Determining the fault planes in the North China Plain with a combination of the earthquake location data and the focal mechanism solutions

The active faults on the North China Plain (or NC Plain), a crucial region of China containing the center of Chinese politics, industry, and economy, has long been the focus of todays seismology research. Based on the fault plane fitting algorithm developed by Wan et al. (2008), which has been applied in estimating the fault geometrics from Tangshan earthquake clusters, we introduced a new fault parameter determining algorithm which combines the small earthquake location data and focal mechanism solutions, and investigated the recent active faults in the NC Plain. 7 fault planes containing their strikes, dips, rakes, and locations have been determined with their solution accuracy analyzed. Forming an NE extending fault chain, 4 NE faults show right-lateral strike slip features, while 2 NW faults near the NC Plain boundary slip left-laterally, a finding consists with Zhang et al.s (2018) GPS research on the NC Plain deformation. Furthermore, 5 out of the 7 fault solutions are coincident with the surface fault data, while the rest 2 near the center of the NC Plain can be explained with 2 buried active faults. Though the reason for their formation and the silence of their nearby faults remains unclear, the existence of these buried faults contribute to the emergence of a seismic active fault chain extending from the southwest of the NC Plain to its northeast, whose seismicity features and the role in the future release of the stress in the NC crust need follow-up studies. The result can be further used in seismic hazard estimation. This work is supported by the National key research and development program (Grant No. 2018YFC1504203) References: Wan, Y. G., Shen, Z. K., Diao, G. L., Wang, F. C., Hu, X. L., Sheng, S. Z. (2008). An. algorithm of fault parameter determination using distribution of small earthquakes and parameters of regional stress field and its application to Tangshan earthquake sequence. Chinese J. Geophysics. (in Chinese), 2008, 51 (3): 793~804. Zhang, Y. G., Zheng, W. J., Wang, Y. J., Zhang, D. L., Tian, Y. T., Wang, M., et al. (2018). Contemporary deformation of the North China plain from global positioning system data. Geophysical Research Letters, 45, 1851 1859.