南海北部地壳结构重震联合模拟
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摘要
收集了中德合作调查的SO49-18测线北段地震剖面和水深数据,结合区域的声呐浮标、OBS和双船折射等成果信息,利用重力数据,采用LCT综合反演软件,对南海北部的地壳结构进行重震联合模拟,建立了初始2.5维地球物理模型,并由该模型计算出正演理论空间重力异常曲线。同时,采用匹配滤波技术对实测空间重力异常的不同深度异常进行分离,并与计算空间重力异常曲线进行比较,在物性参数合理的范围内逐层进行模型修饰,使计算与实测空间重力异常曲线相吻合,建立了地壳结构初始深度模型。结果显示,南海北部地壳结构总的特点是:从陆架到陆坡,地壳厚度不断减薄,呈连续阶梯状变化,上地壳厚度较小,下地壳厚度较大;北部洋陆过渡带,莫霍面埋深急剧变浅;西北次海盆地壳厚度(莫霍面埋深)较薄;中沙海台,地壳厚度相对较大。
The northern continental margin of the South China Sea has been affected significantly by the Pacific tectonic domain and Tethys tectonic domain in the Mesozoic,and related to the interaction of the Eurasian plate,the Indian plate and the Pacific plate in Cenozoic. Thus,different kinds of crust have been formed in this region. For the purpose of deciding the property of the crust,it is necessary to well understand its structure. According to the seismic and bathymetric data of the northern segment of SO49-18 surveying line which was obtained from the cooperate investigation of Germany and China,the paper studies its crustal features combining with the information of sonobuoy,OBS and two-boat refraction along this line. We first established an initial 2.5D geophysical model using gravity data and seismic profile based on the LCT joint inversion software. Second,we computed the theoretical free-air gravity anomaly from the assumed model. And then we separated anomalies of different depth by a matched filtering method from total anomalies and computed their corresponding theoretical free-air gravity anomalies which were compared with their observed free-air gravity anomalies. Finally,according to the difference between the theoretical anomalies and the observed anomalies we could modify the model layer by layer using some certain reasonable physical parameters to make the theoretical anomaly curve identical with the observed anomaly curve. The crust structure model couldn't be best until the difference is up to minimum. The simulated result of the profile shows that the crustal thickness of the northern continental margin of the South China Sea is thinning from the continental shelf to the continental slope,the thickness of the upper crust is thinner than the lower crust because of the influence of tensional stress induced by tectonic movements in the early Cenozoic,and the Moho depth decreases sharply from the continental margin to the deep-sea basin; the crustal thickness is thinner in the northwest deep-sea basin,and thicker in the sea plateau of Zhongsha Islands.
The northern continental margin of the South China Sea has been affected significantly by the Pacific tectonic domain and Tethys tectonic domain in the Mesozoic,and related to the interaction of the Eurasian plate,the Indian plate and the Pacific plate in Cenozoic. Thus,different kinds of crust have been formed in this region. For the purpose of deciding the property of the crust,it is necessary to well understand its structure. According to the seismic and bathymetric data of the northern segment of SO49-18 surveying line which was obtained from the cooperate investigation of Germany and China,the paper studies its crustal features combining with the information of sonobuoy,OBS and two-boat refraction along this line. We first established an initial 2.5D geophysical model using gravity data and seismic profile based on the LCT joint inversion software. Second,we computed the theoretical free-air gravity anomaly from the assumed model. And then we separated anomalies of different depth by a matched filtering method from total anomalies and computed their corresponding theoretical free-air gravity anomalies which were compared with their observed free-air gravity anomalies. Finally,according to the difference between the theoretical anomalies and the observed anomalies we could modify the model layer by layer using some certain reasonable physical parameters to make the theoretical anomaly curve identical with the observed anomaly curve. The crust structure model couldn't be best until the difference is up to minimum. The simulated result of the profile shows that the crustal thickness of the northern continental margin of the South China Sea is thinning from the continental shelf to the continental slope,the thickness of the upper crust is thinner than the lower crust because of the influence of tensional stress induced by tectonic movements in the early Cenozoic,and the Moho depth decreases sharply from the continental margin to the deep-sea basin; the crustal thickness is thinner in the northwest deep-sea basin,and thicker in the sea plateau of Zhongsha Islands.
引文
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[8]林珍.南沙海域中建南盆地的磁性基底及地壳结构[J].海洋地质动态,2004,3(20):17-24.
[9]丘学林,周蒂,夏戡原,等.南海西沙海槽地壳结构的海底地震仪探测与研究[J].热带海洋,2000,19(2):9-17.
[10]金庆焕.南海地质与油气资源[M].北京:地质出版社,1989:128-141.
[11]姚伯初,曾维军,陈艺中,等.南海北部陆缘西部的地壳结构[J].海洋学报,1994,16(3):86-93.
[12]姚伯初.南海西北海盆的构造特征及南海新生代的海底扩张[J].热带海洋,1999,18(1):7-15.
[13]SYBERG F J R.A Fourier Method for the Regional-Residual Problemof Potential Fields[J].Geophysical Prospecting,1972,20:47-75.
[14]刘青松,王宝仁.应用多次匹配滤波技术进行垂向位场分离[J].物探化探计算技术,1996,18(4):279-286.
[15]高德章,赵金海,薄玉玲,等.东海重磁地震综合探测剖面研究[J].地球物理学报,2004,47(5):853-861.
[2]施小斌,周蒂,张毅祥,等.南海西沙海槽岩石圈的密度结构与热-流变结构[J].热带海洋学报,2002,21(2):23-31.
[3]于鹏,陈华根,王家林,等.南海北部被动陆缘典型剖面的地质-物理模型及其综合解释[J].长春科技大学学报,2000,30(1):76-79.
[4]姚伯初.南海北部陆缘的地壳结构及构造意义[J].海洋地质与第四纪地质,1998,18(2):1-16.
[5]赵岩,张毅祥,姜绍仁,等.南海北部地球物理特征及地壳结构[J].热带海洋,1996,15(2):37-44.
[6]刘建华.南海中部地震反射波特征及其地质解释[J].海洋学报,2000,22(6):74-80.
[7]孟陆基.地震勘探原理[M].北京:石油大学出版社,2005:217-222.
[8]林珍.南沙海域中建南盆地的磁性基底及地壳结构[J].海洋地质动态,2004,3(20):17-24.
[9]丘学林,周蒂,夏戡原,等.南海西沙海槽地壳结构的海底地震仪探测与研究[J].热带海洋,2000,19(2):9-17.
[10]金庆焕.南海地质与油气资源[M].北京:地质出版社,1989:128-141.
[11]姚伯初,曾维军,陈艺中,等.南海北部陆缘西部的地壳结构[J].海洋学报,1994,16(3):86-93.
[12]姚伯初.南海西北海盆的构造特征及南海新生代的海底扩张[J].热带海洋,1999,18(1):7-15.
[13]SYBERG F J R.A Fourier Method for the Regional-Residual Problemof Potential Fields[J].Geophysical Prospecting,1972,20:47-75.
[14]刘青松,王宝仁.应用多次匹配滤波技术进行垂向位场分离[J].物探化探计算技术,1996,18(4):279-286.
[15]高德章,赵金海,薄玉玲,等.东海重磁地震综合探测剖面研究[J].地球物理学报,2004,47(5):853-861.
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