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    請使用永久網址來引用或連結此文件: http://ir.lib.ncu.edu.tw/handle/987654321/5467


    題名: 板塊邊界地震引起之重力位能變化;The earthquake-induced gravitational potential energy change at plate boundaries
    作者: 羅仲良;Chung-Liang Lo
    貢獻者: 地球物理研究所
    關鍵詞: 地震;重力位能變化;造山運動;集集地震;隱沒帶;中洋脊;mid-ocean ridge;earthquake;gravitational potential energy;orogenesis;Chi-Chi earthquake;subduction zone
    日期: 2006-06-26
    上傳時間: 2009-09-22 09:54:37 (UTC+8)
    出版者: 國立中央大學圖書館
    摘要: 由於板塊之間聚合或分離的相對運動在板塊邊界區域特別活躍,因此地震活動度在板塊邊界區域也特別旺盛。地震的發生意味著在地殼或是岩石圈存在同震的永久變形,其中在徑向的位移將造成地球的重力位能改變。本論文利用因地震引起的同震變形所造成的重力位能變化,探討地體構造及大地應力之關聯性。東亞地區存在許多板塊邊界,大致上顯示隱沒帶地區因地殼受側向應力擠壓造成本身重力位能增加;反之,在板塊張裂地區地殼因受側向應力拉張造成本身重力位能減少。若以海溝為軸,我們將隱沒帶區分為隱沒帶前後二區,多數重力位能變化分布在板塊隱沒前的區域以減少為主,這可能肇因於板塊隱沒前的撓曲行為;而在海溝之後板塊隱沒區域,重力位能因板塊之間的耦合作用而增加。台灣位於菲律賓海板塊與歐亞板塊聚合處,活躍的板塊運動促成台灣造山運動以及大量的天然地震,長期累積的地殼變形應可以反應在重力位能的變化上。 利用中央研究院的寬頻地震網(BATS)自1995至2003的地震目錄,計算此間因地震引起的地殼重力位能變化,結果顯示在台灣東部區域,因呂宋島弧隨菲律賓海板塊向北擠壓所造成的地殼重力位能增加,明顯的反應在呂宋島弧以及琉球海溝位置;此外,若將台灣南部外海、西南區域、中央山脈、北部中央山脈到台灣東北區域視為台灣造山序列,從地震釋放的重力位能變化可清楚的呈現造山運動從初期碰撞,劇烈碰撞至後碰撞期的整個完整過程,其分布與我們所認知台灣的造山運動吻合。 整個台灣地區在1995年7月至2003年12月因地震引起的地殼重力位能變化為+1.03E+17焦耳,整體平均功率為-2.07E+10瓦特,約為全球因地震減少的重力位能的百分之一。雖然1999年的921集集主震及車籠埔斷層帶破裂在台灣西部麓山帶,但集集地震序列主要貢獻的地殼重力位能變化卻存在中央山脈地區。因此,集集地震可能扮演著誘發長期累積在中央山脈地殼內的應力的角色。 就全球中洋脊等板塊張裂地區,其地殼重力位能變化伴隨地殼擴張速率不同有所改變。平均而言,中洋脊擴張速率較慢地區,其地殼重力位能減少量較多;反之,中洋脊擴張速率較快地區,其地殼重力位能減少量相對較少。全球中洋脊從1976到2004年,因地震改變的地球重力位能相當於2.1E+19焦耳。 Plate boundaries generate enormous earthquakes. The co-seismic change of gravitational potential energy is caused by a mass redistribution due to the earthquake faulting. Generally, the crustal gravitational potential energy is increasing in compressive areas, while the crustal gravitational potential energy is decreasing in extensional areas. The change of gravitational potential energy distribution shows that most of the subduction zones exhibits compressive stress while the spreading centers/backarc riftings undergo extensional stress. However, there is difference of gravitational potential energy change on both sides of the trench: the crustal gravitational potential energy at fore-trench area shows the energy loss while at the back-trench distributes the energy gain. The decrease of gravitational potential energy may be caused by the outer rise of the subducted slab and; oppositely, the increase of gravitational potential energy was induced by the slab subduction during plate convergence. This phenomenon appears at most of subduction zones in East Asia. The Philippine Sea Plate is converging against the Eurasian Plate with a velocity of 7-8 cm/yr near Taiwan, which has caused the Taiwan orogenesis and induced abundant earthquakes. We have examined the corresponding gravitational potential energy change by using 757 earthquakes from the earthquake catalogue of the Broadband Array in Taiwan for Seismology (BATS) from July 1995 to December 2003. Our results show that the variation of the crustal gravitational potential energy strongly correlates with different stages of the orogenesis. Except for the western Okinawa Trough and the southern Taiwan, most of the colliding regions in Taiwan exhibit a gain of crustal gravitational potential energy. In contrast, the lithospheric gravitational potential energy change in the Taiwan region exhibits a reverse pattern of the crustal gravitational potential energy change. For the whole Taiwan region, the earthquake-induced crustal gravitational potential energy change and the lithospheric gravitational potential energy change during the observation period are +1.03E+17 joules and -1.15E+17 joules, respectively. The average rate of the whole gravitational potential energy change in the Taiwan region is very intense and is equal to -2.07E+10 watts, corresponding to about one per cent of the global GPE loss induced by earthquakes. During the past century, the largest and disaster earthquake, the Chi-Chi earthquake, has occurred. The Chi-Chi earthquake sequence provides most of the gravitational energy gain in the middle central Taiwan, instead of the western foothill where the Chi-Chi main shock locates. It implies that the Chi-Chi main shock may trigger the release of the cumulative strain in the crust of middle Taiwan. Finally, the analysis of the global divergent mid-ocean ridge distribution of gravitational potential energy change shows that the cumulative gravitational potential energy change has strong nonrandom tendency with the ridge spreading rate. The fast spreading ridge shows the relatively low gravitational potential energy change. In total, the gravitational potential energy change caused from the earthquake at global mid-ocean ridge is equal to 2.1E+19 joules from 1976 to 2004.
    顯示於類別:[地球物理研究所] 博碩士論文

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