Fig. 12

Multicomponent frequency–Bessel spectrograms of field data in North America. a–d are the FJ spectrograms \(I_{R0}\), \(I_{R1}\), \(I_{R2}\), and \(I_{L0}\), respectively. Here, \(I_{R0}\) is FJ spectrum of Rayleigh wave using ZZ components, \(I_{R1}\) is FJ spectrum of Rayleigh wave using RZ and ZR components, \(I_{R2}\) is FJ spectrum of Rayleigh wave using RR and TT components, and \(I_{L0}\) is FJ spectrum of Love wave using RR and TT components. The black arrow in (a) indicates the location where the fundamental mode Rayleigh wave is bifurcated into two branches. The ith overtone is labeled next to each dispersion curve, and 0 indicates the fundamental mode. Taken from Hu et al. (2020)