Abstract: Currently, the methods used in the study of the focal mechanism of small and moderate earthquakes in the capital region include the P-wave first motion polarity method, the amplitude ratio method and the waveform inversion method. The former two methods use only a small amount of information in the waveforms, and are limited by factors such as the station distribution, site effects etc. Similarly, the traditional waveform inversion method only uses part of the information of the waveform, and there are certain requirements for the magnitude and data quality, etc. To overcome the aforementioned limitations, this study attempts to use a new full waveform matching method, which uses comprehensive information mentioned above, to invert for the focal mechanism solution of earthquakes of small and moderate magnitude in the Capital Region, thereby improving the reliability of the solution. To test the reliability and applicability of the new full waveform matching method for the earthquakes in the capital region, we first perform a synthetic data test. The test results prove that the used full waveform matching method is stable and reliable. In early 2019, two recent M3+ earthquakes occurring in Beijing received extensive attention. We use the full waveform matching method to determine their focal mechanism solutions and analyze their occurrence in the background of regional active faults. Finally, we determine the focal mechanisms for 22 earthquakes (2.2≤M≤4.3) since 2015 in the capital region, and analyze the tectonic stress field in the capital region, which compares well with previous studies.

Key words: The capital region, Focal mechanism, Full waveform matching, Neighborhood algorithm