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Please use this identifier to cite or link to this item: http://ntour.ntou.edu.tw:8080/ir/handle/987654321/24731

Title: Deep Seismic Imaging of Crustal Structures in the Northern South China Sea and the Western Philippine Sea Between TAICRUST and TAIGER
Authors: Wang T.;Lee C.;Yang B.;Deng J.;Chen T.
Contributors: NTOU:Institute of Applied Geosciences
國立臺灣海洋大學:應用地球科學研究所
Keywords: 0910 Data processing;0930 Oceanic structures;0935 Seismic methods (3025, 7294);7220 Oceanic crust;8105 Continental margins: divergent (1212, 8124)
Date: 2008
Issue Date: 2011-10-20T08:17:31Z
Publisher: American Geophysical Union
Abstract: abstract:Several deep seismic surveys, by using portable ocean-bottom seismometers (MicrOBS) and small air-gun shots, in the northern South China Sea (SCS) and the western Philippine Sea were conducted after 1995 TAICRUST experiment. In 2007, 30 MicrOBS data along three NW-SE lines were acquired in the continental slope of the northern SCS. The results show that west of 117 E along the continental slope, transitional crust consisted of mainly the extended and thinned continental crust was imaged. However, east of 117 E, both extended continent northwest of the continent-oceanic boundary (COB) and thick (13 km) oceanic crust between the COB and the Manila Trench were found. We observed that thickness of the igneous body (7-7.5 km/s) in the thick oceanic crust is from about 1 km at COB southeastward increasing to 7 km below the Manila Trench. Therefore, the transitional crust along the continental slope of the northern SCS may have not resulted only from volcanism or magmatism of post seafloor spreading in the South China Sea but also due to subduction of Eurasian Plate beneath the Philippine Sea Plate. Tectonic setting of the transitional crust with subduction and volcanism appeared in the northern SCS is similar to those in the Central Asian orogenic belt and the Moroccan Atlantic Margin. In 2006, 24 MicrOBS stations along one E-W and two S-N lines were retrieved in the western Philippine Sea. OBS imaging indicated that the crustal thickness of the Huatung Basin decreases northward from 10-11 km to 7 km whereas the crustal thickness of the western Philippine Basin increases northward from 7 km to 9 km. The thick oceanic crust in both regions is associated with a high P-wave velocity of 6.6-7.5 km/s and a low Poisson's ratio of 0.28 imaged in the middle and lower crust. However, the difference of the crustal thickness resulted from the formation of Gagua Ridge between the Huatung Basin and the western Philippine Basin. We found that three old fracture zones, one below the summit of the Gagua Ridge and the others beneath two edges of the Gagua Ridge, are observed from a large lateral variation of P-wave velocity of about 5.5-6.4 km/s and a low Poisson's ratio of 0.29 in the upper crust. Therefore, Gagua Ridge had been generated by compression, shearing and uplifting (or transpression) due to the eastward convergence of the Eurasia Plate and the northwestward convergence of the Philippine Sea Plate. 2009 TAIGER experiment, by providing strong air-guns and more OBS deployment, will enable us to enhance the imaging of the lower crustal and the upper mantle covering from the northern SCS, Manila subduction zone and the western Philippine Sea.
Relation: 89期,P T33E-01
URI: http://ntour.ntou.edu.tw/handle/987654321/24731
Appears in Collections:[Institute of Applied Geosciences] Lecture & Seminar

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