Abstract: The source parameters characterize the main physical processes of an earthquake, while the velocity model is an approximate parameter representation of the real underground structure. Both are coupled in various ways, affecting the recording of seismic phases. In the past, when fitting the waveforms of a large number of regional earthquakes to invert for source parameters, low-computational-consumption one-dimensional velocity models were often used to model the seismic waveforms, and there was a lack of systematic and quantitative assessment of the absolute error in the source mechanism solution caused by the velocity model. This study takes the Longmenshan fault zone as an example, using a high-resolution three-dimensional velocity model obtained by wave imaging to accurately perform three-component broadband waveform synthesis for 212 representative regional earthquakes (M_S 3.5~5.7) after the Wenchuan earthquake, and based on this, multiple representative regional one-dimensional velocity models are used for source parameter CAP waveform inversion tests. By statistically analyzing the source parameters obtained from the waveform inversion of different one-dimensional models and comparing them with the representative seismic source parameters, the study systematically evaluates the impact of the accuracy of one-dimensional velocity models on the precision of the source parameter waveform inversion results. In this paper, under the filtered parameters for P-waves (0.01~0.18 Hz) and S-waves (0.03~0.10 Hz), the four sets of one-dimensional velocity model inversion mechanism solutions obtained are all quite reliable, with the number of events with an error Kagan angle less than 30° accounting for more than 97%. However, the CAP inversion depth error depends on the velocity model, and it is found that the inaccurate shallow structure will severely affect the inversion depth of the event. In the case of unknown accuracy of the velocity model, the normalized cross-correlation coefficient NCC of the seismic event can be used as a key indicator for the accurate inversion of the source depth. The velocity model accuracy assessment method and ideas proposed in this paper can be extended to the source inversion research of other complex tectonic areas and different one-dimensional velocity models.

Key words: Source parameter inversion, One-dimensional velocity model, Waveform fitting, Model evaluation