[S-SS09] Strong Ground Motion and Earthquake Disaster

[SSS09-14] Application of the real-time seismic wave field on the earthquake early warning system

*Da-Yi Chen¹ (1.Seismological Center, Central Weather Bureau of Taiwan)

Keywords:Earthquake Early Warning, Wave Field, Real-time seismic intensity

The earthquake early warning system (EEWS) is working based on the real-time seismic data. After the procedure of the data processing and the estimating related source parameters, the EEWS is able to send warnings to the alerted areas. In order to timely issue warnings, limited number of triggered stations were used in the initial stage of the EEWS. However, the uncertainties of the estimations would be large. Generally, the EEWS can be considered as two modes, such as point source mode, and the wave field mode. In the point source mode, the information of the P wave is used to estimate the origin time, epicenter, depth and magnitude. Consequently, the predicted seismic intensities are made by using the ground motion prediction equations. In the wave filed mode, the real-time observed seismic intensities could construct a wave field that can be used to predict the seismic intensities in the next second. The challenge of the EEWS comes from a mega earthquake (typically with a magnitude of 7 or larger) and its intense aftershocks. The magnitude of the main shock might be underestimated because of lack of considering the effect of the finite fault, site effect, and the directivity. The warnings could be lost for the large aftershocks because the P waves might be difficult to be recognized. The false alarm might be happened when two small earthquakes occurred within a short time interval. Because the procedure of the association could be wrong, P-wave arrivals from the two earthquakes might be considered coming from the same event. As a result, the EEWS overestimate the magnitude and the predicted intensities as well. The purpose of this study is to use the wave field concept to overcome the previous problems and try to reduce the processing time. Figure 1 shows the station distribution of the real-time seismic network used in the current EEWS operating in the Central Weather Bureau of Taiwan. Over 500 strong motion seismometers were used in this study for the calculations of the real-time seismic intensities. The 2022 magnitude 6.8 Taitung earthquake and its aftershocks were simulated and tested. The results show that the wave field approach is able to preventing from underestimating seismic intensities of the main shock and issuing false alarms when multiple events occurred in a short time.