A new characteristic parameter max or peak displacement Pd. The comparison results show that for magnitude between 4.0-7.3, Sdτ has better correlation with magnitude and higher estimate accuracy than either τpmax or Pd. Hypocentral distance is not required when using Sdτ, but it can be used to further improve the accuracy of magnitude estimate. These results confirm that Sdτ can significantly improve the accuracy and timeliness of continuous magnitude estimation in an EEW system.