【摘要】 低速带具有"自由表面、低速度、高吸收"的特征,能引起反射波能量减弱,产生很强的频散,造成近地表波场畸变,严重影响地震勘探的精度。而地震采集过程又不可避免遇到以下低速带问题:1低速带存在与否会对地震波传播造成什么影响;2近地表变化大,怎么才能得到精确的低速带参数;3存在低速带时,激发井深、最佳的药量(与子波频率有关)、最佳的耦合(与低速带速度相关)等采集参数会对采集资料的品质产生什么影响。本文通过数值模拟,集中对低速带与地震波激发的井深、速度、子波主频等核心采集参数的关系进行分析研究,同时在低速带背景下对数值模拟的网格、边界等问题也进行了讨论。模拟得到的波场特征及低速带参数影响的机理分析,对做好野外地震波激发,获取高品质的地震资料,具有理论意义和指导作用。更多还原

【Abstract】 The complexity of near surface and geological underground structure can intensify the diversity of seismic wave field, affect the quality of seismic records strongly, especially the existence of low velocity zone(LVZ) has great effect on seismic wave field. Low velocity zone characteristic of the "free surface, low velocity and high absorption" can cause the reduction of reflection wave energy, strong dispersion and distortion of surface wave field, which affects the accuracy of seismic exploration. However the seismic acquisition will face the following problems of low velocity zone inevitably:(1) what effect will be caused by the low velocity zone to seismic wave propagation;(2) Near-surface change is big, so how to get the accurate parameters of low velocity zone;(3) when there exists the low velocity zone, what effect will seismic acquisition parameters of the shooting depth, the best dosage(related to wavelet frequency) and the best coupling(related to LVZ velocity) bring to the seismic data quality. This paper analyzes the relation of low velocity zone with shooting depth, speed, wavelet frequency(dose effect), etc. based on the seismic numerical simulation method. At the same time, this paper discusses the grid and the absorbing boundary of the seismic numerical simulation under the background of low velocity zone. The wave field characteristics and low-velocity layer parameters influencing mechanism analysis will have theoretical significance and guiding effect to the field seismic wave shooting and to get high quality seismic data.更多还原