基于波场延拓的沉积层反演与基岩接收函数的岩石圈成像，及其在华北地区的应用

In China many important tectonic structures are covered by sedimentary basins. The complex seismic waves propagations inside the shallow low-velocity sedimentary layer deteriorate the quality of seismic records and also images of deep structures. To solve this problem, we first estimate the sedimentary structure from seismic records and then downward continue the wavefield from recording surface to bedrock depth underneath the sedimentary layer. This process eliminates the sediment reverberations from the data so that the images of deep structures can be improved. Under processes such as continent-continent collision and subduction around or beneath it, North China Craton has lost most of its mantle root and forms broadly distributed sedimentary basins since Mesozoic, which is an important area for the study of seismic structures and tectonics. We invert for its sedimentary and crustal structures to better understand and differentiate the regional tectonic mechanisms, meanwhile, the seismic structure of the basin provide important information for strong ground motion predictions and oil/gas distributions in North China.

我国有很多重要的构造块体为沉积盆地覆盖。在地球物理探测中，由于地震波在地表低速沉积层中复杂的传播效应，导致数据质量的降低，进而影响深部结构的成像和识别。为解决该问题，我们首先从地震记录中估计出沉积层的速度结构，然后将地表波场记录延拓至沉积层下方的基岩地壳处，从而去除沉积层多次波的影响，提高深部结构成像的可靠性和精度。在陆陆碰撞和板片俯冲等构造作用的影响下，我国华北克拉通自中生代以来发生大规模的岩石圈减薄，形成大量的沉积盆地，是地震学和大地构造研究的重点。我们通过对华北地区沉积层及地壳结构的研究，不仅有利于理解和区分该地区的构造演化机制，也为沉积盆地强地面运动估计以及油气分布探查提供了重要的资料。

反演盆地的沉积层速度结构对于探索地下自然资源、评估地震灾害有着重要意义。由于数据采集的高成本，盆地内的2-D/3-D地震勘测的空间覆盖通常非常有限，而近期发展的大规模密集被动源地震台阵提供了一种较经济的具有中等空间分辨率的三维盆地沉积模型反演的手段。我们利用瑞利波相速度、瑞利波垂向-横向振幅比以及远震体波波形，通过贝叶斯联合反演方法获得沉积层速度模型，并通过合成数据测试，验证了方法对不同的沉积层结构反演的有效性。我们进一步将联合反演应用于松辽盆地内的地震台站记录，显示了盆地南北部之间沉积结构的巨大差异，同时反演得到的速度模型能够有效地从台站记录的远震数据中去除沉积层多次波，提升了接收函数的应用效果。