5:15 PM - 6:30 PM
[SCG40-P03] 3D velocity structure model of the Kathmandu valley for ground motion simulation
Keywords:3D velocity structure model, gravity survey, microtremor array, R/V spectral ratio, 3D finite-difference method
For evaluating seismic hazards in the Kathmandu valley after the 2015 Gorkha earthquqke, we are doing a joint research project with the Department of Mines and Geology, Nepal, under the SATREPS program of Japan Science and Technology Agency and Japan International Corporation Agency.
In this project, a 3D velocity structure model was constructed, using the results of reflection surveys (Kawasaki et al., 2019), boring explorations, microtremor surveys (Yokoi et al., 2019), gravity surveys (Pradhan et al., 2018), and R/V spectrum analyses. We performed joint inversion analysis of phase velocity and the R/V spectra (Senna et al,2013). We calculated phase velocity for fundamental mode. For theoretical H/V spectra, we calculated residuals with theoretical and observed values normalized to their maximum values to align peak shapes. We obtained theoretical H/V spectra of Rayleigh waves with medium response of Rayleigh waves of the fundamental to 4th mode (Arai and Tokimatsu, 2004). The correlation between the basement depth and the gravity basement elevation by reflection survey and inversion results of microtremor survey was abour 0.9.
We performed the Sequential Gaussian Co-simulation (Remy et al., 2009; Pyrcz and Deutsch, 2014) to combine and interpolate these results. The model consists of several layers, and the boundary shape of each layer was estimated in 50 cases by the Sequential Gaussian Co-simulation(Figure 1). They were then averaged to obtain the final boundary shape of each layer. To confirm the obtained model, we simulated ground motions for moderate earthquakes using the 3D finite difference method. The simulated ground velocity waveforms almost agree with observed waveforms.
In this project, a 3D velocity structure model was constructed, using the results of reflection surveys (Kawasaki et al., 2019), boring explorations, microtremor surveys (Yokoi et al., 2019), gravity surveys (Pradhan et al., 2018), and R/V spectrum analyses. We performed joint inversion analysis of phase velocity and the R/V spectra (Senna et al,2013). We calculated phase velocity for fundamental mode. For theoretical H/V spectra, we calculated residuals with theoretical and observed values normalized to their maximum values to align peak shapes. We obtained theoretical H/V spectra of Rayleigh waves with medium response of Rayleigh waves of the fundamental to 4th mode (Arai and Tokimatsu, 2004). The correlation between the basement depth and the gravity basement elevation by reflection survey and inversion results of microtremor survey was abour 0.9.
We performed the Sequential Gaussian Co-simulation (Remy et al., 2009; Pyrcz and Deutsch, 2014) to combine and interpolate these results. The model consists of several layers, and the boundary shape of each layer was estimated in 50 cases by the Sequential Gaussian Co-simulation(Figure 1). They were then averaged to obtain the final boundary shape of each layer. To confirm the obtained model, we simulated ground motions for moderate earthquakes using the 3D finite difference method. The simulated ground velocity waveforms almost agree with observed waveforms.