Missing earthquakes detection and seismogenic structure of the Yuxian earthquake swarm in August of 2013

The increasing seismicity of small earthquake swarms have been observed in North China area during recent years. Due to the lack of digital waveform recordings of large earthquakes in this area, detailed seismogenic structure analysis of earthquake swarms is of significance to seismic risk analysis and earthquake tendency judgement. We herein used matched filter technique to detect missing earthquakes in Yuxian small earthquake swarm occurred during August 22nd to 25th, 2013. By the technique we detected 18 missing earthquakes, which are about 1.38 times of 13 listed in the catalog. The seismogenic structure of the earthquake swarm can be divided into two parts. One is an NE-trending fault and more active in the early time of this earthquake swarm; the other is an NW-trending fault on which more earthquakes occurred in the later time. The seismicity is much stronger in the NW-trending fault than that in the NE-trending fault. According to focal mechanism of two lager earthquakes in the swarm, it is suggested that the mechanism of earthquakes occurred on the NW-trending fault are dominated by normal slip.