Multimodal Rayleigh and Love Wave Joint Inversion for S-Wave Velocity Structures in Kanto Basin, Japan

Prevention of earthquake disaster is critical in the densely populated Kanto Basin, Japan, because of the presence of thick sediments that amplify strong ground motion. For this, a high-resolution three-dimensional S-wave velocity model is essential to understand the complex amplification of strong ground motion. We constructed a three-dimensional S-wave velocity model using the joint inversion of multimodal dispersion curves of Rayleigh and Love waves. Inclusion of higher modes significantly improved the accuracy and precision of the surface-wave inversion by more than 50% compared to using only fundamental mode. Our proposed model revealed a low-velocity anomaly of sediments toward the east and a curved velocity contour of the basement rock, thereby better explaining the observed complex surface-wave dispersion curves that have been unexplained in past homogeneous multilayered models. Estimated S-wave velocity model better reflected subsurface heterogeneity, providing vital information for hazard assessment in a metropolitan area where huge earthquakes are expected.