Abstract：The RANSAC-PSO algorithm is used to study the problem of gross errors ingeodetic data as a resultof fault slip parameters inversion. In the simulation experiment, 1%, 5% and 10% of the gross errors are added to the theoretical observations. Particle swarm optimization, selecting weight iteration and RANSAC-PSO algorithm are used to inverse the fault slip parameters. The results show that the difference from the theoretical value is 23.2 cm by the PSO, it is 26.2 cm by the selecting weight iteration, however, it is less than 1cm by RANSAC-PSO, when the gross error rate is 10%.The characteristics of Lushan earthquake are thrust-dominated with a small amount of left-lateral strike-slip.In this paper, the PSO algorithm and RANSAC-PSO algorithm are used to calculate the fault slip parameters,respectively, with the coseismal GPS displacement data. The strike-slip is 00518 m and dip-slip is 0.8289 m by RANSAC-PSO algorithm, which are greater than the results of PSO. In addition, the energy released is 1.000 9×1019 N·m(MW6.63), which is consistent with GCMT 1.060 0×1019 N·m. The horizontal displacements of the ground surface are recalculated with the sliding parameters that invert by the RANSAC-PSO algorithm and the PSO algorithm, respectively. The results show that the calculated horizontal displacements and GPS observations are basically the same as when the points are far away from the fault, the RANSAC-PSO algorithm performs better than PSO when the calculating points are near the fault. The calculated value of LS07 completely coincides with GPS observations.
