強主震的發生經常會破壞結構，造成財物損失或人員傷亡，之後發生的大規模餘震，可能進一弱化結構，加劇損失與傷亡，甚至危害救災的進行，因此強主震的風險評估及強主震發生後即時評估最大規模餘震的風險是重要的研究議題。本文首先根據台灣氣象局的完整地震目錄，藉分群分析選取1978-2022期間發生在台灣地區的規模5.0以上之主震，探討其規模分配，以及接連發生的主震間隔時間之分配。針對上述主震對應的最大規模餘震，探討最大餘震與主震的規模差距與時間差距之聯合分配。本文進一步分析不同的主震震源機制對於上述主震規模、主震間隔時間及最大餘震相關分配之影響。本文發現台灣主震的規模分配及最大餘震與其主震規模差距之分配與主震震源機制相關。

The occurrence of a strong mainshock often results in the destruction of structures, leading to property damage and casualties. The subsequent large magnitude aftershocks may further weaken the structure, increase losses and casualties, and even endanger disaster relief. The evaluation of the risk of mainshocks and the forth coming largest aftershocks is hence an important research topic. The mainshocks with a magnitude of 5.0 or more that occurred in Taiwan during 1978-2022 are selected from the complete earthquake catalog of the Central Weather Bureau by using a cluster analysis. The distribution of the mainshocks magnitude and the distribution of the interoccurrence time of successive mainshocks are then discussed. Moreover, the largest aftershock corresponding to the mainshocks are selected. The joint distribution of the magnitude difference and time difference between the largest aftershock and the mainshock is then investigated. The effect of different mainshock focal mechanisms on the above distributions is further analysed. The study finds that the distribution of the mainshock magnitude and magnitude difference between the largest aftershock and mainshock in Taiwan is related to the focal mechanism of the mainshock.

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