2013年山东莱州M4.6地震序列发震构造初探

采用双差定位法对山东莱州地震序列重新定位,通过CAP方法反演M4.6地震震源机制,在此基础上初步探讨莱州地震序列发震构造。结果显示:精确定位震中位置主要位于柞村—仙夼断裂的NW方向,深度剖面显示从SE方向到NW方向断层深度呈由浅逐渐变深的趋势,这均与柞村—仙夼断裂位置、走向、倾向特征较为吻合;M4.6地震震源机制解的节面Ⅰ与柞村—仙夼断裂走向、倾角较为接近。综合精确定位震中位置、剖面深度分布特征、M4.6地震震源机制解及宏观调查烈度分布等结果与柞村-仙夼断裂产状之间的关系,初步推测柞村—仙夼断裂可能为莱州地震序列的发震断层。

Causative Structure of the 2013 Laizhou Earthquake Sequence

The M4.6 earthquake in Laizhou,Shandong,occurred on November 23,2013,and it was the largest earthquake recorded since 1970.This event was also notable as the most potent earthquake in the interior regions since the M5.2 earthquake of Cangshan 18 years earlier.The Shandong Digital Earthquake Network Center has recorded 86 aftershocks until March 02,2014,including 18 earthquakes of more than M_L2.0.The earthquake occurred between the Jingzhi and Yishu faults (along NE direction) with the Liucun-Laizhou,Zuocun-Xiankuan,Matou-Dagu faults around the epicenter.The focal mechanism describes the nature and source of the rupture process,and is an important foundation for understanding the stress state of the source region,earthquake faults,and analyzing the causes of the seismic event.Therefore,the determination of the earthquake focal mechanisms is of great significance in the understanding of the mechanical process of earthquakes,for seismic interpretation,and for the understanding of the post-earthquake seismogenic stress distribution mechanism.Thus the causative structure of the Laizhou earthquake sequence is discussed on the basis of relocating the Laizhou earthquake sequence using the double-difference method and analyzing the focal mechanism of the stronger earthquake using the "cut and paste"(CAP) method.Eighty-six earthquakes were relocated using the double-difference method,and 75 basic earthquake parameters were obtained. The precise epicenter was located along the direction of Zuocun-Xiankuan fault,which is consistent with the location,strike,and dip of the Zuocun-Xiankuan fault.The depth of the entire earthquake sequence was found from 4 to 9 km,and the advantages of depth was at 5~7 km.The result showed that the main earthquake rupture occurred in the upper crust.The analysis of the vertical profile by precise positioning showed that the focal depth from SE to NW gradually becomes deeper,and the dip direction is in the NW direction,which are consistent with location,strike,and dip of the Zuocun-Xiankuang fault.The focal mechanism of the 4.6 earthquake was inverted using the CAP method.Thus,the synthetic seismograms fit well with the observed seismograms,and the inversion result is verified.The focal mechanism showed that the moment magnitude of the M4.6 earthquake was M_W = 4.5,one nodal plane had a strike of 193°,a rake of 144°,and a dip of 69°,and another nodal plane had a strike of 298°,a rake of 25°,and a dip of 57°.The first nodal plane appeared to have occurred close to the Zuocun-Xiankuang fault.Combining the precise relocation results,profile depth distribution,focal mechanism of the M4.6 earthquake,and intensity distribution by macroscopic investigation using the relationship of Zuocun-Xiankuang fault occurrence,it was concluded that the Zuocun-Xiankuang fault may be the seismogenic fault of Laizhou earthquake sequence.