We numerically simulate seismic wave propagation from the 1999 Mw 7.4 earthquake in Izmit, Turkey, using a 3D finite difference method based on published finite-source models obtained by waveform inversions. This earthquake has been reported, based on observations at the near-fault station SKR, as an example of supershear rupture propagation toward the east. Although the modeled ground motion does show a characteristic Mach wave from the fault plane, it is difficult to identify any particular effects in terms of peak ground velocity (PGV), an important parameter in earthquake engineering. This is because the fault’s spatial heterogeneity is strong enough to mask the properties of supershear rupture, which has been reported through several numerical simulations mostly based on homogeneous fault conditions. This article demonstrates the importance of studying ground motions for known earthquakes through numerical simulations based on finite-fault source models.