On‐site earthquake early warning (EEW) requires the best estimates of earthquake magnitude and distance parameters within a few seconds after the P‐wave arrival for estimating the subsequent S‐wave parameters. The errors in the estimates of the earthquake P‐wave parameters will propagate into the estimates of the S‐wave parameters. To solve this problem, we used the methodology by Zhao and Zhao (2019), which uses the spectral ratio R3P between the response spectral values of the first 3 s of the S wave and that of the first 3 s of the P wave, referred to as the R3P model. The modeling presented here was based on strong‐motion records from the Next Generation Attenuation (NGA)‐West2 dataset. We also used the spectral ratio RFP between the response spectral values from the full records from the S‐wave arrival time to the end of the record and that of the first 3 s P wave to develop a second EEW model (the RFP model). An advantage of these two models is that the magnitude and hypocentral distance are not required in considerable magnitude and distance ranges. This means that the errors in the estimated source and path parameters from the first 3 s of the P wave will not affect the model predictions. A theoretical justification for these results is that the magnitude and the distance scaling rates for the first 3 s of the P wave are similar to those of the first 3 s of the S wave. This may also apply to the full S‐wave window within useful EEW magnitude and distance ranges. We also found that when the estimated magnitude and distance for a record are necessary, the effect of the corresponding errors would be smaller than using a ground‐motion prediction equation (GMPE), because the magnitude and distance scaling rates from this study are smaller than those of many GMPEs.

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