( 2 ) calculating the gridded rayleigh wave attenuation factor y and group velocity . the lsqr algorithm is used to inverse the attenuation factor and group velocity under 4 ? x4 ? gridding and 2 ( 2 )进行rayleigh波衰减系数、群速度网格化纯路径衰减反演计算,得到网格单元纯路径衰减系数和群速度分布结构。