The distribution of damage due to recent earthquakes has shown that the effects of shallow geological structures on the level of ground shaking represent an important factor in engineering seismology. Whereas many previous studies have estimated site amplification factors in the frequency domain, their application to the real‐time modeling of ground motion is not yet fully established. In this article, a method for the real‐time correction of frequency‐dependent site‐response factors is proposed, which accounts not only for the modulus, but also for the changes in the signal phase related to local site conditions. The transformation of the complex standard spectral ratios to a causal recursive filter in the time domain allows for the forecasting of the waveforms for soft‐soil sites almost in real time when the signal is recorded earlier at a reference site. When considering travel‐time differences of the various seismic phases between the hypocenter and the studied sites, the level of ground motion at soft‐soil sites with respect to arrival time, energy, duration, and frequency content can be well constrained, even in cases of a high spatial variability of the amplification patterns.