Numerous monopile-supported offshore wind turbines (OWTs) have been installed in seismic regions. Meanwhile, scour phenomena caused by ocean wave-current action impact the dynamic characteristics of OWTs, resulting in more challenges. However, such combined effects of scour and earthquake on responses of OWTs with different relative densities in sands are not well understood. In this study, an efficiently integrated numerical model is proposed, considering dynamic soil-structure interaction (SSI) effects. Dynamic SSI phenomena are captured using lumped parameter models (LPMs), which are developed through fitting frequency-dependent impedance functions. Then, scour effects on seismic responses of monopile-supported OWTs in loose and medium-dense sands are investigated. Results indicate that as the scour depth increases (the primary influencing factor at scoured sites), the natural frequency of the offshore wind turbine decreases obviously. Therefore, the seismic responses are significantly changed, and the OWTs in medium-dense sands are more sensitive to scour effects. Certainly, the seismic spectral characteristics also play an important role in the computational outcomes.