11:00 AM - 1:00 PM
[SSS10-P11] Estimation of Subsurface Structures and Ground Motion Characteristics in the Landslide Areas from Microtremor and Earthquake Observations – Saji-cho, Tottori City –
Keywords:Microtremor observation, H/V spectra, Landslide, Subsurface structure
In recent years, large-scale landslide damages due to the earthquakes have been caused, such as the 2009 Sumatra Earthquake and the 2018 Hokkaido Iburi East Earthquake,
where strong ground motions affected. These areas contain volcanic ash layers and weathered rock that might have accumulated by repeated landslides in the past. This suggests that strong ground motions is a key trigger of widespread landslides. Then estimation of the underground structure in landslide areas is very important issue for evaluating risk of slope hazards. In this study, we conducted microtremor and continuous earthquake observations in the area around
Takayama, Saji-cho, Tottori City, Tottori Prefecture, based on the landslide topography map published by the National Research Institute for Earth Science and Disaster Prevention (NIED). The data were analyzed to understand the ground motion characteristics of the landslide area and to estimate the subsurface structures.
According to the surface geology map of Takayama, Saji-cho, phyllites are covered by Neogene volcanic rocks, and the designated landslide area consists mainly of gravel, sand and clay. In the area, 49 single-point observations and 3 array observations were conducted by Noguchi et al. (2021). In this study, 46 single-point observations and one array observation were additionally conducted. The data were analyzed also with the previous data. For the continuous observation, a seismometer has been installed on the foundation of an astronomical observatory, the Saji Astro-park in Tottori City, since August 11, 2021.
The results shows that the predominant period of microtremor H/V spectra ratios are in the range of 0.01-0.80 seconds, and predominant periods within a specific range are concentrated and distributed in certain areas, regardless of the landslide bodies or sliding cliffs. From the microtremor array observation, several meters of low velocity layers with S-wave velocities of 100-200 m/s were estimated in the shallowest layer. The S-wave velocities of the landslide bodies were evaluated as 300-450 m/s, and the thickness of the layers were about 25 m from the S-wave velocities and the predominant periods. It is found that the thickness of landslide layer gradually increases from the slide cliffs to the landslide edges. From the H/V spectra obtained by several earthquake records, we confirmed a predominant peak at 0.75 seconds in the longer period than the peak at 0.20 seconds from the microtremor observation. It is assumed that the peak on the longer period side is affected by the deep structures under the landslide bodies.
where strong ground motions affected. These areas contain volcanic ash layers and weathered rock that might have accumulated by repeated landslides in the past. This suggests that strong ground motions is a key trigger of widespread landslides. Then estimation of the underground structure in landslide areas is very important issue for evaluating risk of slope hazards. In this study, we conducted microtremor and continuous earthquake observations in the area around
Takayama, Saji-cho, Tottori City, Tottori Prefecture, based on the landslide topography map published by the National Research Institute for Earth Science and Disaster Prevention (NIED). The data were analyzed to understand the ground motion characteristics of the landslide area and to estimate the subsurface structures.
According to the surface geology map of Takayama, Saji-cho, phyllites are covered by Neogene volcanic rocks, and the designated landslide area consists mainly of gravel, sand and clay. In the area, 49 single-point observations and 3 array observations were conducted by Noguchi et al. (2021). In this study, 46 single-point observations and one array observation were additionally conducted. The data were analyzed also with the previous data. For the continuous observation, a seismometer has been installed on the foundation of an astronomical observatory, the Saji Astro-park in Tottori City, since August 11, 2021.
The results shows that the predominant period of microtremor H/V spectra ratios are in the range of 0.01-0.80 seconds, and predominant periods within a specific range are concentrated and distributed in certain areas, regardless of the landslide bodies or sliding cliffs. From the microtremor array observation, several meters of low velocity layers with S-wave velocities of 100-200 m/s were estimated in the shallowest layer. The S-wave velocities of the landslide bodies were evaluated as 300-450 m/s, and the thickness of the layers were about 25 m from the S-wave velocities and the predominant periods. It is found that the thickness of landslide layer gradually increases from the slide cliffs to the landslide edges. From the H/V spectra obtained by several earthquake records, we confirmed a predominant peak at 0.75 seconds in the longer period than the peak at 0.20 seconds from the microtremor observation. It is assumed that the peak on the longer period side is affected by the deep structures under the landslide bodies.