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海底广角地震剖面反演方法对比——以南海礼乐滩OBS剖面为例

DOI: 10.6038/cjg20140828, PP. 2701-2712

Keywords: 精细地壳结构,时深转换,1D速度,海底地震仪,礼乐滩

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Abstract:

广角地震测线(OBS973-2)位于南海南部陆缘,其地壳深部构造是研究南海共轭扩张及形成演化的直接证据之一.本文采用2D射线追踪技术,结合与之重合的多道地震测线(NH973-2)时深转换结果,对OBS973-2测线重新进行了正、反演研究,得到了礼乐滩及邻近海区的精细地壳结构.与前人结果相比,本文基于正反演速度模型,把测线分为陆壳区(0~200km)、洋陆过渡区(200~280km)和洋盆区(280~370km).地壳结构在不同区域差异明显,陆壳区沉积层厚度横向差异大,且速度横向不均匀,地壳整体厚度大(约20km),有横向速度差;洋陆过渡区速度和厚度横向均匀,地壳减薄(约8km);洋壳区地壳厚度减薄至6km.与以往研究相比,新的认识集中在两个方面,(1)在方法上,综合广角地震和多道地震数据,借助正演和反演方法,能够得到更多更可靠的地壳结构信息.(2)在地壳结构上,结合广角地震与多道地震,得到洋陆过渡区莫霍面向海减薄的形态及其埋深(约12~18km,海平面为0km);进一步验证礼乐滩区域在洋陆过渡区没有明显的高速层,为非火山型陆缘,其共轭扩张点为中沙地块;陆壳区上地壳强烈的拉张作用在速度模型表现出横向速度异常和低速区,在多道地震剖面上表现为大量10~20km的正断层.

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