11:00 AM - 1:00 PM
[SSS10-P09] Modeling of Subsurface Velocity Structures from Seismic Bedrock to Ground Surface for a Strong Ground Motion Prediction in the Yamanashi Region.
Keywords:underground structure model, strong ground motion, microtrmors, s-wave velocity, gravity
The NIED has developed a shallow and deep integrated underground structure model for strong ground motion prediction based on the "concept of underground structure model creation" as part of the creation of the "national seismic motion prediction map" of the Headquarters for Earthquake Research Promotion(HERP). So far, it has been created using the S-wave velocity structure with a large amount of microtremor observation data (about 26,000 small arrays and about 750 large arrays) carried out in the Kanto, Tokai, and Kumamoto regions. Since then, we have continued to conduct exploration in the areas around Kanto and Tokai (Yamanashi, Nagano, Fukushima, etc.). By using these data, we have greatly improved the conventional underground structure model construction method. It has become possible to construct a underground structure model that can handle a wide area and a wide band from the earthquake base to the surface of the earth used for strong ground motion prediction (Senna et al., (2019), HERP 2017, 2021). A local underground model was released by the HERP and J-SHIS last year. In this study, we report on the construction of a underground structure model using microtremor observation data and seismic observation data in the entire Yamanashi region.
We conducted microtremor array observations (23 points) with a maximum radius of 400 m and analyzed them throughout Yamanashi prefecture, and estimated the phase velocity and H/V spectrum at each microtremor observation point. In addition, seismic records were collected and the R/V spectra for each seismic station were obtained using the collected seismic records. Furthermore, small array exploration was conducted mainly to confirm shallow underground structure models and the top surface of engineering bedrock. It was carried out at 741 points, and the phase velocity and S-wave velocity structures were analyzed. The microtremor array and seismic observation points used are shown in Fig. 1. The obtained phase velocity, H/V spectrum, and R/V spectrum are shown. Based on this, an inverse analysis (Suzuki and Yamanaka, 2010) was performed, the S-wave velocity structure for each point was estimated, and the deep underground structure model (J-SHIS_V2) currently published by J-SHIS was modified.
Compared to the model before modification, the deep underground structure model after modification is deeper after modification in the entire Kofu basin from the engineering bedrock to the Vs 900 m/s layer. Also, the Vs 1,200 m/s layer in the deeper part, it tended to be shallower after correction on the northwest side of the basin and deeper on the east side.
In this study, we will construct a underground structure model that is more harmonious with the seismic observation record by estimating the S wave velocity structure and modifying the ground model by inverse analysis using microtremor observation and seismic observation data of the entire Yamanashi region. In the future, we plan to verify the accuracy of the model by the three-dimensional difference method after connecting it to the underground structure models in the Kanto and Tokai regions.
We conducted microtremor array observations (23 points) with a maximum radius of 400 m and analyzed them throughout Yamanashi prefecture, and estimated the phase velocity and H/V spectrum at each microtremor observation point. In addition, seismic records were collected and the R/V spectra for each seismic station were obtained using the collected seismic records. Furthermore, small array exploration was conducted mainly to confirm shallow underground structure models and the top surface of engineering bedrock. It was carried out at 741 points, and the phase velocity and S-wave velocity structures were analyzed. The microtremor array and seismic observation points used are shown in Fig. 1. The obtained phase velocity, H/V spectrum, and R/V spectrum are shown. Based on this, an inverse analysis (Suzuki and Yamanaka, 2010) was performed, the S-wave velocity structure for each point was estimated, and the deep underground structure model (J-SHIS_V2) currently published by J-SHIS was modified.
Compared to the model before modification, the deep underground structure model after modification is deeper after modification in the entire Kofu basin from the engineering bedrock to the Vs 900 m/s layer. Also, the Vs 1,200 m/s layer in the deeper part, it tended to be shallower after correction on the northwest side of the basin and deeper on the east side.
In this study, we will construct a underground structure model that is more harmonious with the seismic observation record by estimating the S wave velocity structure and modifying the ground model by inverse analysis using microtremor observation and seismic observation data of the entire Yamanashi region. In the future, we plan to verify the accuracy of the model by the three-dimensional difference method after connecting it to the underground structure models in the Kanto and Tokai regions.