摘要
低降速带对地震波的强烈吸收作用影响地震勘探的分辨率,地表的剧烈起伏造成了我国西部地震勘探中信噪比低的问题。针对这2个问题,提出了地质模型中地震波传播数值模拟的方法,并对模拟结果进行了分析。在考虑纵横波Q值的基础上,利用交错网格高阶差分法对粘弹性介质中地震波传播进行了数值模拟。利用纵向坐标变换将起伏地表转换为新坐标系下的水平地表,进而利用交错网格高阶差分方法对起伏地表情况下的弹性波传播进行了数值模拟。这种模拟方法的主要优点是自由边界条件实现比较方便,数值频散小,模拟精度高。通过模拟实例发现,地表低降速带使地震波频带变窄,频率降低,影响了深部地层的地震勘探分辨率,模拟结果可以用来进行提高分辨率的地震处理方法研究。地表起伏使地震波在近地表的传播变得异常复杂,引起面波、体波等地震波型之间的相互转化,产生了大量的地表散射,从而引起了山地地震勘探中严重的低信噪比问题。通过弹性波模拟可以对各种地表干扰加以识别,以指导实际地震资料的去噪处理。
The strong absorption of seismic wave by low velocity layer affects the resolution of seismic exploration. Low signal-to-noise ratio (S/N) arises from sharply wavy terrain in western China. To cope with these two problems, this paper studied methods for numerical simulation of seismic waves in geologic model,and analyzed the results of numerical simulation.Taking the Q-values of P- and S-wave into account, numerical simulation of seismic waves in viscoelastic media was implemented by staggered higher-order difference scheme. Wavy terrain was firstly changed into horizontal terrain with vertical coordinate transformation, and then numerical simulation was carried out. This method has advantages of small numerical dispersion, high simulation precision, and easy imposition of free boundary conditions. Examples of numerical simulation show that low velocity layer leads to narrowing of seismic wave frequency band,as well as decrease of frequency and resolution of deep formations. This result is helpful for the study of high resolution seismic data processing methods. Wavy terrain complicates the propagation of seismic waves in near surface. It leads to conversion of different waves such as surface wave and body wave as well as generation of scattering at surface, thus severely deteriorates the S/N of seismic exploration in mountainous areas. Simulation of elastic waves facilitates the recognition and elimination of different surface interferences.
出处
《勘探地球物理进展》
2005年第3期187-194,共8页
Progress in Exploration Geophysics
关键词
低降速带
起伏地表
数值模拟
交错网格
高阶差分
分辨率
信噪比
low velocity layer
ragged surface
numerical simulation
staggered mesh
higher order difference
resolution
signalto-noise ratio
