There have been many intensive small earthquakes since the M 3.8 earthquake occurred in Rushan,Shandong on October 1,2013.Two earthquakes(M 4.2 and M 4.0)occurred separately on January 7 and April 4,2014.There have never been so many earthquakes in Rushan.A focal mechanism describes the nature and source rupture process and is an important foundation to un-derstand the stress state of the source region,earthquake faults,and for analyzing the causes of a seismic event.Therefore,seismic interpretation and post-earthquake seismogenic stress distribu-tion mechanisms play very important roles in determining earthquake focal mechanisms.In this study,using waveforms from the Shandong Seismological Network and comparing the synthetic and the observed seismograms,the focal mechanism of the Rushan M 4.2 and M 4.0 earthquakes in 2014 are inverted using the CAP(Cut and paste)method.The results show that the two earth-quakes get their best focal mechanism at 6 km depth,and that the parameters of the nodal planes are similar,belonging to the strike-slip type.At a depth of 6 km,the correlation coefficients of 40 phases of the M 4.2 earthquake greater than 0.7 that were recorded by eight stations are 37,which accounts for 93%.The correlation coefficients greater than 0.9 are 28,accounting for about 70%. Similarly,at a depth of 6 km,the correlation coefficients of 40 phases of the M 4.0 earthquake that were recorded by the eight stations are all greater than 0.7 and the correlation coefficients greater than 0.9 are 31,accounting for about 78%.Therefore,the synthetic seismograms of the two earth-quakes fit the observed seismograms well demonstrating that the inversion results are credible. The focal mechanism shows that the moment magnitude of the M 4.2 earthquake was M W =4.3;one nodal plane has a strike of 290°,rake of 84°,and dip of 22°and the other nodal plane has a strike of 189°,rake of 68°,and dip of 174°.The moment magnitude of the M 4.0 earthquake is M W=4.2,one nodal plane has a strike of 289°,rake of 90°,and dip of 27°and the other nodal plane has a strike of 1 99°,rake of 63°,and a dip of 180°,The hypocentral distance was calculated by the mo-bile seismic station near the epicenter.The results show that the focal depth is slightly less than 7 km,which is consistent with the inversion results of the CAP method,and therefore,the main rupture of the earthquake was in the upper crust.The parameters of the Rushan fault nearest to the epicenter (strike of 10°normal fault)are not consistent with the focal mechanisms of the two earthquakes,which show that the Rushan fault is not the seismic fault and that the seismic faults may be concealed faults.%选用山东数字地震台网波形资料,利用 CAP 方法反演乳山2014年1月7日 M 4.2及4月4日 M 4.0地震震源机制解。反演结果显示,两次地震均在矩心深度为6 km 处获得最佳震源机制解,其节面参数基本一致,属于近走滑型地震。震中附近流动台站的震源距计算表明地震序列震源深度应略小于7 km,与 CAP 方法反演结果具有一致性,表明地震的主体破裂发生在上地壳。
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