Research On Reverse Time Migration Imaging Method Based On The High-speed Train Seismic Source

In China,high-speed railways have developed rapidly and have come to world prominence.The railway network is ramified and criss-cross all over the country.And the high-speed trains repeatedly run for a long time at almost uniform speed,constituting a new stable and repeatable artificial seismic source,namely the high-speed train seismic source,and generating massive seismic data.Research shows that the seismic data excited by the high-speed trains contains abundant train running status information and geological environmental information,which is of great significance for the safety monitoring of the high-speed railway environment.In this paper,we mainly focus on the reverse time migration method based on the high-speed train seismic source,which mainly includes the following parts:(1)Taking the CRH5 high-speed train as an example,construct a load model of the high-speed train.The excitation mechanism of seismic waves when the high-speed train passes by is simplified as the linear superposition of a series of wheel axles on the front and rear bogies of the carriages on the track and the medium.And then the high-speed train seismic source time function is constructed,and the time history of seismic source excited by a moving high-speed train is given.(2)In order to better model the seismic waves excited by high-speed trains and avoid the disturbance of numerical errors,an improved particle swarm optimization(PSO)algorithm,which introduces the local learning strategy and the global learning strategy,is proposed and used to obtain an optimized finite-difference(FD)operator.The optimized FD operator based on the improved PSO algorithm has wider spectrum coverage,while ensuring the accuracy error.Then the optimized FD operator is used for performing numerical modelling.And numerical modelling results indicate that the optimized FD operator based on the improved PSO algorithm can effectively reduce numerical errors.(3)According to the high-speed train seismic source time function and the optimized FD numerical modelling strategy based on the improved PSO algorithm,the numerical modelling of seismic waves excited by the moving high-speed trains is realized.And the characteristics of the seismic wave field generated by the moving high-speed trains are analyzed.(4)According to the high-speed train seismic source time function,high-precision numerical modelling scheme of seismic waves excited by the moving high-speed trains,and cross-correlation imaging conditions,reverse time migration imaging method based on the high-speed train seismic source is realized.The results of migration imaging indicate that,the abundant geological environmental information can be effectively extracted from the seismic data excited by the moving high-speed trains.