| 摘要: | 台灣位處歐亞板塊與菲律賓海板塊碰撞的聚合邊界，是全世界快速抬升的造山帶之一，本區域的板塊碰撞形式由兩個隱沒系統所形成，地下構造相當複雜，因此地體構造碰撞模型有很多，從典型的薄皮逆衝到岩石圈碰撞，或是其他模型：浮力抬升等。本研究利用台灣大地動力學國際合作計劃（TAIGER）所獲得的大量資料，嘗試描繪台灣底下的Moho面深度，期能對釐清台灣造山帶之碰撞形式有所幫助。 TAIGER計畫2008年實施陸上炸測，包括：1）北中南三條東西向測線（橫貫台灣本島），以800台TEXAN震測儀收錄，200m間距。2）二條南北向測線（縱貫全島及花東縱谷），以地震儀佈站，6km間距。3）震源點10點，每點炸藥量750~3000kg，埋於80m，深12inch孔徑井底施炸。這次實驗共有6個地震觀測陣列與地震網紀錄的資料：1）TEXAN廣角反射震測，2）南北向地震儀陣列，3）氣象局及中研院地震網，4）TAIGER所布的IRIS RT130地震網，5）台灣海峽短週期海底地震儀，6）大陸福建臨時網。 本研究處理東西向三條、南北向二條剖面，及台海資料，以波線追跡法對初達波及明顯反射波相，進行速度模型模擬，初步研究結果如下：1）西台灣底下為標準層狀構造，地殼厚度30公里，2）山區地殼增厚，可達40公里以上，但窄而深；3）雪山山脈底下與中央山脈底下構造不同；4）幾條界限斷層可深達下部地殼，尤其梨山斷層甚為顯著，5）莫荷面深度的分佈情形，大概呈現北厚南薄，且由西向東漸增，至海岸山脈後快速遞減，變化範圍約在30~40km之間。6）北港高區莫荷面淺於30公里，到福建沿岸增至32公里以上，台海中間未見拱起。 Taiwan is located on the converging boundary of Eurasian and Philippine Sea plates, it is one of the most rapidly uplifting orogeny in the world. In this area, the pattern of the plate collision is occurred between two subducting systems, the geological structure here is quite complicate. So there are many models of the tectonic collision, from the typical thin-skinned thrust to the lithospheric collision, or some other models as uplifting of buoyancy. In this study, we attempt to describe the Moho depth beneath Taiwan by using amount of data from the project of Taiwan Integrated Geodynamic Reseach(TAIGER), and expect for the results can make some improvements to the construction of tectonic collision patterns of Taiwan orgoeny. The land-explosion of TAIGER project was carried out from Feb to March on 2008, and it includes：1) 3 W-E line linear seismic arrays which were consisted of 800 Texans with spacing in 200 meters at northern, middle and southern Taiwan; 2) 2 N-S linear seismic arrays which were consisted of seismometers with spacing in 6 kilometers at middle and eastern Taiwan; 3) 10 explosion sources with the dynamite from 750~3000 kilograms which were set at the depth of 80 meters in the hole with an aperture of 12 inches, and the sources were located on the northern and southern W-E line from the west to the east. We get 6 kinds of data from this experiment, including：1) the wide-angle reflections of Texans; 2) the N-S seismometer arrays; 3) the seismic network of Central Weather Bureau(CWB) and Institute of Earth Science(IES); 4) the seismic array of Reftek 130(RT130) from IRIS in TAIGER project; 5) the short period of Ocean Bottom Seimometer(OBS) array in the Taiwan Strait; 6) the temporary seismic array in mainland China. In this study, we handle the data from 3 W-E transects, 2 N-S transects and Taiwan Strait, and simulate the structure model from the first arrival time and more obvious reflections of these data by Ray-tracing method. The preliminary results are as follows：1) It is a standard layered structure beneath western Taiwan and the thickness of crust is 30 kilometers; 2) The crust thickens and becomes more than 40 kilometers in the mountain area, but it is narrow and deep here; 3) The structure beneath Hsuehshan Range and Central Mountain Range are different; 4) There are some boundary faults as deep as to the lower crust, especially the Li-shan fault; 5) The distribution of the Moho depth is basically thicker in the north, shallower in the south and getting deeper and deeper from the west to the east, but finally getting shallower rapidly in the area of Coast Range; 6) The Moho depth is shallower than 30 kilometers in the Peikang Height and deeper than 32 kilometers at the coast line of Fujian, there is no bulge in Taiwan Strait. |
