9:00 AM - 9:15 AM
[SSS11-06] Aftershock observations for the 2024 Noto Peninsula earthquake at Ukawa district of Noto town
Keywords:The 2024 Noto Peninsula earthquake, Ukawa area of Noto town, aftershock observation, earthquake disaster, velocity structure
The 2024 Noto Peninsula Earthquake caused damage including collapsed houses in the Ukawa district of Noto Town, Ishikawa Prefecture, Japan. The collapse of houses was concentrated in the sedimentary lowlands near the coast and was minor in the surrounding foothills. Three-component aftershock observation was carried out at Ukawa Elementary School in the foothills and Ukawa Community Center in the sedimentary layer area using a velocity type seismometer KVS-300 manufactured by Kinkei System Corporation and a 24-bit data logger HKS-9700 by NF Keisokugiken Corporation for a period of about two months from September 12th to November 6th, 2024. As a result, simultaneously recorded data of 9 earthquakes with JMA seismic intensity of 2 to 3 within the target area were obtained at both sites.
The horizontal/vertical spectral ratios of the obtained earthquake data (EHVSR) are shown in the figure. The figure shows the EHVSR calculated for each NS and EW component and the geometric average of the horizontal component. At Ukawa Elementary School, located at the foot of the mountain, the EHVSR has a peak around the period of 0.33 s with approximately twice in ratio, and is almost flat with ratio one in longer period range over 1 s. It corresponds to the hard ground. On the other hand, at Ukawa Community Center, there is a large peak around 0.9 s, and small peaks are also noticed around 0.2 s and 0.3 s. Although no records of the main shock have been obtained in the Ukawa district, it is suggested that the predominant period around 0.3 s, which is the natural period of a typical wooden house, may have been amplified in the sedimentary layer around the Ukawa Community Center, and there is a concern that the natural period of those houses with low earthquake resistance could become longer due to damage. Furthermore, it is suggested that damage ranging from severe to collapse may have occurred due to the amplification at around 0.9 s. The horizontal/vertical spectral ratio of the microtremors (MHVSR) observed in the damaged areas was found to be in the range of 0.6 to 1.0 s, suggesting that the process described above led to the housing damage. We would like to identify an underground velocity structure model that satisfies the obtained EHVSR using diffuse field theory (Kawase et al., 2011) and consider the relationship between velocity structure and damage.
We would like to thank Ukawa Elementary School and Ukawa Community Center for their assistance in installing seismometers. Prof. Nishikawa H of Fukui University of Technology provided his damage survey report. This study was supported by Tokio Marine Kagami Memorial Foundation and the Third Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research) by MEXT.
Reference: Kawase et al., 2011, Bull. Seism. Soc. Am., 101(5), 2001-2014.
The horizontal/vertical spectral ratios of the obtained earthquake data (EHVSR) are shown in the figure. The figure shows the EHVSR calculated for each NS and EW component and the geometric average of the horizontal component. At Ukawa Elementary School, located at the foot of the mountain, the EHVSR has a peak around the period of 0.33 s with approximately twice in ratio, and is almost flat with ratio one in longer period range over 1 s. It corresponds to the hard ground. On the other hand, at Ukawa Community Center, there is a large peak around 0.9 s, and small peaks are also noticed around 0.2 s and 0.3 s. Although no records of the main shock have been obtained in the Ukawa district, it is suggested that the predominant period around 0.3 s, which is the natural period of a typical wooden house, may have been amplified in the sedimentary layer around the Ukawa Community Center, and there is a concern that the natural period of those houses with low earthquake resistance could become longer due to damage. Furthermore, it is suggested that damage ranging from severe to collapse may have occurred due to the amplification at around 0.9 s. The horizontal/vertical spectral ratio of the microtremors (MHVSR) observed in the damaged areas was found to be in the range of 0.6 to 1.0 s, suggesting that the process described above led to the housing damage. We would like to identify an underground velocity structure model that satisfies the obtained EHVSR using diffuse field theory (Kawase et al., 2011) and consider the relationship between velocity structure and damage.
We would like to thank Ukawa Elementary School and Ukawa Community Center for their assistance in installing seismometers. Prof. Nishikawa H of Fukui University of Technology provided his damage survey report. This study was supported by Tokio Marine Kagami Memorial Foundation and the Third Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research) by MEXT.
Reference: Kawase et al., 2011, Bull. Seism. Soc. Am., 101(5), 2001-2014.