Multi-Mode Surface Wave Inversion of the Kanto Sedimentary Basin

Session: Advances in Upper Crustal Geophysical Characterization [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Metropolitan Tokyo is subject to significant seismic hazards because it is located near two plate boundaries and because it sits atop soft and thick sediments of the Kanto Basin. Numerical simulations of earthquake ground motions rely on accurate velocity models of the basin elastic and anelastic structure, which remains to be improved. Here, we construct a high-resolution velocity model of the basin. To do this, we analyze seismic noise data recorded by 296 stations from the Metropolitan Seismic Observation network (MeSO-net) in 2012 and retrieved over 43,000 cross-correlation functions between the station pairs at the ZZ, RR and TT components. The functions exhibit clear energy from fundamental and first-overtone surface waves, whose dispersion information is extracted using the frequency-wavenumber (f-k) method based on correlation functions stacked within a 10 km radius of each station. The measured phase velocities from the two modes at 0.5-8 s period are used to invert for the averaged 1D structure including both the shear wave velocity and basin depth through a statistical Markov chain Monte Carlo approach (Shen et al., 2012). The 1D model is then combined to form a 3D shear-wave velocity model. We found that the multi-mode dispersion data can be fitted well using isotropic parameterization and that anisotropy was not necessary at this spatial resolution. The final 3D model shows consistency of the basin depth with the reference Japan Integrated Velocity Structure Model (JIVSM; Koketsu et al., 2008), which is constrained from multiple geophysical data. However, it also exhibits fine details, such as the transition of relatively faster velocities in the western part of the basin compared to the east at shallow depth to slower velocities at deeper depth. The implication of the new 3D velocity model on the basin evolution will also be discussed.

Presenting Author: Chengxin Jiang

Authors