台灣位於地震頻繁的板塊交界處，且時常發生中大規模的地震，因 此擁有一個能夠提供準確預警的地震預警系統尤為重要。目前台灣氣象 署使用的地震預警系統屬於區域型地震預警，在區域型地震預警中，強 地動模型（GMM）為不可或缺的一部分。當中大規模的地震發生時，震 源時常產生破裂方向性，造成破裂方向上的地動值有明顯被放大的現象， 若我們使用 GMM 預估地動值的過程中未加以考慮，則破裂前進方向上 的地動值可能會被嚴重低估。本研究將破裂方向性效應加入 GMM 的計 算中，採用線震源考慮破裂方向性的設定，針對台灣近十年 Mw > 5.5 的 15 個地震和集集地震進行地動值預估。在預估過程中，我們實施了近震 源修正，以避免預估值過大或過小的情況，最後將結果與未考慮破裂方 向性的點震源和線震源結果進行比較。由於較大規模的地震可能都伴隨 著破裂方向性效應，因此使用線震源考慮破裂方向性預估的地動值結果 大部分都比未考慮破裂方向性的預估結果更好。另外，本研究測試了逐 秒破裂的地動值預估，以將其應用於地震預警系統中。研究結果顯示， 大部分地震事件的地動值預估在 15 秒至 20 以內即可達到穩定的狀態， 這表明該方法在地震預警系統中具有可行性。綜上所述，本研究不僅能 夠近即時地決定破裂方向，同時也能快速地評估破裂方向上的地動值， 並且有效地提升預估結果的準確性，以更好地改善地震預警的表現。;Taiwan is located on the boundary between the Eurasian Plate and the Philippine Sea Plate and frequently experiences moderate or large-magnitude earthquakes. Therefore, it is critical to have an accurate earthquake early warning system. Currently, the Central Weather Administration in Taiwan employs a regional earthquake early warning system where Ground Motion Models (GMM) are indispensable. During a larger-magnitude earthquake, the directivity effect is caused by source rupturing. Specifically, the propagation of the rupture can lead to significant amplification of ground motion along the direction of the fault rupture. If the rupture directivity is not considered in ground motion models, predicted ground motions in the direction of rupture propagation may be seriously underestimated. This study uses a GMM and a rupture directivity function to predict PGA and PGV. We chose to use a line source considering rupture directivity to estimate ground motion for 15 earthquakes with magnitudes greater than 5.5 in Taiwan over the past decade, as well as the Chi-Chi earthquake. In the estimation process, near-source corrections were implemented to mitigate overestimation or underestimation issues. Next, the results obtained using a line source considering rupture directivity will be compared with those obtained from point and line sources that do not consider rupture directivity. The rupture directivity effect is usually observed during larger magnitude earthquakes, and therefore, the performance of ground motion estimations using a linear source considering rupture directivity is generally better than those that do not consider directivity. Additionally, the study tested real-time ground motion estimation using instantaneous rupture and showed that stable states can be achieved within 15 to 20 seconds for most earthquake events. It indicates the feasibility of this approach in earthquake early warning systems. Thus, the research achieves multiple objectives: real-time determination of rupture direction, rapid assessment of ground motions along the rupture direction, and enhancement of prediction accuracy. These advancements enhance the performance of earthquake early warning systems in Taiwan.
