论文部分内容阅读
传统的走时地震层析方法都是建立在射线理论的基础上，而实际地震信号的能量是来自一个连接激发点和接收点的菲涅耳体，并非单纯地来自于一条假想的射线。本文的目的是把菲涅耳体的概念引入到层析成像中去，其优点是；①菲涅耳体层析成像会保持数据本身的分辨率；②增强射线覆盖量；③抗误差（在层析正演过程中由于初始速度场的不准确性造成的射线误差）能力强。理论模型测试证实了菲涅耳体层析成像的这些优点。在理论模型的制作中，我们发现了从理论记录上拾取的走时和直接计算的走时存在着差异：当射线穿过高速异常时，理论模型的走时往往小于计算的走时；反之，当射线穿过低速异常时，理论记录的走时又大于直接计算的走时。对于任何一种以射线走时为基础的层析方法，都将会受到这种走时异常的影响。
The traditional time-history seismic tomography method is based on the ray theory. However, the actual seismic signal energy comes from a Fresnel body connecting the excitation point and the receiving point, not simply from an imaginary ray. The purpose of this paper is to introduce the concept of Fresnel body into tomography. The advantages are: (1) Fresnel body tomography will maintain the resolution of the data itself; (2) enhance the coverage of radiation; (3) Ray error due to inaccuracy of initial velocity field during tomographic forward). Theoretical model testing confirms these advantages of Fresnel tomography. In the production of the theoretical model, we find that there is a difference between the travel time and the direct travel time picked up from the theoretical record: when the ray passes through the high-speed anomaly, the travel time of the theoretical model is often smaller than the travel time of the calculation; on the contrary, At low speed anomaly, the theoretical record of travel time is greater than the direct calculation of travel time. For any kind of tomography based on the ray travel time, it will be affected by this travel time anomaly.