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Author(s):: QIN Jia-zheng¹; QIAN Xiao-dong¹; ZHAO Xiao-yan¹; LIU Li-fang¹; (Earthquake Administration of Yunnan Province,Kunming 650224,Yunnan,China)

Keywords:: shear stress value τ₀; focal mechanism; image of stress; East Asia seismic zone

摘要:: 为对云南强震活动趋势分析提供科学依据,基于Haskell二维地震位错模型,建立了用地震矩M₀和体波震级m_b估算地震震源构造剪应力强度τ₀值的关系,并利用此关系,根据美国地质调查局提供的1977～2005年间东亚滇缅弧—安达曼地震活动带上强震活动的震源机制解、地震矩M₀和体波震级m_b,对该区的地震应力图像和板缘动力学机制特征进行了深入分析。结果表明:缅甸弧—安达曼板缘地震带的强震活动主要反映了板缘地震活动的特点,其平均剪应力τ₀值为8.8 MPa; 云南及喜马拉雅山地区的少量强震活动主要反映了板内地震活动的特征,其平均剪应力τ₀值为13.5 MPa,板内地震统计得出的平均剪应力值是板缘地震的1.5倍。喜马拉雅山弧形区域主压应力方向(P轴)优势方向为NE向,但青藏高原东南的云南地区则表现出向ES方向的强烈偏转,这可能是由于印度板块与欧亚板块的强烈碰撞挤压以及缅甸弧的弧后扩张相互作用引起的。

Abstract:: In order to provide scientific basis for the seismicity tendency analysis of the Yunnan region,we build the relation to estimate shear stress value τ₀ with seismic moment M₀ and body wave magnitude m_b based on the Haskell two-dimensional seismic dislocations model.We use the relation to estimate the τ₀ value in the Yunnan-Burma arc and Andaman seismic zone according to the 1977-2005 data from USGS in the area,and analyze the image of stress and the characteristics of intraplate dynamic mechanism in the area.The analytical results indicate that the earthquakes in Burma arc and Andaman seismic zone mainly characterize interplate seismicity,and the average τ₀ value is 8.8 Mpa; the earthquakes in the other areas mainly characterize intraplate seismicity,and the average τ₀ value is 13.5 Mpa,about 1.5 times as much as that of interplate earthquakes.In the Himalaya mountains arc area,the compressive stress is in NE direction,while in the Yunnan region southeast of Qinghai-Tibet Plateau,the compressive stress shows a remarkable rotation toward SE direction,which may be caused by the joint effect of the continental collision and extrusion between the India and Eurasia plates and the back-arc extension in the Burma arc region.