[S-SS10] Strong Ground Motion and Earthquake Disaster

[SSS10-P15] A study for reconstructing three-dimensional velocity structure model in Tottori plain

*Takao Kagawa¹, Nao Tanigawa², Tatsuya Noguchi¹ (1.Tottori University, Faculty of Engineering, 2.Tottori University, Graduate School of Sustainability Science, Department of Engineering)

Keywords:Tottori plain, three-dimensional velocity structure, earthquake ground motion, microtremor survey, gravity anomaly

An updated three-dimensional velocity structure model in Tottori plain from the previous model (Tottori prefecture, 2018) is reported. We have reconstructed the model from the reanalysis of observed small earthquake records, microtremor survey data, and gravity survey data in the target area. First, we constructed velocity structure models with common physical properties of sedimentary layers using the diffuse field theory (Kawase et al., 2011), in order to satisfy the EHVSRs (H/V spectrum ratio of earthquake ground motions) obtained at earthquake observation sites in Tottori plain. Referring to the obtained results, deep velocity structure models were estimated to satisfy the phase velocity dispersion curve from large scale microtremor array data and simultaneously observed predominant periods of MHVSRs (H/V of microtremor). The results suggest that the depths of the layer boundaries are roughly proportional to the basement depth, and that there is a common tendency in the distribution of gravity anomalies and the distribution of a layer boundary depth from microtremors. Using the shape of the gravity anomaly distribution from more detailed observation, the basement shape was interpolated using RBF (Radial Basis Function), which is generally used for interpolation of pointcloud survey data in computer graphics. After confirming that the estimated model reproduces well the observed characteristics of earthquakes and microtremors, we are attempting to reproduce the observed waveforms at ground motion observation sites.
This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under its The Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research).
References: Kawase et al.,2011, BSSA, 101(5), 2001-2014. Tottori Prefecture Earthquake Disaster Prevention Report, 2018.