Modeling Seismic Intensity Envelopes for Earthquake Early Warning Applications

We constructed an analytical function to model the envelope of the seismic intensity (SI) curves and developed relationships to predict the parameters of the envelope function from the seismic parameters. We collected seismic records over the past two decades from the Japan Meteorological Agency seismic network, Kyoshin net, and Kiban–Kyoshin network. These records were converted into SI curves using a real-time SI intensity filter. Although most of the ground-motion prediction equations (GMPEs) focus on peak ground motions, this study focuses on modeling the full envelope of ground motion, which can improve the real-time evaluation of early earthquake warning (EEW) systems. We evaluated the performance of four different envelope functions in modeling these SI curves and found that the combination of one half- and one full-sigmoid function was the most suitable to capture the distinct characteristics of P and S waves. By correlating the envelope function parameters with seismic parameters, we developed a ground-motion model (GMM) for the envelopes that can predict SI curves of the ongoing earthquake at any given time and distance. The predictability of the peak SI by the GMM was comparable to the GMPE of the SI in the previous studies. This envelope GMM has the potential to enhance the accuracy of real-time ground-motion prediction and earthquake magnitude estimation in EEW systems.