Misidentification caused by leaky surface wave in high-frequency surface wave method

Accurate computation of leaky modes for anomalous layered models

“…Next, we conduct the computation of leaky modes for the three-layer model by Gao et al [2014] which contains a low-velocity half-space. The normal modes (represented by solid dots in Figure 2) are absent in the frequency range from ~0.6 Hz to ~22 Hz.…”

“…For models typically with high Poisson's ratios such as that shown in Table 1, leaky waves may show significant energy on the seismogram recorded at proper distances [Roth et al 1998, Gao et al 2014. Dispersion analysis in terms of mode theory would then afford complementary information for seismic surveying, especially for inverting the P-wave velocity structure [Oliver 1964, Su and Dorman 1965, Znak and Kashtan 2015 due to it being better sensed by leaky modes than by shear normal modes.…”

“…Earth's surface is often covered by unconsolidated sediments characterized by high Poisson's ratios [Stüm-pel et al 1984, Roth et al 1998, Gao et al 2014, and thus the layer boundaries are commonly associated with a strong velocity contrast. Leaky waves, which can be regarded as the superposition of leaky modes [Haddon 1984], are therefore evident in the early arrivals [Roth et al 1998, Gao et al 2014; in certain cases, slowly-attenuating leaky waves of phase velocities faster than S waves in the half-space may exist, which correspond to real frequency and real wavenumber pairs [García-Jerez and Sánchez-Sesma 2015].…”

“…Leaky waves, which can be regarded as the superposition of leaky modes [Haddon 1984], are therefore evident in the early arrivals [Roth et al 1998, Gao et al 2014; in certain cases, slowly-attenuating leaky waves of phase velocities faster than S waves in the half-space may exist, which correspond to real frequency and real wavenumber pairs [García-Jerez and Sánchez-Sesma 2015].…”

“…The presence of leaky waves may either cause difficulty in correctly identifying dispersion curves of normal modes so that the final inverted S-wave velocity model could deviate from the true model [Gao et al 2014], or constructively afford useful information for characterizing P-wave velocity structure [Su and Dorman 1965] or for performing full-waveform inversions [Roth et al 1998], and also help fill in the gaps of Rayleigh dispersion curves of normal modes for models with the half-space being a low-velocity layer [Yang and Yi 2005].…”