郝锦绮. 1985: 唐山地震与震磁效应的最佳观测. 地震学报, 7(3): 300-313.
引用本文: 郝锦绮. 1985: 唐山地震与震磁效应的最佳观测. 地震学报, 7(3): 300-313.
1985: TANGSHAN 1976 EARTHQUAKE AND THE OPTIMUM OBSERVATION STRATEGY FOR SEISMOMAGNETISM. Acta Seismologica Sinica, 7(3): 300-313.
Citation: 1985: TANGSHAN 1976 EARTHQUAKE AND THE OPTIMUM OBSERVATION STRATEGY FOR SEISMOMAGNETISM. Acta Seismologica Sinica, 7(3): 300-313.

唐山地震与震磁效应的最佳观测

TANGSHAN 1976 EARTHQUAKE AND THE OPTIMUM OBSERVATION STRATEGY FOR SEISMOMAGNETISM

  • 摘要: 根据作者与Hastie和Stacey提出的三维压磁效应模式计算方法,围绕1976年唐山大地震,计算了七种不同断层模式的压磁效应,比较了在不同磁纬处,走向滑动断层的不同走向、倾角和埋深在地面上所引起的压磁异常场。结果表明,震磁效应的可观测性同地震的破裂机制有着紧密的关系。断层倾角45——60对应着最佳观测条件,其压磁异常峰值可高达12nT;在最差观测条件时压磁异常量几乎无法测出,这时断层位于磁纬0处,或走向为E-W,或埋深为10公里左右。在大多数模式中,垂直分量的异常略大于总强度异常,但在磁赤道附近可高达三倍左右。对唐山大地震的计算表明,压磁异常量约3——4nT,其异常大于1nT区域的线性尺度与断层长度之比仅为1.04——1.10。由于压磁场是地震过程的一种弱效应场,目前使用仪器的观测精度不够和磁测点的震中距过大,可能是未测出该地震明显的磁异常的原因。

     

    Abstract: Based on the theory of three-dimensional seismomagnetic modelling proposed by the author,Hastie and Staeey,a computation for the Tangshan 1976 earthquake is undertaken. The piezomagnetic anomalies of seven models with different orientations,dip angles and depths of the fault at different magnetic latitudes are compared. The results indicate that seismomagnetic effect is strongly dependent on the focal mechanism of the earthquake. It appears that strike-slip fault with a dip angle of 45-60 provides the optimum observation condition where the maximum piezomagnetic anomaly is as high as 12 nT. The worst condition for seismomagnetic observation appears when the fault is located at the magnetic equator,or orients magnetic E-W,or with a focal depth of 10 km o>r more. Under one of such circumstances the corresponding piezomagnetic anomaly can hardly be detected. In most of the models,anomaly of the vertical component is slightly higher than that of the total field strength and reaches an extreme value of three fold of the latter when the fault is located at the magnetic equator. Computation for the Tangshan earthquake shows that the maximum anomaly is about 3-4 nT and the ratio of the linear extension of the area with an anomaly exceeding InT to the fault length is only 1.04-1.10. Since the piezomagnetic field is a weakly induced field by an earthquake,the fact that no obvious magnetic precursor to this earthquake had been measured seems to 'be due to the low sensitivity of the magnetometers involved and their large epicentral distances.

     

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