Automatic generation system of subsurface structure models by micro-tremor observation

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In order to prevent or mitigate future earthquake disasters, precise subsurface structure models are most effective to improve earthquake risk analysis and earthquake ground motion estimates. Micro-tremor observation, which is handy and inexpensive, can be used to construct subsurface structure models ; however, micro-tremor is composed of various waves and should be supplemented by other information to construct a proper subsurface model. In this study, systematic search algorithm for an optimal subsurface model is sought, which utilizes an inverse analysis for H/V spectra and dispersion curves obtained by micro-tremor array observation.First, we were equipped with seven portable seismographs to carry out array observation with FK analysis at Higashi-shinagawa in Tokyo and Kohoku in Yokohama, and also at Ojiya and Tokamachi where strong ground motion was observed during Niigataken Chuetsu earthquake. Parallel to these observations, we have developed inverse algorithm for multiple targets with the Neighbourhood algorithm, as well as a computer program for calculating surface wave velocities fast and stable with generalized TR matrix method up to higher Rayleigh wave normal modes.We have,done joint inversion at those four sites and have shown the effectiveness of incorporating information of deeper layer interfaces retained in H/V spectra to that of precise shallower layering reflected in dispersion curves to improve subsurface models up to the depth of several tens of meters with urbanely realistic array radius of less than 100 meters.