A Regional Gravity Map for the Subduction-Collision Zone Near Taiwan

臺灣附近之隱沒—碰撞帶的區域性重力圖

顏宏元(Horng-Yuan Yen) ； 梁文宗(Wen-Tzong Liang) ； 郭本垣(Ban-Yuan Kuo) ； 葉義雄(Yih-Hsiung Yeh) ； 劉家瑄(Char-Shuan Liu) ； Donald Reed ； Neil Lundberg ； 蘇福欽(Fu-Chen Su) ； 鐘火盛(Hou-Sheng Chung)

《Terrestrial, Atmospheric and Oceanic Sciences》 6卷2期 (1995/06) Pp. 233-250

並列摘要

To delineate the tectonic character of the subduction-collision zone in the marine area near Taiwan, we have constructed a regional gravity map by reconciling the shipboard data of 15 cruises that have surveyed the region of 20-26°N and 119-124°E over the past 20 years. Among the 15 cruises, three have known, reliable base-tie information. The absolute level for the other 12's cruises are adjusted in such a way that their crossover errors with respect to the other, three are minimized. The root-mean-square difference of the totally 865 crossovers in the final data set is 6.0mgal, representing an acceptable quality considering the multi-agency nature of the source and the rugged seafloor. The distribution of the ship tracks is uneven, with the better resolution around Taiwan but a progressive undersampling toward the east and northwest. To make a regional map, we interpolate both the marine data and the 640 free-air anomaly measurements on Taiwan and its offshore islands into 5 minute spaced grids using a minimum curvature technique. The SEASAT altimetry derived gravity values are placed on part of the map's boundary as an additional constraint in the minimum curvature calculation. On the map, the free-air anomaly ranges from -250 to 350mgal, primarily reflecting the topography, with the maximum and minimum at the high mountains of Taiwan and the Ryukyu Trench-Taiwan intersection, respectively. The Lutao-Lanyu volcanic arc is manifested as a prominent, continuous high from the southern border of the map, merging northerly with the Coastal Range in eastern Taiwan. The Hengchun Ridge shows a much more subdued gravity anomaly than that of the volcanic arc at a similar elevation. The map also delineates the North Luzon Trough as a forearc basin to the west of the arc, the Nanao Basin at the Ryukyu Trench, and to a less extent the Gagua Ridge at 123°E. To illustrate how the marine gravity data constrain crustal structure, a 2-D gravity analysis is performed with a free-air anomaly profile across the Ryukyu Trench taken from this map.

並列關鍵字

Crossover errors ； Free-air anomaly