初至旅行时层析反演近地表模型精度分析

Analysis on inversion accuracy of near-surface model inversed by first break traveltime tomography

为了提高初至旅行时层析反演近地表速度模型的精度,改善静校正效果,本文研究了激发井深以及约束速度对反演精度的影响。通过建立典型低降速层近地表模型,首先对比分析零井深、井深穿过低速层和井深穿过降速层三种情况下,射线穿过网格的特性及激发井深在低速层以下时,最小约束速度对低速层反演效果的影响;其次利用井口时间确定最小约束速度,并提出了辅助点激发确定最小约束速度的新方法;最后应用于合成与实际地震数据,提高了反演精度。

In order to improve the inversion accuracy of near-surface model inversed by first break traveltime tomography,and then to enhance static corrections more effective,the paper discusses the impact of source depth and constraint velocity on the inversion accuracy.Based on typical synthetic near-surface model,we adopt analysis on the characteristic of ray paths from the source on the surface,the source below weathering and the source below sub-weathering.We discuss the impact of the minimum constraint velocity on the inversion of the weathering when source depth is below weathering.Furthermore,uphole time is involved to determine the minimum constraint velocity and a new method to determine the minimum constraint velocity,called auxiliary source,is also described.Finally the method is applied both to synthetic data and real seismic data and results show that the inversion accuracy is improved.