宁洱地震序列的震源机制解分析
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摘要
利用云南数字地震台网资料得到宁洱地震序列的主震、5.1级强余震和52个余震震源机制解。分析表明,该地震序列的发震断裂呈NW走向,倾角陡立。在接近水平的近南北向压应力作用下,断裂具有右旋走滑的错动性质。主震、强余震和众多的余震都发生在同一发震断裂上。大量的余震震源机制解结果与主震一致,是地震序列的主要破裂类型,但还存在与主要类型不一致的倾向滑动类型,这可能与余震破裂起始点的微构造控制作用有关,但是它们呈水平向的应力轴与主震的主应力轴一致。NW向断层作右旋走向错动,滑动断层推挤的象限都是逆冲类型的余震,而拉张的象限都是正断层类型的地震。宁洱地震序列的震源机制和周围4次5级以上地震的震源机制相同,表明震源区应力场和区域应力场完全一致,宁洱地震的孕育和发生受区域应力场的控制。
Using the data recorded by the Yunnan Digital Seismic Network,we calculate the focal mechanisms of the Ning'er MS6.2 main shock,the MS5.1 strong aftershock and other 51 aftershocks.The results show that the seismogenic fault was NW-ward and the dip angle was nearly vertical.The fault was right-lateral,strike-slip,which was effected by the nearly horizontal,principal,NS-ward compressive stress.The main shock,strong aftershock and some aftershocks occurred on the same seismogenic fault.The focal mechanism of many aftershocks were consistent with the main shock's,which were the main types of the earthquake sequence.The dip-slip aftershocks inconsistent with the main shock showed the adjustment process of the stress field of the focal region,whereas the nearly horizontal press axes were consistent with the main shock.Because of the right-lateral,strike-slip of the NW-ward fault,the reverse aftershocks occurred in the pressing quadrant while the normal quakes occurred in tensional quadrant.The focal mechanism was consistent with those of other four earthquakes with MS≥5.0 around the Ning'er earthquake stricken area,which showed the consistency in the focal region stress field and regional stress field,and the genesis and occurrence of the Ning'er earthquake were controlled by the regional stress field.
Using the data recorded by the Yunnan Digital Seismic Network,we calculate the focal mechanisms of the Ning'er MS6.2 main shock,the MS5.1 strong aftershock and other 51 aftershocks.The results show that the seismogenic fault was NW-ward and the dip angle was nearly vertical.The fault was right-lateral,strike-slip,which was effected by the nearly horizontal,principal,NS-ward compressive stress.The main shock,strong aftershock and some aftershocks occurred on the same seismogenic fault.The focal mechanism of many aftershocks were consistent with the main shock's,which were the main types of the earthquake sequence.The dip-slip aftershocks inconsistent with the main shock showed the adjustment process of the stress field of the focal region,whereas the nearly horizontal press axes were consistent with the main shock.Because of the right-lateral,strike-slip of the NW-ward fault,the reverse aftershocks occurred in the pressing quadrant while the normal quakes occurred in tensional quadrant.The focal mechanism was consistent with those of other four earthquakes with MS≥5.0 around the Ning'er earthquake stricken area,which showed the consistency in the focal region stress field and regional stress field,and the genesis and occurrence of the Ning'er earthquake were controlled by the regional stress field.
引文
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许忠淮.1979.京津唐张地区地震应力场的方向特征[J].地震学报,1(2):52-58.
K is slinger C,Bowman J R,Koch K.1981.Procedures for computing fo-cal mechanisms from local(SV/P)Z data[J],BSSA,71(6):1719-1729.
S no ke J A.1989.Earthquake mechanism[C]//James D E.Encyclope-dia of Geophysics.New York:Van Nostrand Reinhold Company,239-245.
付虹,王绍晋,龙晓帆,等.2009.利用数字化速度波形和仿真位移波形资料求解震源机制解的比较[J].32(1):18-24.
虢顺民,汪洋,计凤桔.1999.云南思茅—普洱地区中强震群发生的构造机制[J].地震研究,22(2):105-115.
华祥文.1980.唐山强震前后北京、天津周围地区应力场的变化过程[J].地震学报,2(2):62-72.
阚荣举,张四昌,晏凤桐,等.1977.我国西南地区现代构造应力场与现代构造活动特征的探讨[J].地球物理学报,20(2):96-109.
梁尚鸿,李幼铭,束沛镒,等.1984.利用区域地震台网P、S振幅比资料测定小震震源参数[J].地球物理学报,27(3):249-257.
王绍晋,阚荣举,胡克坚,等.1989.云贵地区现代构造应力场空间分布与地震危险区划[C]//云贵地区地震危险性研究文集.昆明:云南科技出版社.
谢富仁,苏刚,崔效锋,等.2001.滇西南地区现代构造应力场分析[J].地震学报,23(1):17-23.
许忠淮.1979.京津唐张地区地震应力场的方向特征[J].地震学报,1(2):52-58.
K is slinger C,Bowman J R,Koch K.1981.Procedures for computing fo-cal mechanisms from local(SV/P)Z data[J],BSSA,71(6):1719-1729.
S no ke J A.1989.Earthquake mechanism[C]//James D E.Encyclope-dia of Geophysics.New York:Van Nostrand Reinhold Company,239-245.
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