilometers thick. Observed stations located in these plains, approximately 50-70 km from the source fault, had pSv exceeding or close to 100 cm/s, with dominant periods of 4-8 s. For example, K-NET Shinminato (TYM005) has pSv with a peak of approximately 120 cm/s at a period of approximately 6 s. The observed pSv values at these stations largely exceeded the prediction from the existing distance-attenuation equation, approaching the observed values of pSv with periods of 4-8 s near the source fault. K-NET Himi (TYM002) observed pSv with a peak of approximately 170 cm/s at a period of approximately 2 s.
The observed pSv at K-NET Niigata (NIG010), located in the central part of the Echigo Plain in Niigata Prefecture, had two peaks at periods of approximately 2 and 8 s, with both peaks of approximately 50 cm/s. This twin-peak pSv was also observed at other stations across the Niigata Plain (e.g., KiK-net Seiro (NIGH05), KiK-net Arakawa (NIGH03)). In the velocity waveform records at NIG010, we found the main part of the S-wave with a dominant period of approximately 2 s, followed by later phases with a dominant period of approximately 8 s. The observation of these notable later phases at observed stations in the Echigo Plain and Sado Island suggests the generation and amplification of later phases before entering the Echigo Plain, further amplified by the sedimentary structure of the Echigo Plain. Similar later phases were also observed during the May 5, 2023 (MJMA 6.5) earthquake in the Noto region. K-NET Kashiwazaki (NIG018) had pSv with a peak around 1.4 s of approximately 100 cm/s, and K-NET Naoetsu (NIG025), located in the Takada Plain, observed pSv peak near 0.7 s of approximately 210 cm/s.
We will also present the comparison with observed records of M~6 events and the seismic-wave propagation simulation.