FFD叠前深度偏移技术在高速铁路断裂勘察中的应用研究

Research on Application of FFD Pre-stack Depth Migration for Fault Exploration on the High-speed Railway Engineering

在国家路网铁路工程的设计与建设中,隐伏断裂勘察一直是线路勘察中的重点,现阶段通常选用浅层地震反射法探测断裂带信息。在浅层地震反射处理过程中,针对常规地震反射偏移方法对地下复杂地层(例如:大倾角地层、断裂带)成像效果不理想问题,引入傅里叶有限差分前深度偏移方法。首先将地下复杂介质速度场分解成背景场和速度扰动场,分别对两部分速度场进行相移处理和时移、高阶校正处理来完成波场延拓,然后将炮点的下行波场与接收点的上行波场采用时间一致性成像条件进行成像。最后借助于商合杭高铁隐伏断裂勘察、济青高铁断裂勘察中的某条浅层地震反射测线进行成像效果测试。结果表明:FFD叠前深度偏移方法能对速度横向变化较剧烈的复杂区域(断裂带)进行准确的成像,改善成像效果。

The survey of hidden fault zone has been a key of the line survey all the time in the design and construction of national railway network project, but the shallow seismic reflection method is usually used to detect fault zone at present. In the process of shallow seismic reflection, in order to solve the problem that the conventional seismic reflection migration method is not ideal for imaging complex underground strata, such as large dip strata and fault, this paper introduces fourier finite difference( FFD) prestack depth migration method, which has an advantage of imaging for complex layer such as steep dip layer. At first, the velocity field of underground complex layer is decomposed into a background field and a velocity disturbance field, and the phase-shift processing, the time-shift processing and high-order correction processing are carried out respectively to complete the wave field continuation. Then the downward wave field of the source point and the upward wave field of the receive point are imaged by using time-consistent imaging conditions. In the end, this paper, the shallow seismic reflection datas of Shanghehang high-speed railway and Jiqing high-speed railway is used to test the imaging effect of this method. the result shows that FFD pre-stack depth migration method can accurately image for complex areas(fault) with drastic lateral velocity variation, and it can improve imaging effect.