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頁籤選單縮合
題名 | Geomechanical Appraisal of Seismogenic Faults in Northeast Taiwan=臺灣東北部地震斷層的地質力學評估 |
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作者 | 鄧屬予; 李錫堤; | 書刊名 | 中國地質學會會刊 |
卷期 | 39:2 1996.04[民85.04] |
頁次 | 頁125-142 |
分類號 | 353.4 |
關鍵詞 | 活動斷層; 地殼變形; 地震; 臺灣; Active faults; Crustal deformation; Earthquakes; Taiwan; |
語文 | 英文(English) |
中文摘要 | 位於板塊邊界上的臺灣島,地震的分布型態大致上遵循板塊的架構,尤其是深震。 但淺震並非如此,它的分布鬆散廣闊,反應的是地殼表層的變形,雖然受板塊運動的影響, 但也受岩石圈力學性質的控制。為了深入了解臺灣地區的淺震活動,我們從大地構造和地 殼變形著手,以地質力學的觀點來推斷臺灣東北部活動斷層的可能位置和發震淺能。 臺灣東北部活動斷層的可能位置和發震淺能。 臺灣東北部是琉球島弧和臺灣碰撞山脈的接合點。在臺灣的中南部,呂宋島弧和下伏的菲 律賓海板塊仍在西北仰衝中國大陸,但在臺灣東北部和其東延的琉球島弧,菲律賓海板塊 則已俯衝到中國大陸之下。因此從大地應力的角度而言,臺灣中南部是受到擠壓的碰撞帶, 琉球島弧是受到拉張的隱沒帶。臺灣東北部則是處在西壓東張的轉換帶上。 在臺灣的碰撞帶裡,島弧向西北的推擠造成了地殼的壓縮,並決定了最大應力的方向。相 對而言,地殼的重力是最小的大地應力,並隨著山脈的高度和地殼厚度由山脈中心向兩側 減小。由於軸差應力最大的地方地殼最容易變形斷裂,因此山脈的前緣和後背容易發生逆 斷層。事實上,西部麓山帶的外緣和中央山脈的東坡地殼變形明顯,地震活動頻繁,就顯 現了碰撞帶的應變集中現象。 在琉球的隱沒帶上,海溝的吸引力將上伏的大陸邊緣拉裂,使得原本座落在大陸邊緣的碰 撞山脈崩毀,形成宜蘭平原和沖繩海槽的一線裂谷。此時地殼的重力變成最大的應力,而 南北向的水平應力變成最小。由於山脈中心的重力最大,因此地殼變形集中在山脈中央的 裂谷,產生了一系列近乎東西走向的正斷層,並引發了許多的地震活動。 在碰撞帶和隱沒帶之間的過渡帶上,橫向應力大致與重力相等。地殼變形由水平應力主導, 山脈中的逆斷層常被活化成平移斷層,雖然本區的應變並沒有明顯的集中現象,但幾條大 斷層仍然是主要的活動區。 基於地質力學的分析,我們提供了一張新的臺灣東北部活動斷層圖,並對其中各個斷層的 發震潛能做了初步的評估,結果大致上與觀測資料相吻合,不過也引發了一些爭議的課題, 有待未來進一步的探索。 |
英文摘要 | Although the seismicity of Taiwan is induced by the convergent motion between the Eurasian plate and the Philippine Sea plate, the shallow earthquakes are diffusely distributed and not clearly related to plate interactions. Since shallow earthquakes are attributed to the upper crustal deformation, their occurrences are controlled not only by plate interactions but also by the mechanical behavior of the colliding lithospheres. In order to better understand the origin and distribution of shallow earthquakes, the mechanisms of crustal deformation in northeast Taiwan were investigated and used to surmise potential seismogeinc faults. Northeast Taiwan, situated at the junction of the Taiwan orogen and the Ryukyu Arc, is subjected to the compressional force exerted by the indentation of Luzon Arc and the tensile force by the suction at the Ryukyu Trench. Manipulated by these two forces, the stress regime rapidly changes over from compressional in the Taiwan collision zone to extensional in the Ryukyu subduction zone. In the compressional regime, NW-SE compression overwhelms the gravity and drives crustal contraction. Active thrusting occurs in the frontal and rear sides of the mountain belt where the gravitational force is the least and the deviatoric stress the greatest. In the extensional regime, trench suction induces lithospheric stretching, which resulted in the extensional collapse of the collision orogen. Gravity dictates the maximum stress, while the minimum stress lies horizontal and orthogonal to the trench. The central part of the orogen, where the crustal extension is concentrated, collapsed to a rift valley with intense normal faulting and seismicity. In the transitional regime between the two opposite stress regimes, the horizontal stress is nearly equal to the vertical stress, and the crustal deformation is dominated by distributed shear which shows up as strike-slip faults. |
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