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-  2015 

Causative Structure of the 2013 Laizhou Earthquake Sequence

DOI: 10.3969/j.issn.1000-0844.2015.02.0546

Keywords: 莱州序列,发震构造,双差定位,CAP方法
Laizhou earthquake sequence
,causative structure,double-difference location,CAP method

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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 ML2.0.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 MW =


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