地震初至波速度层析成像技术在南黄海盆地崂山隆起的应用

APPLICATION OF SEISMIC FIRST ARRIVAL VELOCITY OF TOMOGRAPHY IMAGING TO LAOSHAN UPLIFT OF THE SOUTH YELLOW SEA BASIN

崂山隆起位于南黄海盆地的中部,新生代地层沉积薄,其底部存在高速屏蔽层,加上中—古生代地层经历了多期构造运动,导致中—古生界地震有效反射信号弱、成像效果较差,地震处理中采用常规速度谱拾取不能准确获得高速屏蔽层下的地层速度,给叠前时间偏移和叠前深度偏移的速度建模工作带来很大困难。近几年,青岛海洋地质研究所在南黄海崂山隆起采集了大容量震源长电缆地震数据,获得了来自中—古生界的初至波信息。采用初至波层析成像方法来揭示高速屏蔽层下中—古生界速度变化信息,主要通过拾取初至波时间,建立初始速度模型,经过不断迭代反演得到最终速度模型。结果表明,高速屏蔽层下地层速度横向变化剧烈,存在速度为3 500～4 000m/s的低速层,预测为碎屑岩;速度为5 100～5 500m/s的高速层,预测为碳酸盐岩地层。

The Laoshan Uplift is located in the middle of the South Yellow Sea Basin.There is large difference of impedance between the Cenozoic and the Mesozoic-Paleozoic.It is,therefore,inferred that there should be a high-speed shield layer at the bottom of the Cenozoic,and the Meso-Paleozoic has experienced complicated tectonic deformation,and resulted in a low signal/noise ratio and poor seismic images.Therefore,it is difficult to acquire the accurate velocity of the Meso-Paleozoic through conventional picking up of stacking velocity in seismic processing,that has brought great difficulties to the velocity modeling of the prestack time migration and prestack depth migration.Qingdao Institute of Marine Geology（QIMG）has collected great amount of seismic data of large-capacity source and long cable from the Laoshan Uplift of the South Yellow Sea Basin,obtained the first-arrival wave from Meso-Paleozoic strata.This paper applies the first arrival wave tomography to inverse the MesoPaleozoic velocity in the high-speed shield layer,mainly through picking up the first arrival-time and building up a velocity model by continuous iterative inversion,finally get the result velocity model.The result shows that velocity changes severely in lateral direction beneath the high-speed shield layer.The low-velocity layer may indicate clastic rocks with a velocity ranging 3 500-4 000m/s,and the high-velocity layer indicate carbonate rocks with a higher velocity within the range of 5 100-5 500m/s.