“…In order to improve the accuracy and stability of a FDM in numerical modeling, many methods have been developed, including difference schemes of variable grid (Wang and Schuster, 1996;Hayashi and Burns, 1999), irregular grid (Opršal and Zahradník, 1999), standard staggered grid (Virieux, 1986;Levander, 1988;Robertsson et al, 1994;Graves, 1996), rotated staggered grid (Gold et al, 1997;Saenger and Bohlen, 2004;Bohlen and Saenger, 2006), variable time step (Tessmer, 2000), and implicit methods (Emerman et al, 1982;Zhang and Zhang, 2007).…”