A profile study of OBS deep geological detect in the East China Sea
A profile study of OBS deep geological detect in the East China Sea
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DOI：
10.1360/tb-2020-0923
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发表时间：
2021-01-01
影响因子：
1.1
通讯作者：
Pang, Yumao
中科院分区：
文献类型：
--
作者：
Wu, Zhiqiang;Zhang, Xunhua;Pang, Yumao
海底地震仪（OBS）的使用对研究东海的构造演化具有重要意义。为研究东海陆架盆地至琉球海沟隆起褶皱带的深部地质构造特征，在东海海域开展了北西-南东向主动震源深地震实验（OBS-2015）。利用多层炮阵延迟震源，在大陆架和冲绳海槽可获得莫霍面以下的广角地震反射和折射信号，并可识别Ps、Pg和PmP等多种震相。东海OBS深部地学地震勘探的数据采集结果表明，利用中小容量气枪组成的三维阵列震源，也可以获得直至莫霍面的有效地震震相，为OBS深部勘探激发源的选择提供了一条新途径。在对数据进行预处理、震相识别和拾取后，通过射线追踪和旅行时正反演模拟，得到了二维速度结构剖面。地质解释和综合研究表明，东海陆架盆地是一个中新生代沉积盆地，中新生代最大叠合厚度达13 km。东海陆架区地壳是陆壳向海的延伸。莫霍面起伏较小，埋深约30 km。从钓鱼岛褶皱到琉球岛弧，莫霍面起伏剧烈，自西向东快速上升。冲绳海槽区地壳厚度仅为东海陆架盆地地壳厚度的一半左右。它是一个高速地质体，最薄的中心轴约为13公里，两侧迅速增厚（约19公里）。在冲绳海槽地区莫霍面上发育有高速（7.1km/s）异常体。东部凹陷莫霍面明显抬升。这表明与伸展盆地存在明显的镜像关系。冲绳海槽的垂直速度结构与大陆地壳的速度结构有很大不同，而与大洋地壳的速度结构接近。推测莫霍面上发育的厚层高速体是弧后拉张过程中幔源物质大量上涌的表现。结合浅部低速异常岩浆房和岩浆岩穿入沉积基底层的现象，认为测线沿着冲绳海槽南部地壳已破裂并进入海底扩张的初始阶段，冲绳海槽南部已出现初始洋壳，具有非典型洋壳特征。该实验为研究东海地壳深部结构和区域地质演化提供了重要的基础资料。
The use of ocean bottom seismometer (OBS) is of great significance to explore the tectonic evolution of the East China Sea. To study the characteristics of the deep geological structure from the East China Sea shelf basin to the Ryukyu trench uplifting fold belt, the NW-SE active source deep seismic experiment (OBS-2015) was carried out in the East China Sea. By using the delayed fire source of multilayer gun array, wide-angle seismic reflection and refraction signals up to the Moho can be obtained in the continental shelf and Okinawa Trough, and various seismic phases such as Ps, Pg and PmP can be recognized. The data acquisition results of OBS deep geoscience seismic exploration in the East China Sea show that the effective seismic phase up to Moho surface can also be obtained by using the three-dimensional array source composed of medium and small capacity air guns, which provides a new way for the selection of excitation source for OBS deep exploration. After data preprocessing, identifying and picking up seismic phases, a 2D velocity structure profile was obtained by ray tracing and travel time forward and inversion modeling. Geological interpretation and comprehensive study show that the East China Sea shelf basin is a Mesozoic-Cenozoic sedimentary basin with the maximum superimposed Mesozoic-Cenozoic thickness of 13 km. The crust of the East China Sea shelf area is the extension of the continental crust to the sea. The Moho surface has small fluctuation and the buried depth is about 30 km. From the Diaoyu Island fold to the Ryukyu Island Arc, the Moho Surface fluctuates sharply, rising rapidly from west to East. The crustal thickness of the Okinawa Trough area is only about half the thickness of in the East China Sea shelf basin. It is a high velocity geological body with the thinnest central axis of approximately 13 km and rapid thickening to both sides (approximately 19 km). The high velocity (up to 7.1 km/s) abnormal body develops above the Moho surface in the Okinawa Trough area. The Moho surface in the eastern depression has uplifted significantly. This shows an obvious mirror image relationship with the extensional basin. The vertical velocity structure of the Okinawa Trough is quite different from that of the continental crust and is close to that of the oceanic crust. It is speculated that the thick high-speed body developed on the Moho surface is the manifestation of a large amount of upwelling of mantle derived materials during the back arc stretching process. Combined with the phenomena of low-speed abnormal magma chamber in the shallow part and the penetration of magmatic rocks into the sedimentary basement layer, it is believed that the crust in the southern Okinawa Trough along the survey line has ruptured and entered the initial stage of sea-floor spreading, and the initial oceanic crust has appeared in the southern Okinawa Trough and the crust has atypical oceanic crust characteristics. This experiment provides important basic data for studying the deep crustal structure and regional geological evolution of the East China Sea.