The damping ratio is an important index used in soil nonlinearity studies and is mostly proportional to the shear strain increase. Previous researches indicated a frequency-independent damping in most cases. In this study, frequency-dependent damping was introduced from frequency-dependent Q calculated through the spectral ratio method of near-surface structures using the power spectrum of strong motion records in the Strong Motion Array in Taiwan Phase I (SMART1). The dense SMART1 recorded significant strong motions in the 1980s, which can be used to identify soil nonlinearity at near surfaces. A 40%–50% increase in frequency-dependent damping for SMART1 was identified, with strain increasing from 0.01% to 0.1% in near-surface regions. A large damping was also found in the shallow sediments with mean Vs below 600 m/s on the topmost 500 m layers in the SMART1 database at a frequency range of 3–8 Hz, which is independent of the magnitude scaling or near-field travel distance scaling relations.