“…For practical applications, the computational efficiency is an important aspect. It is natural to couple the LSM concept and the ray-based wavefield extrapolator, the Gaussian beam propagator (e.g., Hill, 1990Hill, , 2001Hale, 1992aHale, , 1992bAlkhalifah, 1995;Gray, 2005;Gray and Bleistein, 2009;Popov et al, 2010;Yue et al, 2012;Zheng et al, 2013) to obtain faster turn-around time, while retaining the benefit of LSM.…”