火山岩地震屏蔽层的转换波叠前时间偏移成像

Converted-wave pre-stack time migration in volcanic area

在反射地震转换波资料处理中,准确求取共转换点一直是一个难题,采用叠前时间偏移技术能避免共转换点道集的抽取,而且能够使转换波归位到真正的反射点上,实现准确成像.本文针对火山岩地震屏蔽层的转换波成像问题,通过对转换波共近似转换点道集进行速度分析,建立了转换波叠前时间偏移的初始速度场,通过速度扫描和纵、横波速度比值扫描确定最佳的偏移速度场和纵、横波速度比值,实现了在火山岩高速层覆盖区域的转换波偏移成像.实际资料的成像结果表明,本文采用的近似转换点计算以及转换波叠前时间偏移方法是有效的.

How to get exact common converted points is a key problem in processing reflection seismic converted wave data. Using pre-stack time migration technology （PSTM）, we can exactly image the converted waves on the true reflection points and avoid sorting common converted point （CCP） gathers. In this paper, we research the imaging problems beneath volcanic area. We sort common asymptotic conversion point （CACP） gathers and perform velocity analysis to establish the initial velocity which will be used in PSTM. By scanning migration velocity and Vp/Vs, we get the optimum migration velocity and Vp/Vs. Using real data from a seismic exploration, we achieved the migration sections of converted wave beneath volcanic area, and it is proved that the method is effective for computing common asymptotic conversion point and pre-stack time migration.