Numerical ground motion prediction for earthquake early warning incorporating correction of rupture directivity effects

Abstract

The essence of earthquake early warning lies in the rapid and reliable prediction of the ground motion field after an earthquake occurs. While current numerical ground motion prediction methods based on data assimilation avoid the challenge of estimating source parameters, their interpolation processes do not adequately consider the source rupture directivity effects—a key physical factor controlling the spatially heterogeneous pattern of ground motions, resulting in limited prediction accuracy. To address this limitation, we break the traditional framework of numerical ground motion prediction methods and propose a novel real-time method that couples the source and ground motion field. This method incorporates a line-source model, dynamically extracts rupture directivity information, and estimates the line-source strike by comparing observed and predicted ground motion fields in real time, thereby continuously refining subsequent ground motion predictions. Tests using the 2016 Kumamoto earthquake (Mw 7.0) as an example demonstrate that the rupture direction inferred by this method within the early post-event period (within 28s) aligns closely with the results from detailed post-event inversion. After correction for the directivity effects, the accuracy of ground motion prediction is superior to that of traditional numerical prediction methods. The MAE of peak intensity predictions is reduced by 16.1%, 5.4%, and 19.6% for predictions of 5s, 10s, and 20s in advance, respectively.