| 摘要: | 西元1906年M 7.1梅山地震為台灣史上一重大災害性地震，其造成數千的人員傷亡及房屋毀損。由於缺乏地震觀測，近100年來對於此地震的相關研究與調查相當稀少。本研究的主要目的是重新審視此地震震源並評估1906年梅山地震的動力學參數。透過根據摩擦極限、斷層幾何、流體壓力、岩石強度、流變、靜摩擦係數和應力降等物理和數學約束之應力與摩擦行為條件約束過程，本研究建立了192個實驗模型。在線性滑移弱化模型和均質半空間中，以3D有限元素法進行運算。透過對破裂模型的比較，討論歷史地震之動力學參數的可能範圍。選擇最合理的破裂模型後，結合1906年梅山地震的餘震分佈，比較模擬與觀測波形的P波初動與振幅和震度圖。當靜摩擦係數在0.4至0.5間時，斷層的成功破裂暗指此研究區域不適用拜耳萊定律。模型的平均應力降而在數十至數百個巴，其數值與台灣相同規模的地震應力降相似。液體超壓會使得岩石強度變弱，造成破裂面積與滑移之增加。根據破裂過程、波形和震度圖之比較，以多段模型擬合之結果最佳。本研究從動力學角度來看，破裂不是單獨發生在梅山斷層上，而是由逆衝構造觸發梅山斷層的破裂。此研究的分析結果，呈現梅山地震與尚未被廣泛考慮的逆衝構造之關聯性，更符合台灣西部的其他重大事件，如1999年的集集地震。;The March 17, 1906 (UTC) M 7.1 Meishan earthquake is one of the most devastating events in Taiwan’s history. The investigation in the past 100 years on this large event is rather limited due to the lack of seismic observation. However, with the advent of numerical simulations, dynamic rupture modeling provides an additional technique to understand source properties and the rupture process of the Meishan earthquake.
In this study, the primary target is to revisit the source and assess the dynamic parameters for the 1906 Meishan earthquake. Based on physical and mathematical constraints from frictional limit, fault geometries, fluid pressure, rock strength, empirical flow law, static friction coefficient, and stress drop, I build up 192 models for the experiment. The models are run in the linear slip-weakening model and on a 3D finite element mesh in a homogeneous half-space. By comparison of the resulting rupture conditions from the suite of ruptured models, I discuss the possible ranges of dynamic parameters for the historical earthquake. Following the selection of the most reasonable models, I compare the polarities and amplitudes of the synthetic waveforms to the waveforms observed on Omori seismographs in addition to the intensity maps in conjunction with the distribution of the aftershocks of the 1906 Meishan earthquake.
Resulting rupture processes show that the static friction coefficient ranges from 0.4 to 0.5, implying that Byerlee’s law does not hold for the region. Average stress drops in our models are in the range of few to few tens of MPa, and is in range of stress drops of similarly sized earthquakes in Taiwan. Fluid overpressurization weakens the rock matrices, and therefore, during rupture expands area and increases slip. According to the rupture process, waveform comparison, and seismic intensity simulation, the results provide considerably well-fit polarities and amplitudes from waveforms and similar intensity patterns with historical intensity maps for multiple-segment models. This study indicates that rupture occurred on multiple faults connected to the Meishan fault rather than on the Meishan fault alone. The results in this study suggest that the Meishan earthquake with its thrust fault association is closer in its faulting characteristics to other major events in western Taiwan, such as the 1999 Chi-Chi earthquake, due to this not yet widely considered thrust component. |
