扩展的横向变速叠前时间偏移技术

常规叠前时间偏移仅适用于横向缓变速介质，对于横向变速剧烈的介质，其旅行时计算存在较大误差，远偏移距误差更大。针对这一问题，对常规叠前时间偏移双曲线旅行时计算公式进行了改进，提出了扩展的横向变速叠前时间偏移旅行时计算公式。其基本原理是，引入速度函数和加权函数，将偏移距离散化，在每一个偏移距范围内通过加权函数调整均方根速度，由此来修正由横向速度变化引起的旅行时变化，使旅行时的计算精度得以提高，从而加强了时间偏移对速度横向变化的适应能力，改善了偏移成像质量。标准的Marmousi理论模型数据和实际资料的测试结果表明，扩展的横向变速叠前时间偏移能够提高复杂构造的成像精度。

Extended pre-stack time migration for laterally variable velocity

Conventional pre-stack time migration is only suitable to the medium with slow laterally variable velocity. For the medium with acute laterally variable velocity, the computation of its travel time exist large error, especially in far offset. Aiming at the problem, we improved the hyperbolic curve travel time formula for conventional pre-stack time migration, and proposed extended travel time computation formula for pre-stack time migration with laterally variable velocity. The basic principles are as follows: introducing velocity function and weighted function, discretizing offset, and adjusting RMS velocity in every offset range by using weighted function, to modify the travel time changes caused by lateral variation of velocity and improve the computation accuracy of travel time. The method strengthens the adaptiveness of time migration on laterally variable velocity and improves the computation accuracy of travel time. Testing on standard Marmousi theoretical model and actual data shows that the extended pre-stack time migration for laterally variable velocity can improve the imaging accuracy of complex structure.