瑞雷波数值模拟中的边界条件及模拟实例分析

Boundary conditions and case analysis of numerical modeling of Rayleigh wave

应用2×12阶高精度交错网格有限差分法,建立震源位于地表时瑞雷波数值模拟的自由边界条件;同时,采用PML吸收边界条件以消除模拟时的边界反射。通过对均匀各向同性介质及2层介质模型的计算,验证所采用的自由边界条件和吸收边界条件的有效性及波场模拟的正确性。研究结果表明:模拟结果与解析结果相对误差在5%以内,并指出在同一精度下通过提高差分阶数比减少网格间距所需计算时间少。在2层介质模拟的基础上,对含有软弱夹层的3层介质进行模拟,得到更加接近实际情况的地震记录,频散曲线产生多个模式,并出现"之"字型回折。

A free surface boundary condition for numerical simulation of Rayleigh wave was built by using 2 × 12 order high precision staggered grids finite difference when the source was at the free surface. PML absorbing boundary condition was applied to eliminate boundary reflections. Wave-field modeling of homogeneous isotropic medium and two layer models prove the effectiveness and correctness of using the free surface boundary condition and absorbing boundary condition. The results of model simulating show that relative error between numerical and analytic solutions is within 5%. At the same accurate level, improving difference order has less computation time compared to decreasing grids space. On the base of two-layer model, a seismic record is gotten more practically from modeling the soft interlayer model. The dispersion curve of seismic record has many modes and exhibits the shape of zigzag of reversing phenomena.