4:30 PM - 4:45 PM
[HDS10-11] The Increase of Tsunami Height in the Distant Area of the Wave Source of the 2024 Noto Peninsula Earthquake Tsunami
Keywords:2024 Noto Peninsula Earthquake, scattering, edge wave, Hegurajima
Introduction
On January 1, 2024, a Mw 7.5 earthquake occurred in the Noto Peninsula, generating tsunamis observed across a wide area along the Sea of Japan coast. Several studies have investigated the tsunami generation mechanisms associated with this event (e.g., Satake et al., 2024; Masuda et al., 2024). Arikawa et al. (2024) suggested that the locally high tsunami waves observed in Joetsu City and Sado Island could be explained by the rupture of partial faults within the F43 and F42 fault models proposed by the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT, 2014). Furthermore, Kurihara et al. (2024) demonstrated that considering both fault rupture and submarine landslides could account for the observed waveforms in Joetsu City and the tsunami trace heights along the Niigata and Sado Island coastlines. However, along the northern Tohoku and Sanin coastal areas, the maximum tsunami amplitudes were observed more than three hours after the earthquake; however, the cause of this phenomenon remains unclear. Therefore, this study aims to clarify the generation process of the maximum tsunami amplitudes during later phases at distant locations from the tsunami source through numerical tsunami simulations spanning a wide area from Akita Prefecture to Tottori Prefecture.
Methodology
In this study, numerical tsunami simulations were conducted for a wide area along the Sea of Japan coast, from Akita Prefecture to Tottori Prefecture. The tsunami simulations were conducted using JAGURS (Baba et al., 2019). The bathymetric model by No et al. (2016) was used, with a spatial grid resolution of 6 seconds. The computational domain was defined with the southwestern boundary at (35.35°N, 132.48°E) and the northeastern boundary at (41.2705°N, 140.6305°E). The fault model proposed by Arikawa et al. (2024) was adopted. To analyze the tsunami later phase observed in Akita and Tottori Prefectures, we simulated for 24 hours. The simulation results were compared with observational data obtained from the Nationwide Ocean Wave Information Network for Ports and Harbors (NOWPHAS).
Results
The waveform observed at the NOWPHAS wave gauge in Akita showed that the first wave (approximately 6 cm) arrived at around 17:25, followed by the second wave (approximately 12 cm) at around 17:45. The largest tsunami wave occurred three hours after the earthquake, reaching about 14 cm at around 19:30. At the NOWPHAS wave gauge in Tottori, the first wave (approximately 4 cm) was observed at around 17:20, followed by the third wave (approximately 10 cm) at around 18:45. The largest tsunami wave in Tottori was observed four hours after the earthquake, reaching approximately 27 cm at around 20:40. These observations indicate that, in both Akita and Tottori, the amplitudes of the later waves were larger than that of the first wave. The numerical simulation results suggest that the increased amplitude of the second wave compared to the first wave was influenced by backscatter effects from Hegurajima Island, located north of the Noto Peninsula. The backscattered waves generated by the topography around Hegurajima reached Akita approximately 100 minutes later and Tottori approximately 150 minutes later. These arrival times approximately match the peaks of the second wave in Akita and the third wave in Tottori. Regarding the maximum tsunami amplitudes observed more than three hours after the earthquake, edge waves propagating along the coastline were likely generated due to the bathymetric characteristics. Additionally, wave reflections caused by the curved coastal shapes of areas such as the Oga Peninsula and Sakai Port contributed to wave superposition, resulting in an amplified tsunami amplitude.
Conclusion
This study investigated the factors contributing to the amplification of later tsunami waves in distant areas from the tsunami source. The numerical simulation results spanning a wide area along the Sea of Japan coast suggest that the second and third waves in Akita and Tottori were significantly influenced by wave scattering from Hegurajima Island. Additionally, the increase in tsunami amplitude observed 3–5 hours after the earthquake was likely due to the excitation of edge waves and their superposition with reflected waves.
On January 1, 2024, a Mw 7.5 earthquake occurred in the Noto Peninsula, generating tsunamis observed across a wide area along the Sea of Japan coast. Several studies have investigated the tsunami generation mechanisms associated with this event (e.g., Satake et al., 2024; Masuda et al., 2024). Arikawa et al. (2024) suggested that the locally high tsunami waves observed in Joetsu City and Sado Island could be explained by the rupture of partial faults within the F43 and F42 fault models proposed by the Ministry of Land, Infrastructure, Transport, and Tourism (MLIT, 2014). Furthermore, Kurihara et al. (2024) demonstrated that considering both fault rupture and submarine landslides could account for the observed waveforms in Joetsu City and the tsunami trace heights along the Niigata and Sado Island coastlines. However, along the northern Tohoku and Sanin coastal areas, the maximum tsunami amplitudes were observed more than three hours after the earthquake; however, the cause of this phenomenon remains unclear. Therefore, this study aims to clarify the generation process of the maximum tsunami amplitudes during later phases at distant locations from the tsunami source through numerical tsunami simulations spanning a wide area from Akita Prefecture to Tottori Prefecture.
Methodology
In this study, numerical tsunami simulations were conducted for a wide area along the Sea of Japan coast, from Akita Prefecture to Tottori Prefecture. The tsunami simulations were conducted using JAGURS (Baba et al., 2019). The bathymetric model by No et al. (2016) was used, with a spatial grid resolution of 6 seconds. The computational domain was defined with the southwestern boundary at (35.35°N, 132.48°E) and the northeastern boundary at (41.2705°N, 140.6305°E). The fault model proposed by Arikawa et al. (2024) was adopted. To analyze the tsunami later phase observed in Akita and Tottori Prefectures, we simulated for 24 hours. The simulation results were compared with observational data obtained from the Nationwide Ocean Wave Information Network for Ports and Harbors (NOWPHAS).
Results
The waveform observed at the NOWPHAS wave gauge in Akita showed that the first wave (approximately 6 cm) arrived at around 17:25, followed by the second wave (approximately 12 cm) at around 17:45. The largest tsunami wave occurred three hours after the earthquake, reaching about 14 cm at around 19:30. At the NOWPHAS wave gauge in Tottori, the first wave (approximately 4 cm) was observed at around 17:20, followed by the third wave (approximately 10 cm) at around 18:45. The largest tsunami wave in Tottori was observed four hours after the earthquake, reaching approximately 27 cm at around 20:40. These observations indicate that, in both Akita and Tottori, the amplitudes of the later waves were larger than that of the first wave. The numerical simulation results suggest that the increased amplitude of the second wave compared to the first wave was influenced by backscatter effects from Hegurajima Island, located north of the Noto Peninsula. The backscattered waves generated by the topography around Hegurajima reached Akita approximately 100 minutes later and Tottori approximately 150 minutes later. These arrival times approximately match the peaks of the second wave in Akita and the third wave in Tottori. Regarding the maximum tsunami amplitudes observed more than three hours after the earthquake, edge waves propagating along the coastline were likely generated due to the bathymetric characteristics. Additionally, wave reflections caused by the curved coastal shapes of areas such as the Oga Peninsula and Sakai Port contributed to wave superposition, resulting in an amplified tsunami amplitude.
Conclusion
This study investigated the factors contributing to the amplification of later tsunami waves in distant areas from the tsunami source. The numerical simulation results spanning a wide area along the Sea of Japan coast suggest that the second and third waves in Akita and Tottori were significantly influenced by wave scattering from Hegurajima Island. Additionally, the increase in tsunami amplitude observed 3–5 hours after the earthquake was likely due to the excitation of edge waves and their superposition with reflected waves.