波动方程有限差分正演，吸收边界，三层均匀介质-Wave equation finite difference attributions,absorbing boundary, three-layer uneven medium

实现了声波波动方程有限差分正演模拟，交错网格下，时间2阶空间10阶-Achieve the acoustic wave equation finite difference forward modeling, staggered under the grid, the time second-order space 10 order