5:15 PM - 7:15 PM
[SSS11-P03] Microtremor Observations at Fault Displacement Sites of the Noto Peninsula
Earthquake - Wakayama, Suzu City and Tomirai District, Shiga Town
Keywords:Noto Peninsula Earthquake, fault displacement, Microtremor observation, Ground seismic characteristics, ground structure
On January 1, 2024, a magnitude 7.6 earthquake occurred in the Noto region of Ishikawa Prefecture. Along the Wakayama River in Wakayama-cho, Suzu City, Ishikawa Prefecture, a linear surface deformation with a maximum vertical displacement of approximately 2.2 m was observed, along with an uplift zone with a total length of approximately 4 km and a width of 100-200 m. In addition, along the south bank fault of the Tokugawa River in the northern part of Tokugawa, Shika-cho, Hakui County, an earthquake fault with a vertical displacement of 10 to several tens of cm and a left slip of 50 cm appeared on the southeast side.
In this study, we conducted dense microtremor observations in the vicinity of the confirmed fault displacement in Wakayama-cho, Suzu City and Tokugawa area, Shika-cho, where these surface deformations were observed, to grasp the ground vibration characteristics of the target points and estimate the ground structure, and consider the ground vibration characteristics and their causes near the fault.
Microtremor observations were performed using a three-component integrated accelerating seismometer (JU410), with array observations at surface displacement sites in an L-shape or straight line with a seismometer spacing of 1 to 40 m. Three-component single-point observations were also performed at 62 points across the wide area of Wakayama-cho, Suzu City, including the array observation data. In the Togi area of Shika-cho, data from 22 points was analyzed in addition to the array observations mentioned above. For the analysis, the array observation data was used to obtain phase velocity dispersion curves using the SPAC method to estimate a ground structure model. Furthermore, the three-component single-point observations were used to obtain H/V spectra, and continuous changes in the dominant period distribution and spectral shape were investigated.
In the Naka area of Wakayama-cho, Suzu City, the H/V spectrum showed peaks on the short period side (around 0.1 seconds) and long period side (around 2 seconds) in the immediate vicinity of the surface displacement site (fault), and it was observed that the dominant period changed rapidly from the north to the south of the fault. Additionally, anisotropy was observed in the horizontal component of the H/V spectrum north of the fault, with EW/UD being larger than NS/UD near the peak on the short-period side. Corresponding changes were also observed in the ground structure. In the Tomioka area of Shika Town, it was found that the dominant period of the H/V spectrum changes drastically from the south to the north of the fault line.
In this study, we conducted dense microtremor observations in the vicinity of the confirmed fault displacement in Wakayama-cho, Suzu City and Tokugawa area, Shika-cho, where these surface deformations were observed, to grasp the ground vibration characteristics of the target points and estimate the ground structure, and consider the ground vibration characteristics and their causes near the fault.
Microtremor observations were performed using a three-component integrated accelerating seismometer (JU410), with array observations at surface displacement sites in an L-shape or straight line with a seismometer spacing of 1 to 40 m. Three-component single-point observations were also performed at 62 points across the wide area of Wakayama-cho, Suzu City, including the array observation data. In the Togi area of Shika-cho, data from 22 points was analyzed in addition to the array observations mentioned above. For the analysis, the array observation data was used to obtain phase velocity dispersion curves using the SPAC method to estimate a ground structure model. Furthermore, the three-component single-point observations were used to obtain H/V spectra, and continuous changes in the dominant period distribution and spectral shape were investigated.
In the Naka area of Wakayama-cho, Suzu City, the H/V spectrum showed peaks on the short period side (around 0.1 seconds) and long period side (around 2 seconds) in the immediate vicinity of the surface displacement site (fault), and it was observed that the dominant period changed rapidly from the north to the south of the fault. Additionally, anisotropy was observed in the horizontal component of the H/V spectrum north of the fault, with EW/UD being larger than NS/UD near the peak on the short-period side. Corresponding changes were also observed in the ground structure. In the Tomioka area of Shika Town, it was found that the dominant period of the H/V spectrum changes drastically from the south to the north of the fault line.